General Approach to the Vascular Patient

June 4, 2024
0
0
Зміст

TOPIC №8. Obliterating diseases of arteries. Abdominal angina

General Approach to the Vascular Patient

Because the vascular system involves every organ system in our body, the symptoms of vascular disease are as varied as those encountered in any medical specialty. Lack of adequate blood supply to target organs typically presents with pain; for example, calf pain with lower extremity (LE) claudication, postprandial abdominal pain from mesenteric ischemia, and arm pain with axillosubclavian arterial occlusion. In contrast, stroke and transient ischemic attack (TIA) are the presenting symptoms from middle cerebral embolization as a consequence of a stenosed internal carotid artery (ICA). The pain syndrome of arterial disease usually is divided clinically into acute and chronic types, with all shades of severity between the two extremes. Sudden onset of pain can indicate complete occlusion of a critical vessel, leading to more severe pain and critical ischemia in the target organ, resulting in lower limb gangrene or intestinal infarction. Chronic pain results from a slower, more progressive atherosclerotic occlusion, which can be totally or partially compensated by developing collateral vessels. Acute on chronic is another pain pattern in which a patient most likely has an underlying arterial stenosis that suddenly occludes; for example, the patient with a history of calf claudication who now presents with sudden, severe acute limb-threatening ischemia. The clinician should always try to understand and relate the clinical manifestations to the underlying pathologic process.

Vascular History

Appropriate history should be focused on the presenting symptoms related to the vascular system (Table 1). Of particular importance in the previous medical history is noting prior vascular interventions (endovascular or open surgical), and all vascular patients should have inquiry made about their prior cardiac history and current cardiac symptoms. Approximately 30% of vascular patients will be diabetic. A history of prior and current smoking status should be noted.

 

Table 1. Pertinent Elements in Vascular History

 

The patient with carotid disease in most cases is completely asymptomatic, having been referred based on the finding of a cervical bruit or duplex finding of stenosis. Symptoms of carotid territory TIAs include transient monocular blindness (amaurosis), contralateral weakness or numbness, and dysphasia. Symptoms persisting longer than 24 hours constitute a stroke. In contrast, the patient with chronic mesenteric ischemia is likely to present with postprandial abdominal pain and weight loss. The patient fears eating because of the pain, avoids food, and loses weight. It is very unlikely that a patient with abdominal pain who has not lost weight has chronic mesenteric ischemia.

The patient with LE pain on ambulation has intermittent claudication that occurs in certain muscle groups; for example, calf pain upon exercise usually reflects superficial femoral artery (SFA) disease, while pain in the buttocks reflects iliac disease. In most cases, the pain manifests in one muscle group below the level of the affected artery, occurs only with exercise, and is relieved with rest only to recur at the same location, hence the term window gazers disease. Rest pain (a manifestation of severe underlying occlusive disease) is constant and occurs in the foot (not the muscle groups), typically at the metatarsophalangeal junction, and is relieved by dependency. Often, the patient is prompted to sleep with their foot hanging off one side of the bed to increase the hydrostatic pressure.

Vascular Physical Examination

Specific vascular examination should include abdominal aortic palpation, carotid artery examination, and pulse examination of the LE (femoral, popliteal, posterior tibial, and dorsalis pedis arteries). The abdomen should be palpated for an abdominal aortic aneurysm (AAA), detected as an expansile pulse above the level of the umbilicus. It also should be examined for the presence of bruits. Because the aorta typically divides at the level of the umbilicus, an aortic aneurysm is most frequently palpable in the epigastrium. In thin individuals, a normal aortic pulsation is palpable, while in obese patients even large aortic aneurysms may not be detectable. Suspicion of a clinically enlarged aorta should lead to the performance of an ultrasound scan for a more accurate definition of aortic diameter.

The carotids should be auscultated for the presence of bruits, although there is a higher correlation with coronary artery disease (CAD) than underlying carotid stenosis. A bruit at the angle of the mandible is a significant finding, leading to follow-up duplex scanning. The differential diagnosis is a transmitted murmur from a sclerotic or stenotic aortic valve. The carotid is palpable deep to the sternocleidomastoid muscle in the neck. Palpation, however, should be gentle and rarely yields clinically useful information.

Upper extremity examination is necessary when an arteriovenous graft is to be inserted in patients who have symptoms of arm pain with exercise. Thoracic outlet syndrome can result in occlusion or aneurysm formation of the subclavian artery. Distal embolization is a manifestation of thoracic outlet syndrome; consequently, the fingers should be examined for signs of ischemia and ulceration. The axillary artery enters the limb below the middle of the clavicle, where it can be palpated in thin patients. It usually is easily palpable in the axilla and medial upper arm. The brachial artery is most easily located at the antecubital fossa immediately medial to the biceps tendon. The radial artery is palpable at the wrist anterior to the radius.

For LE vascular examination, the femoral pulse usually is palpable midway between the anterior superior iliac spine and the pubic tubercle. The popliteal artery is palpated in the popliteal fossa with the knee flexed to 45° and the foot supported on the examination table to relax the calf muscles. Palpation of the popliteal artery is a bimanual technique. Both thumbs are placed on the tibial tuberosity anteriorly and the fingers are placed into the popliteal fossa between the two heads of the gastrocnemius muscle. The popliteal artery is palpated by compressing it against the posterior aspect of the tibia just below the knee. The posterior tibial pulse is detected by palpation 2 cm posterior to the medial malleolus. The dorsalis pedis is detected 1 cm lateral to the hallucis longus extensor tendon, which dorsiflexes the great toe and is clearly visible on the dorsum of the foot. Pulses can be graded using either the traditional four-point scale or the basic two-point scale system (Table 2). The foot also should be carefully examined for pallor on elevation and rubor on dependency, as these findings are indicative of chronic ischemia. Note should also be made of nail changes and loss of hair. Ulceration and other findings specific to disease states are described in relevant sections below.

Table 2 Grading Scales for Peripheral Pulses

After reconstructive vascular surgery, the graft may be available for examination, depending on its type and course. The in situ LE graft runs in the subcutaneous fat and can be palpated along most of its length. A change in pulse quality, aneurysmal enlargement, or a new bruit should be carefully noted. Axillofemoral grafts, femoral-to-femoral grafts, and arteriovenous access grafts usually can be easily palpated as well.

 

Noninvasive Diagnostic Evaluation of the Vascular Patient

Ankle-Brachial Index

There is increasing interest in the use of the ankle-brachial index (ABI) to evaluate patients at risk for cardiovascular events. An ABI <0.9 correlates with increased risk of myocardial infarction and indicates significant, although perhaps asymptomatic, underlying peripheral vascular disease. The ABI is determined in the following ways. Blood pressure (BP) is measured in both upper extremities using the highest systolic BP as the denominator for the ABI. The ankle pressure is determined by placing a BP cuff above the ankle and measuring the return to flow of the posterior tibial and dorsalis pedis arteries using a pencil Doppler probe over each artery. The ratio of the systolic pressure in each vessel divided by the highest arm systolic pressure can be used to express the ABI in both the posterior tibial and dorsalis pedis arteries (Fig. 1). Normal is more than 1. Patients with claudication typically have an ABI in the 0.5 to 0.7 range, and those with rest pain are in the 0.3 to 0.5 range. Those with gangrene have an ABI of <0.3. These ranges can vary depending on the degree of compressibility of the vessel. The test is less reliable in patients with heavily calcified vessels. Due to noncompressibility, some patients such as diabetics and those with end-stage renal disease may have an ABI of 1.40 or greater and require additional noninvasive diagnostic testing to evaluate for peripheral arterial disease (PAD). Alternative tests include toe-brachial pressures, pulse volume recordings, transcutaneous oxygen measurements, or vascular imaging (duplex ultrasound).

Fig. 1. Ankle-Brachial Index

Segmental Limb Pressures

By placing serial BP cuffs down the LE and then measuring the pressure with a Doppler probe as flow returns to the artery below the cuff, it is possible to determine segmental pressures down the leg. These data can then be used to infer the level of the occlusion. The systolic pressure at each level is expressed as a ratio, with the highest systolic pressure in the upper extremities as the denominator. Normal segmental pressures commonly show high thigh pressures 20 mmHg or greater in comparison to the brachial artery pressures. The low thigh pressure should be equivalent to brachial pressures. Subsequent pressures should fall by no more than 10 mmHg at each level. A pressure gradient of 20 mmHg between two subsequent levels is usually indicative of occlusive disease at that level. The most frequently used index is the ratio of the ankle pressure to the brachial pressure, the ABI. Normally the ABI is >1.0, and a value <0.9 indicates some degree of arterial obstruction and has been shown to be correlated with an increased risk of coronary heart disease.1 Limitations of relying on segmental limb pressures include: (a) missing isolated moderate stenoses (usually iliac) that produce little or no pressure gradient at rest; (b) falsely elevated pressures in patients with diabetes and end-stage renal disease; and (c) the inability to differentiate between stenosis and occlusion.2 Patients with diabetes and end-stage renal disease have calcified vessels that are difficult to compress, thus rendering this method inaccurate, due to recording of falsely elevated pressure readings. Noncompressible arteries yield ankle systolic pressures of 250 mmHg or greater and an ABI of >1.40. In this situation, absolute toe and ankle pressures can be measured to gauge critical limb ischemia. Ankle pressures <50 mmHg or toe pressures <30 mmHg are indicative of critical limb ischemia. The toe pressure is normally 30 mmHg less than the ankle pressure, and a toe-brachial index of <0.70 is abnormal. False-positive results with the toe-brachial index are unusual. The main limitation of this technique is that it may be impossible to measure pressures in the first and second toes due to pre-existing ulceration.

Pulse Volume Recording

In patients with noncompressible vessels, segmental plethysmography can be used to determine underlying arterial occlusive disease. Cuffs placed at different levels on the leg detect changes in leg volume and produce a pulse volume recording (PVR) when connected to a plethysmograph (Fig. 2). To obtain accurate PVR waveforms the cuff is inflated to 60 to 65 mmHg to detect volume changes without causing arterial occlusion. Pulse volume tracings are suggestive of proximal disease if the upstroke of the pulse is not brisk, the peak of the wave tracing is rounded, and there is disappearance of the dicrotic notch.

Fig. 2 A Pulse volume recording is done by connecting blood pressure cuffs and plethysmograph to various levels of the leg

Fig. 2 B Typical report of peripheral vascular study with arterial segmental pressure measurement plus Doppler evaluation of the lower extremity.

Although isolated segmental limb pressures and PVR measurements are 85% accurate when compared with angiography in detecting and localizing significant atherosclerotic lesions, when used in combination, accuracy approaches 95%.3 For this reason, it is suggested that these two diagnostic modalities be used in combination when evaluating PAD.

 

Radiological Evaluation of the Vascular Patient

 

Ultrasound

Ultrasound examinations are relatively time consuming, require experienced technicians, and may not visualize all arterial segments. Doppler waveform analysis can suggest atherosclerotic occlusive disease if the waveforms in the insonated arteries are biphasic, monophasic, or asymmetrical. B-mode ultrasonography provides black and white, real-time images. B-mode ultrasonography does not evaluate blood flow; thus, it cannot differentiate between fresh thrombus and flowing blood, which have the same echogenicity. Calcification in atherosclerotic plaques will cause acoustic shadowing. B-mode ultrasound probes cannot be sterilized. Use of the B-mode probe intraoperatively requires a sterile covering and gel to maintain an acoustic interface. Experience is needed to obtain and interpret images accurately. Duplex ultrasonography entails performance of B-mode imaging, spectral Doppler scanning, and color flow duplex scanning. The caveat to performance of duplex ultrasonography is meticulous technique by a certified vascular ultrasound technician, so that the appropriate 60° Doppler angle is maintained during insonation with the ultrasound probe. Alteration of this angle can markedly alter waveform appearance and subsequent interpretation of velocity measurements. Direct imaging of intra-abdominal vessels with duplex ultrasound is less reliable because of the difficulty in visualizing the vessels through overlying bowel. These disadvantages currently limit the applicability of duplex scanning in the evaluation of aortoiliac and infrapopliteal disease. In a recent study, duplex ultrasonography had lower sensitivity in the calculation of infrapopliteal vessel stenosis in comparison to conventional digital subtraction or computer tomography angiography.4 Few surgeons rely solely on duplex ultrasonography for preoperative planning in LE revascularizations. However, in the hands of experienced ultrasonographers, LE arteries can be assessed accurately by determining the significance of velocity criteria across the arterial stenosis. Duplex scanning is unable to evaluate recently implanted polytetrafluoroethylene (PTFE) and polyester (Dacron) grafts because they contain air, which prevents ultrasound penetration.

Computed Tomography Angiography

Computed tomography angiography (CTA) is a noninvasive, contrast-dependent method for imaging the arterial system. It depends on IV infusion of iodine-based contrast agents. The patient is advanced through a rotating gantry, which images serial transverse slices. The contrast-filled vessels can be extracted from the slices and rendered in three-dimensional format (Fig. 3). The extracted images can also be rotated and viewed from several different directions during postacquisition image processing. This technology has been advanced as a consequence of aortic endografting. CTA provides images for postprocessing that can be used to display the aneurysm in a format that demonstrates thrombus, calcium, lumen, and the outer wall, and allows “fitting” of a proposed endograft into the aneurysm (Fig. 4). CTA is increasingly being used to image the carotid bifurcation, and as computing power increases, the speed of image acquisition and resolution will continue to increase. The major limitations of multidetector CTA are use of contrast and presence of artifacts caused by calcification and stents. CTA can overestimate the degree of instent stenosis, while heavy calcification can limit the diagnostic accuracy of the method by causing a ”blooming artifact.”5 The artifacts can be overcome with alteration in image acquisition technique. There are no randomized trials to document the superiority of multidetector CTA over traditional angiography, but there is emerging evidence to support the claim that multidetector CTA has sensitivity, specificity, and accuracy that rival invasive angiography.

Fig. 3 A. A multidetector computed tomographic angiogram with three-dimensional reconstruction of the iliofemoral arterial circulation in two patients with lower leg claudication. A 50-year-old man with an occluded right superficial femoral artery (single long arrow) with reconstituted superficial femoral artery at the level of midthigh. Arterial calcifications (short arrows) in the bilateral distal superficial femoral arteries.

Fig. 3 B. A multidetector computed tomographic angiogram with three-dimensional reconstruction of the iliofemoral arterial circulation in two patients with lower leg claudication.

 

Fig. 4. Three-dimensional computed tomographic angiogram of an abdominal aortic aneurysm that displays various aneurysm components, including thrombus, aortic calcification, blood circulation, and aneurysm wall.

Magnetic Resonance Angiography

Magnetic resonance angiography (MRA) has the advantage of not requiring iodinated contrast agents to provide vessel opacification (Fig. 5). Gadolinium is used as a contrast agent for MRA studies, and as it is generally not nephrotoxic, it can be used in patients with elevated creatinine. MRA is contraindicated in patients with pacemakers, defibrillators, spinal cord stimulators, intracerebral shunts, cochlear implants, and cranial clips. Patients with claustrophobia may require sedation to be able to complete the test. The presence of metallic stents causes artifacts and signal dropout; however, these can be dealt with using alternations in image acquisition and processing. Nitinol stents produce minimal artifact.6 Compared to other modalities, MRA is relatively slow and expensive. However, due to its noninvasive nature and decreased nephrotoxicity, MRA is being used more frequently for imaging vasculature in various anatomic distributions.

Fig. 5. Magnetic resonance angiogram of aortic arch and carotid arteries. This study can provide a three-dimensional analysis of vascular structures such as aortic arch branches, as well as carotid and vertebral arteries

 

Diagnostic Angiography

Diagnostic angiography is considered the gold standard in vascular imaging. In many centers, its use is rapidly decreasing due to the development of noninvasive imaging modalities such as duplex arterial mapping, CTA, and MRA. Nevertheless, contrast angiography still remains in widespread use. The essential aspects of angiography are vascular access and catheter placement in the vascular bed that requires examination. The imaging system and the contrast agent are used to opacify the target vessel. Although in the past this function has largely been delegated to the interventional radiology service, an increasing number of surgeons are performing this procedure and following the diagnostic imaging with immediate surgical or endovascular intervention. There are several considerations when relying on angiography for imaging.

Approximately 70% of atherosclerotic plaques occur in an eccentric location within the blood vessel; therefore, images can be misleading when trying to evaluate stenoses because angiography is limited to a uniplanar “lumenogram.” With increased use of intravascular stent deployment, it has been also noted that assessment of stent apposition and stent position in relation to surrounding branches may be inaccurate. Furthermore, angiography exposes the patient to the risks of both ionizing radiation and intravascular contrast. Nevertheless, contrast angiography remains the most common invasive method of vascular investigation for both diagnostic and therapeutic intervention. The angiogram usually provides the final informatioeeded to decide whether or not to proceed with operation or endovascular interventions.

Digital subtraction angiography (DSA) offers some advantages over conventional cut-film angiography, such as excellent visualization despite use of lower volumes of contrast media. In particular when multilevel occlusive lesions limit the amount of contrast reaching distal vessels, supplemental use of digital subtraction angiographic techniques may enhance visualization and definition of anatomy. Intra-arterial DSA uses a portable, axially rotatable imaging device that can obtain views from different angles. DSA also allows for real-time video replay (Fig. 6). An entire extremity can be filmed with DSA, using repeated injections of small amounts of contrast agent to obtain sequential angiographic images, the so-called pulse-chase technique.

Fig. 6. Digital subtraction angiography provides excellent visualization of intravascular circulation with intra-arterial contrast administration. As depicted in this digital subtraction angiography study, multilevel lesions are demonstrated that include a focal left iliac artery stenosis (large arrow), right superficial femoral occlusion (curved arrows), left superficial femoral stenosis (small arrow), and multiple tibial artery stenoses (arrowheads).

 

Preoperative Cardiac Evaluation

The most important and controversial aspect of preoperative evaluation in patients with atherosclerotic disease requiring surgical intervention is the detection and subsequent management of associated CAD. Several studies have documented the existence of significant CAD in 40 to 50% or more of patients requiring peripheral vascular reconstructive procedures, 10 to 20% of whom may be relatively asymptomatic largely because of their inability to exercise. Myocardial infarction is responsible for the majority of both early and late postoperative deaths. Most available screening methods lack sensitivity and specificity to predict postoperative cardiac complications. There have been conflicting reports regarding the utility of preoperative dipyridamole-thallium nuclear imaging or dobutamine-echocardiography to stratify vascular patients in terms of perioperative cardiac morbidity and mortality. Iearly one half of patients, thallium imaging proves to be unnecessary because cardiac risk can be predicted by clinical information alone. Even with coronary angiography, it is difficult to relate anatomic findings to functional significance, and hence, surgical risk. There are no data confirming that percutaneous coronary interventions or surgical revascularization before vascular surgical procedures impacts mortality or incidence of myocardial infarctions. In fact, coronary angiography is associated with its own inherent risks, and patients undergoing coronary artery bypass grafting or coronary percutaneous transluminal angioplasty (PTA) before needed aortoiliac reconstructions are subjected to the risks and complications of both procedures.

The Coronary Artery Revascularization Prophylaxis trial showed that coronary revascularization in patients with peripheral vascular disease and significant CAD, who are considered high risk for perioperative complications, did not reduce overall mortality or perioperative myocardial infarction. Additionally, patients who underwent prophylactic coronary revascularization had significant delays before undergoing their vascular procedure and increased limb morbidity compared to patients who did not. Studies do support improvement in cardiovascular and overall prognosis with medical optimization of patients. Therefore, use of perioperative beta blockade, as well as use of antiplatelet medication, statins, and angiotensin-converting enzyme (ACE) inhibitors is encouraged in vascular patients

 

AORTOILIAC OCCLUSIVE DISEASE

The distal abdominal aorta and the iliac arteries are common sites affected by atherosclerosis. The symptoms and natural history of the atherosclerotic process affecting the aortoiliac arterial segment are influenced by the disease distribution and extent. Atherosclerotic plaques may cause clinical symptoms by restricting blood flow due to luminal obstruction or by embolizing atherosclerotic debris to the LE circulation. If the aortoiliac plaques reach sufficient mass that impinge on the arterial lumen, obstruction of blood flow to lower extremities occurs. Various risk factors exist that can lead to the development of aortoiliac occlusive disease. Recognition of these factors and understanding this disease entity will enable physicians to prescribe the appropriate treatment strategy that may alleviate symptoms and improve quality of life.

Diagnostic Evaluation

On clinical examination, patients often have weakened femoral pulses and a reduced ABI. Verification of iliac occlusive disease is usually made by color duplex scanning that reveals either a peak systolic velocity ratio of 2.5 or greater at the site of stenosis and/or a monophasic waveform. Noninvasive tests such as pulse volume recording (PVR) of the LE with estimation of the thigh-brachial pressure index may be suggestive of aortoiliac disease. MRA and multidetector CTA are increasingly being used to determine the extent and type of obstruction. DSA offers the interventionalist the benefit of making a diagnosis and the option of performing an endovascular treatment in a single session. Angiography provides important information regarding distal arterial runoff vessels as well as the patency of the profunda femoris artery (PFA). Presence of pelvic and groin collaterals is important in providing crucial collateral flow in maintaining lower limb viability. It must be emphasized, however, that patients should be subjected to angiography only if their symptoms warrant surgical intervention.

Differential Diagnosis

Degenerative hip or spine disease, lumbar disc herniation, spinal stenosis, diabetic neuropathy, and other neuromuscular problems can produce symptoms that may be mistaken for vascular claudication. Such cases can be distinguished from true claudication by the fact that the discomfort from neuromuscular problems often is relieved by sitting or lying down, as opposed to cessation of ambulation. In addition, complaints that are experienced upon standing suggest nonvascular causes. When confusion persists, the use of noninvasive vascular laboratory testing modalities, including treadmill exercise, can help establish the diagnosis.

Collateral Arterial Network

The principal collateral pathways in severe aortoiliac artery occlusive disease or chronic aortic occlusion that may provide blood flow distal to the aortoiliac lesion include: (a) the SMA to the distal IMA via its superior hemorrhoidal branch to the middle and inferior hemorrhoidals to the internal iliac artery (39%); (b) the lumbar arteries to the superior gluteal artery to the internal iliac system (37%); (c) the lumbar arteries to the lateral and deep circumflex arteries to the common femoral artery (CFA) (12%); and (d) Winslow’s pathway from the subclavian to the superior epigastric artery to the inferior epigastric artery to the external iliac arteries at the groin (Fig. 7). In general, treatment indications for aortoiliac artery occlusive disease include disabling claudication, ischemic rest pain, nonhealing LE tissue wound, and LE microembolization that arise from aortoiliac lesions.

Fig. 7. Pertinent collateral pathways are developed in the event of chronic severe aortoiliac occlusive disease. As illustrated in this multidetector computed tomography angiography, these collaterals include epigastric arteries (large white arrows), an enlarged inferior mesenteric artery (white arrowhead), and enlarged lumbar arteries (black arrows).

         Disease Classification

Based on the atherosclerotic disease pattern, aortoiliac occlusive disease can be classified into three various types (Fig. 8). Type I aortoiliac disease, which occurs in 5 to 10% of patients, is confined to the distal abdominal aorta and common iliac vessels (Fig. 9). Due to the localized nature of this type of aortic obstruction and formation of collateral blood flow around the occluded segment, limb-threatening symptoms are rare in the absence of more distal disease (Fig. 10). This type of aortoiliac occlusive disease occurs in a relatively younger group of patients (aged in their mid-50s), compared with patients who have more femoropopliteal disease. Patients with a type I disease pattern have a lower incidence of hypertension and diabetes, but a significant frequency of abnormal blood lipid levels, particularly type IV hyperlipoproteinemia. Symptoms typically consist of bilateral thigh or buttock claudication and fatigue. Men report diminished penile tumescence and may have complete loss of erectile function. These symptoms in the absence of femoral pulses constitute Leriche’s syndrome. Rest pain is unusual with isolated aortoiliac disease unless distal disease coexists. Occasionally patients report a prolonged history of thigh and buttock claudication that recently has become more severe. It is likely that this group has underlying aortoiliac disease that has progressed to acute occlusion of the terminal aorta. Others may present with “trash foot” that represents microembolization into the distal vascular bed (Fig. 11).

Fig. 8. Aortoiliac disease can be classified into three types. Type I represents focal disease affecting the distal aorta and proximal common iliac artery. Type II represents diffuse aortoiliac disease above the inguinal ligament. Type III represents multisegment occlusive disease involving aortoiliac and infrainguinal arterial vessels.

 

Fig. 9. Type I aortoiliac disease is confined to the distal abdominal aorta (long arrow) or proximal common iliac arteries. Due to the localized nature of this type of aortic obstruction and formation of collateral blood flow around the occluded segment (short arrows), limb-threatening symptoms are rare in the absence of more distal disease.

 

Fig. 10. Multidetector computed tomography angiography of the aortoiliac artery circulation in a 63-year-old man with buttock claudication. Three-dimensional image reconstruction showing intra-arterial calcification of the aorta (large arrows) and right common iliac artery (small arrows). This is consistent with a type I aortoiliac occlusive disease.

 

Fig. 11. Atherosclerotic disease involving the aortoiliac segment can result in microembolization of the lower leg circulation, resulting in trash foot or digital gangrene of toes.

Type II aortoiliac disease represents a more diffuse atherosclerotic progression that involves predominately the abdominal aorta with disease extension into the CIA. This disease pattern affects approximately 25% of patients with aortoiliac occlusive disease. Type III aortoiliac occlusive disease, which affects approximately 65% of patients with aortoiliac occlusive disease, is widespread disease that is seen above and below the inguinal ligament (Fig. 12). Patients with “multilevel” disease are older, more commonly male (with a male-to-female ratio of 6:1), and much more likely to have diabetes, hypertension, and associated atherosclerotic disease involving cerebral, coronary, and visceral arteries. Progression of the occlusive process is more likely in these patients than in those with localized aortoiliac disease. For these reasons, most patients with a type III pattern tend to present with symptoms of advanced ischemia and require revascularization for limb salvage rather than for claudication. These patients have a decreased 10-year life expectancy when compared to patients with localized aortoiliac disease.

Fig. 12. Type III aortoiliac occlusive disease is a multilevel disease pattern that affects the aortoiliac segment as well as infrainguinal femoropopliteal vessels. Most patients with this disease pattern tend to present with symptoms of advanced ischemia and require revascularization for limb salvage rather than for claudication.

The most commonly used classification system of iliac lesions has been set forth by the TASC II group with recommended treatment options. This lesion classification categorizes the extent of atherosclerosis and has suggested a therapeutic approach based on this classification (Table 3 and Fig. 13). According to this consensus document, endovascular therapy is the treatment of choice for type A lesions, and surgery is the treatment of choice for type D lesions. Endovascular treatment is the preferred treatment for type B lesions, and surgery is the preferred treatment for good-risk patients with type C lesions. In comparison to the 2000 TASC II document, the commission has not only made allowances for treatment of more extensive lesions, but also took into account the continuing evolution of endovascular technology and the skills of individual interventionalists when stating that the patient’s comorbidities, fully informed patient preference, and the local operator’s long-term success rates must be considered when making treatment decisions for type B and type C lesions

Table 3. TASC II Classification of Aortoiliac Occlusive Lesions

 

 

Fig. 13. Schematic depiction of Trans-Atlantic Inter-Society Consensus classification of aortoiliac occlusive lesions

 

General Treatment Considerations

 

There is no effective medical therapy for the management of aortoiliac disease, but control of risk factors may help slow progression of atherosclerosis. Patients should have hypertension, hyperlipidemia, and diabetes mellitus controlled. They should be advised to stop smoking. Most patients are empirically placed on antiplatelet therapy. A graduated exercise program may improve walking efficiency, endothelial function, and metabolic adaptations in skeletal muscle, but, there is usually minimal improvement in patients with aortoiliac disease who are treated with these measures. Failure to respond to exercise and/or drug therapy should prompt consideration for limb revascularization. Patients with buttock claudication and reduced or absent femoral pulses who fail to respond to exercise and drug therapy should be considered for revascularization because they are less likely than patients with more distal lesions to improve without concomitant surgical or endovascular intervention.

 

Surgical Reconstruction of Aortoiliac Occlusive Disease

 

Aortobifemoral Bypass

 

Surgical options for treatment of aortoiliac occlusive diseases consist of various configurations of aortobifemoral bypass (ABF) grafting, various types of extra-anatomic bypass grafts, and aortoiliac endarterectomy. The procedure performed is determined by several factors, including anatomic distribution of the disease, clinical condition of the patient, and personal preference of the surgeon.

In most cases, ABF is performed because patients usually have disease in both iliac systems. Although one side may be more severely affected than the other, progression does occur, and bilateral bypass does not complicate the procedure or add to the physiologic stress of the operation. ABF reliably relieves symptoms, has excellent long-term patency (approximately 70 to 75% at 10 years), and can be completed with a tolerable perioperative mortality (2 to 3%).

 

Technical Considerations for Aortobifemoral Bypass

 

Both femoral arteries are initially exposed to ensure that they are adequate for the distal anastomoses. The abdomen is then opened in the midline, the small intestine is retracted to the right, and the posterior peritoneum overlying the aorta is incised. A retroperitoneal approach may be selected as an alternative in certain situations. This approach involves making a left flank incision and displacing the peritoneum and its contents to the right. Such an approach is contraindicated if the right renal artery is acutely occluded, because visualization from the left flank is very poor. Tunneling of a graft to the right femoral artery also is more difficult from a retroperitoneal approach, but can be achieved. The retroperitoneal approach has been reputed to be better tolerated than midline laparotomy for patients with multiple previous abdominal operations and with severe pulmonary disease. Further proposed advantages of the retroperitoneal approach include less GI disturbance, decreased third-space fluid losses, and ease with which the pararenal aorta can be accessed. There are randomized reports, however, that support and refute the superiority of this approach. A collagen-impregnated, knitted Dacron graft is used to perform the proximal aortic anastomosis, which can then be made in either an end-to-end or end-to-side fashion using 3-0 polypropylene suture. The proximal anastomosis should be made as close as possible to the renal arteries to decrease the incidence of restenosis from progression of the atherosclerotic occlusive process in the future.

An end-to-end proximal aortic anastomosis is necessary in those patients with an aortic aneurysm or complete aortic occlusion extending up to the renal arteries (Fig. 14). Although in theory, the end-to-end configuration allows for less turbulence and less chance of competitive flow with still patent host iliac vessels, there have not been consistent results to substantiate differences in patency between end-to-end and end-to-side grafts. Relative indications for an end-to-side proximal aortic anastomosis include the presence of large aberrant renal arteries, an unusually large IMA with poor back-bleeding, suggesting inadequate collateralization, and/or occlusive disease involving bilateral external iliac arteries. Under such circumstances, end-to-end bypass from the proximal aorta to the femoral level devascularizes the pelvic region because there is no antegrade or retrograde flow in the occluded external iliac arteries to supply the hypogastric arteries. As a result of the pelvic devascularization, there is an increased incidence of impotence, postoperative colon ischemia, buttock ischemia, and paraplegia secondary to spinal cord ischemia, despite the presence of excellent femoral and distal pulses.

 

Fig. 14. In an end-to-end proximal aortic anastomosis, the aorta is divided in half. The proximal end of the aorta is anastomosed to the end of a prosthetic graft while the distal divided aortic stump is oversewn.

 

An end-to-side proximal aortic anastomosis can be associated with certain disadvantages, which include the potential for distal embolization when applying a partially occlusive aortic clamp (Fig. 15). Furthermore, the distal aorta often proceeds to total occlusion after an end-to-side anastomosis. There may also be a higher incidence of aortoenteric fistula following construction of end-to-side proximal anastomoses because the anterior projection makes subsequent tissue coverage and reperitonealization of the graft more difficult. The limbs of the graft are tunneled through the retroperitoneum to the groin, where an end-to-side anastomosis is fashioned between the graft and the bifurcation of the CFA using 5-0 polypropylene suture. Endarterectomy or patch angioplasty of the profunda femoris may be required concurrently. Once the anastomoses have been fashioned and the graft thoroughly flushed, the clamps are removed and the surgeon carefully controls the degree of aortic occlusion until full flow is re-established. During this period the patient must be carefully monitored for hypotension. Declamping hypotension is a complication of sudden restoration of aortic flow, particularly following prolonged occlusion. Once flow has been re-established, the peritoneum is carefully reapproximated over the prosthesis to prevent fistulization into the intestine.

 

Fig. 15. In an end-to-side aortic anastomosis, the end of a prosthetic graft is connected to the side of an aortic incision

 

Despite the presence of multilevel disease in most patients, a properly performed aortobifemoral operation can provide arterial inflow and alleviate claudication symptoms in 70 to 80% of patients; however, 10 to 15% of patients will require simultaneous outflow reconstruction to address distal ischemia and facilitate limb salvage. The advantage of concomitant distal revascularization is avoidance of reoperation in a scarred groin. As a rule, if the profunda femoris can accept a 4-mm probe and if a No. 3 Fogarty embolectomy catheter can be passed distally for 20 cm or more, the PFA will be sufficient for outflow and concomitant distal revascularization is not necessary.

 

Aortic Endarterectomy

 

Aortoiliac endarterectomy is rarely performed, as it is associated with greater blood loss, greater sexual dysfunction, and is more difficult to perform. Long-term patency is comparable with aortobifemoral grafting, and thus it remains a reasonable option in cases in which the risk of infection of a graft is excessive, because it involves no prosthetic tissue. Aortoiliac endarterectomy was useful when disease was localized to either the aorta or CIAs; however, at present, aortoiliac PTA, stents, and other catheter-based therapies have become first-line treatments in this scenario. Endarterectomy should not be performed if the aorta is aneurysmal because of continued aneurysmal degeneration of the endarterectomized segment. If there is total occlusion of the aorta to the level of the renal arteries, aortic transection several centimeters below the renal arteries with thrombectomy of the aortic cuff followed by graft insertion is easier and more expeditious when compared to endarterectomy. Involvement of the EIA makes aortic endarterectomy more difficult to complete because of decreased vessel diameter, increased length, and exposure issues. The ability to establish an appropriate endarterectomy plane is compromised due to the muscular and inherently adherent nature of the media in this location. There is a higher incidence of early thrombosis and late failure with extended aortoiliofemoral endarterectomy when compared to bypass grafting as a result of recurrent stenosis.

 

Axillofemoral Bypass

 

An axillofemoral bypass is an extra-anatomic reconstruction that derives arterial inflow from the axillary artery to the femoral artery. This is a treatment option for those patients with medical comorbidities that prohibit an abdominal vascular reconstruction. It may be performed under local anesthesia and is used for limb salvage. Extra-anatomic bypasses have lower patency when compared to aortobifemoral, and therefore, are seldom recommended for claudication. Before performing this operation, the surgeon should check pulses and BP in both arms to ensure that there is no obvious disease affecting flow through the axillary system. Angiography of the axillosubclavian vasculature is not necessary, but can be helpful if performed at the time of aortography. The axillary artery is exposed below the clavicle, and a 6- to 8-mm externally reinforced PTFE graft is tunneled subcutaneously down the lateral chest wall and lateral abdomen to the groin. It is anastomosed to the ipsilateral distal at the CFA bifurcation into the superficial femoral and profunda femoris arteries. A femorofemoral crossover graft using a 6- to 8-mm externally reinforced PTFE graft is then used to revascularize the opposite extremity if necessary. Reported patency rates over 5 years vary from 30 to 80%. Paradoxically, although it is a less complex procedure than aortofemoral grafting, the mortality rate is higher (10%), reflecting the compromised medical status of these patients.

 

Iliofemoral Bypass

 

One option for patients with unilateral occlusion of the distal common iliac or external iliac arteries is iliofemoral grafting (Fig. 16). Long-term patency is comparable to aortounifemoral bypass and because the procedure can be performed using a retroperitoneal approach without clamping the aorta, the perioperative mortality is less.

 

Fig. 16 A. Skin markings showing the incisions of an iliofemoral bypass

 

 

Fig. 16 B. A prosthetic bypass graft is used for an iliofemoral artery bypass in which the proximal anastomosis is connected to the common iliac artery (long arrow) while the distal anastomosis is connected to the common femoral artery (short arrow).

 

Femorofemoral Bypass

 

A femorofemoral bypass is another option for patients with unilateral stenosis or occlusion of the common or EIA who have rest pain, tissue loss, or intractable claudication. The primary (assisted) patency at 5 years is reported to be 60 to 70%, and, although this is inferior when compared to aortofemoral bypass, there are physiologic benefits, especially for patients with multiple comorbidities, because it is not necessary to cross-clamp the aorta. There are no studies supporting the superiority of unsupported or externally supported PTFE over Dacron for choice of conduit. The fear of the recipient extremity stealing blood from the extremity ipsilateral to the donor limb is not realized unless the donor iliac artery and donor outflow arteries are diseased. Depending on the skills of the interventionalist/surgeon, many iliac lesions classified as TASC II B, C, or D caow be addressed using an endovascular approach, thus obviating the need to perform a femorofemoral bypass. Additionally, femorofemoral bypass can be used as an adjuvant procedure after iliac inflow has been optimized with endovascular methods.

 

Obturator Bypass

 

An obturator bypass is used to reconstruct arterial anatomy in patients with groin sepsis resulting from prior prosthetic grafting, intra-arterial drug abuse, groieoplasm, or damage from prior groin irradiation. This bypass can originate from the CIA, EIA, or uninvolved limb of an ABF. A conduit of Dacron, PTFE, or autologous vein is tunneled through the anteromedial portion of the obturator membrane to the distal superficial femoral or popliteal artery. The obturator membrane must be divided sharply so as to avoid injury to adjacent structures, and care must be taken to identify the obturator artery and nerve that pass posterolaterally. After the bypass is completed and the wounds isolated, the infected area is entered, the involved arteries are débrided to healthy tissue, and vascularized muscle flaps are mobilized to cover the ligated ends. There have been varied results in terms of patency and limb salvage for obturator bypass. Some authors have reported 57% 5-year patency and 77% 5-year limb salvage rates, whereas others have shown a high rate of reinfection and low patency requiring reintervention.

 

Thoracofemoral Bypass

 

The indications for thoracofemoral bypass are (a) multiple prior surgeries with a failed infrarenal aortic reconstruction and (b) infected aortic prosthesis. This procedure is more physiologically demanding than other extra-anatomic reconstructions because the patient must not only tolerate clamping the descending thoracic aorta but also performance of a left thoracotomy. The graft is tunneled to the left CFA from the left thorax posterior to the left kidney in the anterior axillary line using a small incision in the periphery of the diaphragm and an incision in the left inguinal ligament to gain access to the extraperitoneal space from below. The right limb is tunneled in the space of Retzius in an attempt to decrease kinking that is more likely to occur with subcutaneous, suprapubic tunneling. Thoracofemoral bypass has long-term patency comparable to aortofemoral bypass.

 

Complications of Surgical Aortoiliac Reconstruction

 

With current surgical techniques and conduits, early postoperative hemorrhage is unusual and occurs in 1 to 2% of cases. It is usually the result of technical oversight or coagulation abnormality. Acute limb ischemia (ALI) occurring after aortoiliac surgery may be the result of acute thrombosis or distal thromboembolism. The surgeon can prevent thromboembolic events by (a) avoiding excessive manipulation of the aorta, (b) ensuring adequate systemic heparinization, (c) judicious placement of vascular clamps, and (d) thorough flushing before restoring blood flow. Acute thrombosis of an aortofemoral graft limb in the early perioperative period occurs in 1 to 3% of patients.112 Thrombectomy of the graft limb is performed through a transverse opening in the hood of the graft at the femoral anastomosis. With this approach, it is possible to inspect the interior of the anastomosis and pass embolectomy catheters distally to clear the superficial femoral and profunda arteries. Various complications may be encountered following aortoiliac or aortobifemoral reconstruction (Table 4).

Table 4. Perioperative Complications of Aortobifemoral Bypass Grafting

 

Intestinal ischemia following aortic reconstruction occurs in approximately 2% of cases; however, with colonoscopy, mucosal ischemia, which is a milder form, is seen more frequently. The surgeon can identify patients who require concomitant revascularization of the IMA, hypogastric arteries, or mesenteric arteries by examining the preoperative arteriogram for the presence of associated occlusive lesions in the celiac axis, the superior mesenteric arteries, or both. Likewise patients with patent and enlarged IMA or a history of prior colonic resections will benefit from IMA reimplantation.

In a comprehensive review of 747 patients who had aortoiliac operations for occlusive disease, secondary operations for late complications such as reocclusion, pseudoaneurysms, and infection were necessary in 21% of cases over a 22-year period. The most frequent late complication is graft thrombosis. Limb occlusion occurs in 5 to 10% of patients within 5 years of the index operation and in 15 to 30% of patients 10 years or more after the index operation. Anastomotic pseudoaneurysms occur in 1 to 5% of femoral anastomoses in patients with aortofemoral grafts. Predisposing factors to pseudoaneurysm formation include progression of degenerative changes within the host artery, excessive tension at the anastomosis, and infection. Due to the associated risks of thrombosis, distal embolization, infection, and rupture, anastomotic aneurysms should be repaired expeditiously.

Infection following aortoiliac reconstruction is a devastating complication that occurs in 1% of cases. Femoral anastomoses of aortofemoral reconstructions and axillofemoral bypasses are prone to infection. Use of prophylactic antibiotics and meticulous surgical technique are vital in preventing contamination of the graft at the time of implantation. If infection appears to be localized to a single groin, one may consider the treatment strategies of graft preservation, aggressive local wound débridement, antibiotic solution irrigation, and soft tissue coverage with rotational muscle flaps. This nonexcisional treatment approach may be useful in selective cases of localized femoral graft infection. Most patients with infected aortoiliofemoral reconstructions usually require graft excision and revascularization via remote uncontaminated routes or the use of in situ replacement to clear the infective process and maintain limb viability. Aortoenteric fistula and associated GI hemorrhage are devastating complications, with a 50% incidence of death or limb loss. The incidence of aortoenteric fistula formation appears to be higher after an end-to-side proximal anastomosis, because it is more difficult to cover the prosthesis with viable tissue and avoid contact with the GI tract with this configuration. Treatment of aortoenteric fistula requires resection of all prosthetic material, closure of the infrarenal abdominal aorta, repair of the GI tract, and revascularization by means of an extra-anatomic graft.

 

LOWER EXTREMITY ARTERIAL OCCLUSIVE DISEASE

 

The symptoms of LE occlusive disease are classified into two large categories: ALI and chronic limb ischemia (CLI). Ninety percent (90%) of acute ischemias are either thrombotic or embolic. Frequently, sudden onset of limb-threatening ischemia may be the result of acute exacerbation of the pre-existing atherosclerotic disease. Chronic ischemia is largely due to atherosclerotic changes of the LE that manifest from asymptomatic to limb-threatening gangrene. As the population ages, the prevalence of chronic occlusive disease of the LE is increasing and it significantly influences lifestyle, morbidity, and mortality. In addition, multiple comorbid conditions increase risks of surgical procedures. Endovascular interventions become an important alternative in treating LE occlusive disease. However, despite rapid evolving endovascular technology, LE endovascular intervention continues to be one of the most controversial areas of endovascular therapy.

 

Epidemiology

 

In a detailed review of the literature, McDaniel and Cronenwett concluded that claudication occurred in 1.8% of patients under 60 years of age, 3.7% of patients between 60 and 70 years of age, and 5.2% of patients over 70 years of age. Leng and his colleagues scanned 784 subjects using ultrasound in a random sample of men and women ages 56 to 77 years. Of the subjects that were scanned, 64% demonstrated atherosclerotic plaque. However, a large number of patients had occlusive disease without significant symptoms. In a study by Schroll and Munck, only 19% of the patients with peripheral vascular disease were symptomatic. Using ankle-brachial indices (ABIs), Stoffers and colleagues scanned 3171 individuals between the ages of 45 and 75 and identified 6.9 % of patients who had ABIs <0.95, only 22% of whom had symptoms. In addition, they demonstrate that the concomitant cardiovascular and cerebrovascular diseases were three to four times higher among the group with asymptomatic peripheral vascular diseases than those without peripheral vascular disease. Furthermore, they confirm that 68% of all peripheral arterial obstructive diseases were unknown to the primary care physician and this group mainly represented less advanced cases of atherosclerosis. However, among patients with an ABI ratio <0.75, 42% were unknown to the primary physicians.

 

Diagnostic Evaluation

 

The diagnosis of LE occlusive disease often is made based upon a focused history and physical examination, and confirmed by the imaging studies. A well-performed physical examination often reveals the site of lesions by detecting changes in pulses, temperature, and appearances. The bedside ABIs using BP cuff also aid in diagnosis. Various clinical signs and symptoms are useful to differentiate conditions of viable, threatened, and irreversible limb ischemia caused by arterial insufficiency.

Noninvasive studies are important in documenting the severity of occlusive disease objectively. Ultrasound Dopplers measuring ABIs and segmental pressures are widely used in North America and Europe. Normal ABI is >1.0. In patients with claudication, ABIs decrease to 0.5 to 0.9 and to even lower levels in patients with rest pain or tissue loss. Segmental pressures are helpful in identifying the level of involvement. Decrease in segmental pressure between two segments indicates significant disease. Ultrasound duplex scans are used to identify the site of lesion by revealing flow disturbance and velocity changes. A meta-analysis of 71 studies by Koelemay and associates confirmed that duplex scanning is accurate for assessing arterial occlusive disease in patients suffering from claudication or critical ischemia, with an accumulative sensitivity of 80% and specificity of over 95%. Adding an ultrasound contrast agent further increases sensitivity and specificity to ultrasound technology. Other noninvasive imaging technologies such as MRA and CTA are rapidly evolving and gaining popularity in the diagnosis of LE occlusive disease (Figs. 17 and 18).

 

Fig. 17. A high-resolution computed tomography angiography of a patient with normal right lower extremity arterial circulation. Distal occlusive disease is noted in the left tibial arteries (arrow).

 

 

Fig 18 A. A multidetector computed tomographic angiography of a patient with an infrapopliteal arterial circulation

 

 

Fig 18 B. Pedal arterial circulation. The high spatial resolution and image quality of these images show three patent infrapopliteal runoff vessels and patent pedal vessels at the foot level

 

Contrast angiography remains the gold standard in imaging study. Using contrast angiography, interventionists can locate and size the anatomic significant lesions and measure the pressure gradient across the lesion, as well as plan for potential intervention. Angiography is, however, semi-invasive and should be confined to patients for whom surgical or percutaneous intervention is contemplated. Patients with borderline renal function may need to have alternate contrast agents such as gadolinium or carbon dioxide to avoid contrast-induced nephrotoxicity.

 

Differential Diagnosis

 

Arterial insufficiency frequently leads to muscle ischemic pain involving the LE muscularly, particularly during exercise. Intermittent claudication is pain affecting the calf, and, less commonly, the thigh and buttock, which is induced by exercise and relieved by rest. Symptom severity varies from mild to severe. Intermittent claudication occurs as a result of muscle ischemia during exercise caused by obstruction to arterial flow. For differential diagnosis of intermittent claudication, there are a variety of neurologic, musculoskeletal, and venous conditions that may produce symptoms of calf pain (Table 5). Additionally, various non-atherosclerotic conditions also can cause symptoms consistent with intermittent LE claudication (Table 6). Nocturnal calf muscle spasms or night cramps are not indicative of arterial disease. They are common but are difficult to diagnose with certainty. Foot ulceration is not always the result of arterial insufficiency. Ischemic ulcers occur on the toes or lateral side of the foot and are painful. By comparison, venous ulcers, which also are common, occur above the medial malleolus. These venous stasis ulcers are typically surrounded by a peripheral area of darkened skin discoloration that is also known as lipodermatosclerosis. Neuropathic ulcers usually are found on weight-bearing surfaces, have thick calluses, and are pain free. Ulcers may be the result of more than one etiology. Rest pain must be distinguished from peripheral neuropathy, which is prevalent in diabetic patients. Patients with diabetic neuropathy tend to have decreased vibration and position sense and decreased reflexes. Spinal stenosis causes pain that is exacerbated with standing and back extension.

 

Table 5 Differential Diagnosis of Intermittent Claudication

 

Table 6. Non-Atherosclerotic Causes of Intermittent Claudication

 

 

Lower Extremity Occlusive Disease Classification

 

LE occlusive disease may range from exhibiting no symptoms to limb-threatening gangrene. There are two major classifications based on the clinical presentations.

The Fontaine classification uses four stages: Fontaine I is the stage when patients are asymptomatic; Fontaine II is when they have mild (IIa) or severe (IIb) claudication; Fontaine III is when they have ischemic rest pain; and Fontaine IV is when patients suffer tissue loss such as ulceration or gangrene (Table 7).

Table 7 Classification of Peripheral Arterial Disease Based on the Fontaine and Rutherford Classifications

 

The Rutherford classification has four grades (0–III) and seven categories (0–6). Asymptomatic patients are classified into category 0; claudicants are stratified into grade I and divided into three categories based on the severity of the symptoms; patients with rest pain belong to grade II and category 4; patients with tissue loss are classified into grade III and categories 5 and 6, based on the significance of the tissue loss. These clinical classifications help to establish uniform standards in evaluating and reporting the results of diagnostic measurements and therapeutic interventions (see Table 7).

The most clinically useful classification of LE atherosclerotic disease should be based on morphologic characters of the lesions. The TASC II task force published a guideline separating LE arterial diseases into femoropopliteal and infrapopliteal lesions (Table 8). This guideline is particularly useful in determining intervention strategies based on the disease classifications. Based on the guideline, femoropopliteal lesions are divided into four types: A, B, C, and D. Type A lesions are single focal lesions <3 cm in length that did not involve the origins of the superficial femoral artery (SFA) or the distal popliteal artery; Type B lesions are single lesions 3 to 5 cm in length not involving the distal popliteal artery or multiple or heavily calcified lesions <3 cm in length; Type C lesions are multiple stenoses or occlusions >15 cm in length, or recurrent stenoses or occlusions that need treatment after two endovascular interventions. Type D lesions were those with complete occlusion of CFA, SFA, or popliteal artery.

 

Table 8. TASC II Classification of Femoral Popliteal Occlusive Lesions

 

 

In a similar fashion, infrapopliteal arterial diseases are classified into four types based on TASC II guideline (Fig. 19). Type A lesions are single lesions <1 cm in length not involving the trifurcation; Type B lesions are multiple lesions <1 cm in length or single lesions shorter than 1 cm involving the trifurcation; Type C lesions are those lesions extensively involving trifurcation or those that are 1- to 4-cm stenotic or 1- to 2-cm occlusive lesions; Type D lesions are occlusions longer than 2 cm or diffuse diseases.

 

 

Fig. 19. Schematic depiction of Trans-Atlantic Inter-Society Consensus classification of femoral popliteal occlusive lesions

 

Clinical Manifestations of Chronic Limb Ischemia

 

The term chronic limb ischemia is reserved for patients with objectively proven arterial occlusive disease and symptoms lasting for more than 2 weeks. Symptoms include rest pain and tissue loss such as ulceration or gangrene (Table 9). The diagnosis should be corroborated with noninvasive diagnostic tests such as the ABI, toe pressures, and transcutaneous oxygen measurements. Ischemic rest pain most commonly occurs below an ankle pressure of 50 mmHg or a toe pressure <30 mmHg.2 Ulcers are not always of an ischemic etiology (Table 10). In many instances, there are other etiologic factors (traumatic, venous, or neuropathic) that are contributory, but it is underlying peripheral arterial disease (PAD) that may be responsible for delayed or absent healing (Fig. 20). Healing of ulcers requires an inflammatory response and greater perfusion than is required to support intact skin and underlying tissues. As a result, the ankle and toe pressure levels needed for healing are higher than the pressures seen with ischemic rest pain. For patients with ulcers or gangrene, the presence of CLI is suggested by an ankle pressure <70 mmHg or a toe systolic pressure <50 mmHg.2 It is important to understand that there is no definite consensus regarding the vascular hemodynamic parameters required to make the diagnosis of CLI.

Table 9. Clinical Categories of Chronic Limb Ischemia

Table 10. Symptoms and Signs of Neuropathic Ulcer versus Ischemic Ulcer

 

 

 

Fig. 20 A A neuropathic ulcer is characterized by a punched-out appearance with loss of sensation in the surrounding skin. The foot may be warm to touch, and pulses may be present in the distal pedal arteries

 

 

Fig. 20 B An ischemic ulcer is characterized by a gangrenous skin change in the foot or toes. The foot is usually cold to touch with absent pedal pulses. The foot is painful to touch with decreased distal capillary refills.

 

One of the most common sites for occlusive disease is in the distal SFA as it passes deep through the adductor canal. It may be that the entrapment by the adductor hiatus prevents the compensatory dilation that occurs in atherosclerotic vessels. Stenoses, which develop here, progress to occlusion of the distal third of the SFA (Fig. 21). When distal SFA occlusion develops slowly, it may be totally asymptomatic because of development of collaterals from the proximal SFA or the profunda femoris artery (PFA) can bypass the occlusion and reconstitute the popliteal artery. Symptom development is a function of the extent of occlusion, adequacy of collaterals, and also the activity level of the patients.

 

 

Fig. 21. Computed tomography angiogram of a patient with an occluded left superficial femoral artery (single long arrow) with reconstituted superficial femoral artery at the level of midthigh. Diffuse arterial calcifications (double small arrows) are noted in the mid and distal left superficial femoral arteries.

 

Presenting symptoms of femoropopliteal occlusive disease are broadly classified into two types: limb-threatening and non–limb-threatening ischemia. Claudication is non–limb-threatening, while rest pain, ulceration, and gangrene are limb-threatening and warrant urgent intervention. Occlusive disease of the femoral artery may be isolated or occur in conjunction with multilevel disease that involves both the aortoiliac segment and the tibial vessels. Symptoms in patients with multilevel disease are more severe than in those with single-level disease. Pain from isolated SFA and popliteal occlusion typically manifests as calf claudication. Cramping pain develops in the calf on ambulation, occurs at a reproducible distance, and is relieved by rest. Activities such as climbing stairs or going uphill also exacerbate the pain. Many patients report worsening symptoms during cold weather. It is important to evaluate whether the symptoms are progressive or static. In >70% of patients, the disease is stable, particularly with risk factor modification.

Progression of the underlying atherosclerotic process is more likely to occur in patients with diabetes, those who continue to smoke, and those who fail to modify their atherosclerotic risk factors. In comparison, rest pain is constant, and usually occurs in the forefoot across the metatarsophalangeal joint. It is worse at night and requires placing the foot in a dependent position to improve symptoms. Patients may report that they either sleep in a chair or hang the foot off the side of the bed. The pain is severe and relentless, even with narcotics. Ischemic ulceration most commonly involves the toes. Any toe can be affected. Occasionally, ulcers develop on the dorsum of the foot. Ulceration can occur in atypical positions in an ischemic foot from trauma such as friction from poorly fitting shoes. Injury to a foot with borderline ischemia can convert an otherwise stable situation into one that is limb-threatening. The initial development of gangrene commonly involves the digits. As with all vascular patients, it is important to evaluate their risk factors, intercurrent cardiac diseases, and any prior vascular interventions.

 

Treatment Considerations for Chronic Limb Ischemia

 

Patients with vascular diseases frequently have complicated medical comorbidities. Careful patient evaluation and selection should be performed for any peripheral arterial vascular procedure. The fundamental principle is to assess not only the surgical risk from the peripheral arterial system but also the global nature of the atherosclerotic process. Full cardiac evaluations are ofteecessary due to the high incidence of concomitant atherosclerotic coronary arteries disease, resulting in a high risk for ischemic events. Hertzer and associates reviewed coronary angiographies on 1000 patients undergoing elective vascular procedures and identified 25% of concomitant correctable CAD, including 21% in patients undergoing elective peripheral vascular intervention. Conte and associates analyzed their 20-year experience in a tertiary practice setting in 1642 open LE reconstructive surgeries and concluded that patients requiring LE reconstruction presented an increasingly complex medical and surgical challenge compared with the previous decade. With aging of the population, there are a growing number of vascular patients who have prohibitive medical comorbidities that are deemed high-risk for open surgical repair. Endovascular intervention provides an attractive alternative.

As for open surgical repair, the clinical indications for endovascular intervention of LE PADs include lifestyle-limiting claudication, ischemic rest pain, and tissue loss or gangrene. Importantly, endovascular procedures should be performed by a competent vascular interventionist who understands the vascular disease process and is familiar with a variety of endovascular techniques. In addition, certain lesions such as long segment occlusion, heavily calcified lesion, orifice lesion, or lesions that can be not be traversed by a guidewire may not be amendable to endovascular treatment or may be associated with poor outcomes. A proper selection of patients and techniques is critical in achieving a good long-term outcome.

Endovascular intervention for LE occlusive disease is continuously evolving. Success and patency rates of endovascular intervention are closely related to the anatomic and morphologic characters of the treated lesions. The TASC II work group made recommendations on the intervention strategies of LE arterial diseases based on the morphologic characters. Based on the TASC II guidelines, endovascular treatment is recommended for type A lesions, open surgery is recommended for Type D lesions, and no recommendations were made for Types B and C lesions. However, with rapid advancement in endovascular technologies, there are increased numbers of lesions amendable to endovascular interventions.

There is less literature support on infrapopliteal endovascular intervention due to higher complication and lower success rates. The treatment is restricted to patients with limb-threatening ischemia who lack surgical alternatives. However, with further advancement of endovascular technology and the development of new devices, endovascular intervention will become an integral part of treatment (Table 11). By itself or combined with open technique, percutaneous intervention plays an important role in therapeutic options for LE occlusive disease. As described by the TASC II guidelines, four criteria should be measured to evaluate the clinical success of the treatment: improvement in walking distance, symptomatic improvement, quality of life, and overall graft patency. These criteria should all be carefully weighed and evaluated for each individual before endovascular therapy.

 

Table 11. Summary of Endovascular Treatment Strategies Using Device-Based Infrapopliteal Intervention

 

 

Endovascular Treatment

 

Technical Considerations

 

A sterile field is required in either an OR or an angiography suite with image capability. The most common and safest access site is the CFA via either a retrograde or antegrade approach. For diagnostic angiography, arterial access should be contralateral to the symptomatic sides. For therapeutic procedures, location of the lesion and the anatomic structures of the arterial tree determine the puncture site. To avoid puncturing the iliac artery or SFA, the femoral head is located under the fluoroscopy and used as the guide for the level of needle entry. In addition, there are several useful techniques in helping access a pulseless CFA, including puncturing guided by ultrasound, using a micropuncture kit, and targeting calcification in a calcified vessel. An antegrade approach may be challenging, particularly in obese patients. Meticulous technique is crucial in preventing complications, and a bony landmark can be used as guidance to ensure CFA puncture.

Traversing the lesion with a wire is the most critical part of the procedure. Typically, 0.035-in guidewires are used for femoropopliteal lesions and 0.014- or 0.018-in guidewires are used for infrapopliteal access. Hydrophilic-coated wires, such as Glide wires, are useful iavigating through tight stenosis or occlusion. An angled-tip wire with a torque device may be helpful in crossing an eccentric lesion, and a shaped selective catheter is frequently used in helping manipulate the wire across the lesion. The soft and floppy end of the wire is carefully advanced, crossing the lesion under fluoroscopy, and gentle force is applied while manipulating the wire. Once the lesion has been traversed, one needs to pay particular attention to the tip of the wire to ensure a secure wire access and avoid vessel wall perforation or dissection.

Once the access to the diseased vessel is secured and the wire has successfully traversed the lesion, several treatment modalities can be used either used alone or in conjunction with others, including angioplasty, stent or stent graft placement, and atherectomy. The available angioplasty techniques are balloon angioplasty, cryoplasty, subintimal angioplasty (SA), and cutting balloon. The most commonly used atherectomy techniques include percutaneous atherectomy catheter and laser atherectomy device.

Systemic anticoagulation should be maintained routinely during LE arterial interventions to minimize the risk of pericatheter thrombosis. Unfractionated heparin is the most commonly used agent, given on a weight-based formula. It is a common clinical practice to use a 80 to 100 mg/kg initial bolus for a therapeutic procedure to achieve the activated clotting time above 250 seconds on the catheter insertion and subsequently 1000 units for each additional hour of the procedure. Newer agents such as low molecular weight heparin, platelet IIb/IIIa inhibitor, direct thrombin inhibitor, or recombinant hirudin have been available and can be used either alone or in conjunction with heparin, particularly in patients sensitive to unfractionated heparin. After procedures, all patients are placed on antiplatelet therapy such as aspirin. Additional antiplatelet agents such as clopidogrel (Plavix) are given to selected patients with stent placement for at least 6 weeks after LE interventions, unless otherwise contraindicated.

 

Percutaneous Transluminal Balloon Angioplasty

 

After the lesion is crossed with a wire, an appropriate balloon angioplasty catheter is selected and tracked along the wire to traverse the lesion. The length of the selected catheter should be slightly longer than the lesion and the diameter should be equal to the adjacent normal vessel. The balloon tends to be approximately 10 to 20% oversized. The radiopaque markers of the balloon catheter are placed so that they will straddle the lesion. Then, the balloon is inflated with saline and contrast mixture to allow visualization of the insufflation process under the fluoroscopy (Fig. 22). The patient may experience mild pain, which is not uncommon. However, severe pain can be indicative of vessel rupture, dissection, or other complications. An angiography is crucial in confirming the intraluminal location of the catheter and absence of contrast extravasation. The inflation is continued until the waist of the atherosclerotic lesion disappears and the balloon is at full profile. Frequently, several inflations are required to achieve full profile of the balloon (Fig. 23). Occasionally, a lower profile balloon is needed to predilate the tight stenosis so that the selected balloon catheter can cross the lesion.

Fig. 22 A. Angiogram demonstrating a focal stenosis in the superficial femoral artery (arrow).

 

 

Fig. 22 B. This lesion was treated with a balloon angioplasty catheter that inflated a dilating balloon and expanded the flow lumen

 

 

 

Fig. 22 C. Completion angiogram demonstrating satisfactory radiographic result.

 

 

Fig. 23 A. Angiogram demonstrating a segmental occlusion in the distal superficial femoral artery (single arrow).

 

 

Fig. 23 B. This lesion was treated with cryoplasty, which lowered the balloon catheter temperature to a temporary freezing state during the balloon angioplasty procedure (double arrows)

 

 

Fig.23 C. Completion angiogram demonstrated satisfactory result with no evidence of vessel dissection.

 

Besides length and diameter, the operators need to be familiar with several balloon characters. Noncompliant and low-compliant balloons tend to be inflated to their preset diameter and offer greater dilating force at the site of stenosis. Low-compliant balloons are the mainstay for peripheral intervention. A balloon with a low profile is used to minimize complication at the entry site and for crossing the tight lesions. Upon inflation, most balloons do not rewrap to their preinflation diameter and assume a larger profile. Furthermore, trackability, pushability, and crossability of the balloon should be considered when choosing a particular type. Lastly, shoulder length is an important characteristic when performing PTA to avoid injury to the adjacent arterial segments. After PTA, a completion angiogram is performed while the wire is still in place. Leaving the wire in place provides access for repeating the procedure if the result is unsatisfactory.

PTA is an established and effective therapy for select patients with LE occlusive diseases. Studies have shown that PTA of the femoropopliteal segment achieved over a 90% technical success rate and a 38 to 58% 5-year primary patency rate. However, efficacy of PTA is highly dependent upon anatomic selection and patient condition. PTA of lesions longer than 7 to 10 cm offer limited patency, while PTA of shorter lesions, such as those that are <3 cm, have fairly good results. Lofberg and associates performed 127 femoropopliteal PTA procedures and reported a primary 5-year success rate of 12% in limbs with an occlusion longer than 5 cm vs. 32% in limbs with an occlusion <5 cm in length.151 Occlusive lesions have much worse initial technical success rates than stenotic lesions. Concentric lesions respond better to PTA than eccentric lesions, and heavy calcifications have a negative impact on success rates. A meta-analysis by Hunink and associates showed that adjusted 5-year primary patencies after angioplasty of femoropopliteal lesions varied from 12 to 68%, the best results being for patients with claudication and stenotic lesions. Distal runoff is another powerful predictor of long-term success. Johnston analyzed 254 consecutive patients who underwent femoral and popliteal PTA and reported that 5-year patency rates of 53% for stenotic lesions and 36% for occlusive lesions in patients with good runoffs vs. a 5-year patency of 31% for stenotic lesions and 16% for occlusive lesions in patients with poor runoff. Literature reviews showed that 5-year patency rates varied from 27 to 67% based on the runoff statuses.

Due to limited success with infrapopliteal PTA, the indication for infrapopliteal artery PTA is stringent, reserved for limb salvage. Current patency rates from infrapopliteal PTA can be improved further by proper patient selection, ensuring straight-line flow to the foot in at least one tibial vessel, and close patient surveillance for early reintervention. Possible future advances including the use of drug-eluting stents (DES), cutting balloons, and atherectomy devices are being investigated to improve clinical outcomes following endovascular interventions on the tibial arteries. Varty and associates reported a 1-year limb salvage rate of 77% in patients with critical ischemia who underwent infrapopliteal PTA. In patients with favorable anatomies, a 2-year limb salvage rate after infrapopliteal artery PTA is expected to exceed 80 %.

 

Subintimal Angioplasty

 

The technique of SA was first described in 1987 when successful establishment of flow was made by accidental creation of a subintimal channel during treatment of a long popliteal artery occlusion. SA is recommended for chronic occlusion, long segments of lesion, and heavily calcified lesions. In addition, this technique is applicable for vessels with diffuse diseases and for vessels that had previously failed an intraluminal approach because it is difficult to negotiate the wire across the entire diseased segment without dissection.

The principle of this technique is to bypass the occlusion by deliberately creating a subintimal dissection plan commencing proximal to the lesion and continuing in the subintimal space before breaking back into the true lumen distal to the lesion. The occluded lumen is recanalized through the subintimal plan. SA can be performed through either ipsilateral antegrade or contralateral retrograde using the CFA approach. If selecting contralateral CFA puncture, a long guiding sheath is placed across the aortic bifurcation to provide access for the femoropopliteal and infrapopliteal vessels. The subintimal dissection is initiated at the origin of an occlusion by directing the tip of an angled guidewire, usually an angled hydrophilic wire such as Glidewire. A supporting catheter is used to guide the tip of the guidewire away from the important collaterals. When the wire is advanced, a loop is naturally formed at the tip of the guidewire. Once the subintimal plan is entered, the wire tends to move freely in the dissection space. Subintimal location of the wire and the catheter can be confirmed by injecting a small amount of diluted contrast. At this point, the wire and the catheter are then advanced along the subintimal plan until the occlusion segment is passed. A loss of resistance is often encountered as the guidewire re-enters the true lumen distal to the occlusion. Recanalization is confirmed by advancing the catheter over the guidewire beyond the point of re-entry and obtaining an angiogram. This is followed by a balloon angioplasty. To confirm the patency following balloon dilatation, a completion angiogram is performed before withdrawing the catheter and wire. If flow is impaired, repeat balloon dilatation may be necessary. Frequently, a stent is required to maintain a patent lumen and treat residual stenosis if more than a 30% luminal reduction is confirmed on completion angiogram.

Multiple studies have demonstrated the efficacy of SA. Bolia and his colleagues and London and his colleagues reported their extensive experiences on SA for treating long segment occlusions of infrainguinal vessels. They achieved a technical success rate of over 80% for both femoropopliteal and tibial arteries. One-year patency rates varied from 53% for infrapopliteal vessels to 71% for femoropopliteal segments. Limb salvage rates reached over 80% at 12 months. They also reported that the factors influencing patency are smoking, number of runoff vessels, and occlusion length. Studies by other groups showed similar results. Treiman and colleagues treated 25 patients with 6- to 18-cm femoropopliteal occlusion and achieved a technical success rate of 92% and a 12-month primary patency rate of 92%, while Lipsitz and associates reported a technical success rate of 87% in treating 39 patients and achieved a 12-month cumulative patency rate of 74%. Additionally, Ingle and associates reported a technical success rate of 87% on 67 patients with femoropopliteal lesions and a 36-month limb salvage rate of 94%. As demonstrated herein, although technical success rates are similar in most series, the patency rates vary widely in different studies. Patient selection, anatomic character, and lesion locations may account for the wide range of outcomes.

 

Stent Placement

 

Although suggested by Dotter during the late 1960s, the use of an endoluminal stent was not pursued until the limitations of PTA were widely recognized. There are several situations where stent placement is appealing. The primary indication is the potential salvage of an unacceptable angioplasty result. Stent placement is typically used when residual stenosis after PTA is 30% or greater. An endoluminal stent is also used for dissection, perforation, and other PTA complications. Primary stent placement has become a viable alternative for treating ulcerative lesions that may potentially be the source for embolization. Primary stent is also used to treat occlusive lesions that have a tendency of reocclusion and distal embolization after PTA. In addition, an endoluminal stent is potentially beneficial for early restenosis post-PTA. DESs are currently under investigation in the United States and may be promising in decreasing restenotic rates.

Even though technical success rates are high, a published series on femoropopliteal artery stents show that patency rates are comparable to PTA alone with primary patency rates varying from 18 to 72% at 3 years. Gray and associates stented 58 limbs after suboptimal PTA for long SFA lesions and demonstrated a 1-year primary patency rate of 22%. However, Mewissen treated 137 limbs using self-expanding SMART nitinol stents in patients with TASC II A, B, and C femoropopliteal lesions and reported a 1-year primary patency rate of 76% and a 24-month primary patency rate of 60%. Appropriate patient selection and the anatomic characteristics of the lesions are crucial in the success of treatment outcomes. Additionally, stent characteristics may contribute to the patency rate.

Several clinical studies have demonstrated the significant improvements of the new generation of nitinol stents for the SFA lesions: the German Multicenter Experience, the Mewissen trial, the BLASTER Trial, and the SIROCCO trials.161 The German Multicenter Experience was a retrospective review of 111 SFA stenting procedures and found the 6-month patency rates for Smart stents and Wall stents were 82% and 37%, respectively. The BLASTER (Bilateral Lower Arterial Stenting Employing Reopro) Trial evaluated the feasibility of using nitinol stents with and without IV abciximab for the treatment of femoral artery disease. Preliminary results showed a 1-year clinical patency rate of 83%.

Furthermore, DESs, which proved effective at decreasing restenosis in coronary intervention, may offer another promising alternative in LE diseases. The drug, released over a period of time, interferes with smooth muscle cell proliferation, the main cellular element and source of extracellular-matrix–producing restenosis. The first DES clinical trial used Cordis Cypher SMART stents coated with sirolimus (SIROCCO trial). The SIROCCO results showed binary inlesion restenosis rates of 0% in the sirolimus-eluting group vs. 23.5% in the noneluting group at 6-month follow-up angiography.

 

Stent Graft

 

The concept of endobypass using stent graft in treating atherosclerotic SFA disease has been entertained. A stent graft is placed percutaneously across a long segment or multiple segments of lesions and is used to create a femoropopliteal bypass. Theoretically, endobypass has the potential of being as successful as surgical bypass graft by relining the vessel wall in its anatomical position without the negative impact of anastomosis. Stent grafts can be divided into two categories: unsupported and fully supported. The unsupported grafts consist of segments of bypass graft, such as PTFE, with an expandable stent at one or both ends. The unsupported grafts are flexible with a low profile, but prone to external compression. The supported stent grafts consist of a metallic skeleton covered with graft fabric. The presence of a dense metal skeleton promotes an extensive inflammatory response and increases the risk of thrombosis. There is no FDA-approved stent graft for peripheral intervention. However, Viabahn (WL Gore, Calif) is the most commonly used device in the United States, composed of an ultrathin PTFE graft externally supported by a self-expanding nitinol meshwork. The Viabahn device has a specific delivery mechanism—pulling back the attached string—which results in a proximal-to-distal delivery of the endoprosthesis.

Although it is an intriguing concept, data on endobypass results are limited and the graft thrombosis rate is high. Additionally, covering major collateral vessels can potentially jeopardize the viability of the limb if stent graft occlusion occurs. Bauermeister treated 35 patients with Hemobahn and reported a 28.6% occlusion rate on an average 7-month follow-up. Kedora and colleagues recently conducted a prospective, randomized study comparing covered PTFE/nitinol self-expanding stent grafts with prosthetic above-the-knee femoropopliteal bypass. Fifty limbs were randomized into each group. Primary patency at 1-year was approximately 74% for both cohorts, with a mean follow-up of 18 months. The covered nitinol PTFE stent graft in the SFA had a 1-year patency rate comparable to surgical bypass, with a significantly shorter hospital stay (0.9 vs. 3.1 days).

 

Atherectomy

 

The basic principle of atherectomy is to remove the atheroma from obstructed arterial vessels. There are currently five atherectomy devices approved by the FDA: Simpson AtheroCath (DVI, Redwood City, Calif), Transluminal Extraction Catheter (Interventional Technologies, San Diego, Calif), Theratec recanalization arterial catheter (Trac-Wright), Auth Rotablator (Heart Technologies, Redmond, Wash), and SilverHawk system (FoxHollow Technologies, Redwood City, Calif). These devices either cut and remove or pulverize the atheroma plaques.

The Simpson AtheroCath has a directional cutting element that is exposed to one third of the circumference of the arterial wall. The atheroma protruding into the window is excised and pushed into the collection chamber. The Transluminal Extraction Catheter has an over-the-wire, nondirectional cutter mounted on the distal end of a torque tube. The excised atheroma is simultaneously removed by aspiration through the torque tube. The Theratec recanalization arterial catheter is a nondirectional, noncoaxial, atheroablative device. The rotating cam tip pulverizes the atheromatous lesion into minute particles. The Auth Rotablator is a nondirectional, coaxial, atheroablative device with a metal burr embedded with fine diamond chips. Lastly, the SilverHawk device, approved by the FDA for peripheral use in 2003, is a monorail catheter designed to overcome the drawback of direction atherectomy catheter, such as the Simpson AtheroCath. The working end consists of a hinged housing unit containing a carbide cutting blade. The blade is activated from the motor drive unit and the catheter is then advanced through the length of the lesion. Once each pass is completed, the cutter then packs the tissue into the distal end of the nosecone to maximize collection capacity. The SilverHawk can then either be removed or torqued to treat a different quadrant in the same lesion or other lesions.

Despite the promising early technical and clinical success, the mid- and long-term results have been disappointing due to a high incidence of restenosis. However, a multicenter clinical registry of plaque atherectomy in patients with femoropopliteal occlusive disease showed potential clinical efficacy of this technology as the 6- and 12-month rates of survival free of target lesion revascularization were 90 and 80%, respectively. Importantly, nearly three fourths (73%) of patients treated with plaque excision modality did not require adjunctive endovascular therapy as infrainguinal stenting was necessary in only 6.3% of lesions. Results from the TALON registry support the role of plaque excision in selective patients with LE arterial disease.

 

Laser Atherectomy

 

Since laser atherectomy was reported in the 1960s, a variety of innovative approaches have been developed in an effort to overcome the limitation of laser angioplasty. Recent developments in excimer laser technology have led to increased optimism regarding the ability to safely deliver laser energy. Excimer laser atherectomy approved by the FDA for peripheral artery intervention uses precision laser energy control (shallow tissue penetration) and safer wavelengths (ultraviolet as opposed to the infrared spectra in older laser technology), which decreases perforation and thermal injury to the treated vessels.

A laser atherectomy catheter, with diameters varying from 0.9 mm to 2.5 mm, is tracked over the guidewire to the desired target. Once activated, the excimer laser uses ultraviolet energy to ablate the lesion and create a nonthrombogenic arterial lumen. This lumen is further dilated by an angioplasty balloon. Because the excimer laser can potentially reduce the rate of distal embolization by evaporating the lesion, it may be used as an adjunct tool for ostial lesions and lesions that can be traversed by a wire but not an angioplasty balloon catheter.

Several studies regarding the use of excimer laser atherectomy combined with balloon angioplasty on LE occlusive disease have shown promising clinical outcomes. Peripheral excimer laser angioplasty trials involved 318 patients with chronic SFA occlusion. They achieved a technical success rate of 83.2%, a 1-year primary patency rate of 33.6%, and an assisted primary patency rate of 65%.168 Steinkamp and his colleagues treated 127 patients with long-segment of popliteal artery occlusion using laser atherectomy followed by balloon angioplasty and reported a 3-year primary patency rate of 22%. The multicenter clinical trial evaluating the use of laser angioplasty for critical limb ischemia supports the efficacy of this treatment modality in selective patients as the 6-month primary patency rate and clinical improvement were 33 and 89%, respectively.

 

 

Complications of Endovascular Interventions

 

Angioplasty-Related Complications

 

Complications related to PTA vary widely, including dissection, rupture, embolization, pseudoaneurysms, restenosis, hematoma, and acute occlusion secondary to thrombosis, vasospasm, or intimal injury. Clark and associates analyzed the data from 205 patients in the SCVIR Transluminal Angioplasty and Revascularization registry and reported a complication rate of 7.3% for patients undergoing femoropopliteal angioplasty. Minor complications accounted for 75% of the cases, including distal emboli (41.7%), puncture site hematomas (41.7%), contained vessel rupture (8.3%), and vagal reactions (8.3%). In another study, Axisa and colleagues reported an overall rate of significant complications for patients undergoing PTA of the lower extremities as 4.2%, including retroperitoneal bleeding (0.2%), false aneurysm (0.2%), ALI (1.5%), and vessel perforation (1.7%).

Complications limiting the application of SA are parallel to those of PTA. A study investigating the use of SA in 65 patients with SFA occlusion found that complications developed in 15% of patients. These complications included significant stenosis (44%), SFA rupture (6%), distal embolization (3%), retroperitoneal hemorrhage (1.5%), and pseudoaneurysm (1.5%). Additional complications reported consist of perforation, thrombosis, dissection, and extensions beyond the planned re-entry site. Importantly, damage to significant collateral vessels may occur in 1 to 1.5% of patient who undergo SA. If a successful channel is not achieved in this situation, the patient may have a compromised distal circulation that necessitates distal bypass. Cryoplasty is a modified form of angioplasty, and long-term results on LE intervention are not yet available. Fava and associates treated 15 patients with femoropopliteal disease and had a 13% complication rate involving guidewire dissection and PTA-induced dissection of a tandem lesion remote to the cryoplasty zone.

 

Endoluminal Stent and Stent Graft–Related Complications

 

In addition to the aforementioned complications with angioplasty, endoluminal stents are associated with the risk of stent fraction and deformity. The adductor canal has nonlaminar flow dynamics, especially with walking. The forces exerted on the SFA include torsion, compression, extension, and flexion. These forces exert significant stress on the SFA and stents. In addition, the LE is subject to external trauma, which further increases the risk of stent deformity and fracture (Fig. 24). The SIROCCO study showed that stent fracture, although not associated with clinical symptoms, occurs in 18.2% of the procedures involving both the DES and control stent.

 

Fig. 24. Due to various geometric forces, including torsion, compression, extension, and flexion, which exert on the superficial femoral artery, stent fracture (arrows) is a known complication following superficial femoral artery stent placement.

 

Stent grafts may present an additional complication of covering important collaterals, which results in compromised distal circulation. A prospective study evaluating Hemobahn stent grafts in the treatment of femoropopliteal arterial occlusions demonstrated a 23% immediate complication rate, including distal embolization (7.7%), groin hematoma (13.5%), and arteriovenous fistula (1.9%).175

Atherectomy-Related Complications

Overall complication rates associated with atherectomy range from 15.4 to 42.8% and include spasm, thrombosis, dissection, perforation, distal emboli, no reflow, and hematoma. Jahnke and associates conducted a prospective study evaluating high-speed, rotational atherectomy in 15 patients with infrapopliteal occlusive disease. They yielded a 94% technical success rate, which was complicated by vessel rupture (5%), distal embolization (5%), and arterial spasm (5%). Although the excimer laser atherectomy reduces embolic events by evaporating the lesion, embolization still remains a problematic complication. Studies show that distal embolic events occur in 3 to 4% of procedures, and perforation in 2.2 to 4.3% of cases. Other complications compromising laser atherectomy therapy include acute reocclusion, vasospasm, direct vessel injury, and dissection.

 

SURGICAL TREATMENT FOR CHRONIC LIMB ISCHEMIA DUE TO FEMOROPOPLITEAL DISEASE

 

Endarterectomy

 

Endarterectomy has a limited, albeit important, role in LE occlusive disease. It is most frequently used when there is disease in the CFA or involving the PFA. In this procedure, the surgeon opens the diseased segment longitudinally and develops a cleavage plane within the media that is developed proximally and distally. This permits the inner layer containing the atheroma to be excised. Great care must be taken at the distal end of the endarterectomy to ensure either a smooth transition or to tack down the distal endpoint to prevent the flow from elevating a potentially occlusive atheromatous flap. Currently, there is essentially no role for long open endarterectomy in the treatment of SFA stenoses or occlusions. The high incidence of restenosis is what limits use of endarterectomy in this location. Short-segment stenoses are more appropriately treated with balloon angioplasty. Endarterectomy using a catheter-based approach (e.g., Moll endarterectomy device) supplemented with stent grafting or stenting across the endpoint of the endarterectomy is currently being re-evaluated; however, no long-term data are available.

 

Bypass grafting

 

Bypass grafting remains the primary intervention for LE occlusive disease. The type of bypass and conduit are important variables to consider. Patients with occlusive disease limited to the SFA, who have at least 4 cm (ideally 10 cm) of normal popliteal artery reconstituted above the knee joint and at least one continuous vessel to the foot, can be treated with an above-knee (AK) femoropopliteal bypass graft. Despite the fact that in this above-knee location, the differential patencies between prosthetic (PTFE) and vein graft are comparable; undoubtedly, it remains ideal to use a saphenous vein as the bypass conduit, if possible. Saving the vein for future coronary artery bypass or distal leg bypass grafting has been shown to be a flawed argument. One must also take into consideration that the consequences to the vascular outflow after a thrombosed prosthetic are worse than after a thrombosed vein graft.

When the disease extends to involve the popliteal artery or the tibial vessels, the surgeon must select an appropriate outflow vessel to perform a bypass. Suitable outflow vessels are defined as uninterrupted flow channels beyond the anastomosis into the foot. In order of descending preference, they are: AK popliteal artery, below-knee (BK) popliteal artery, posterior tibial artery, anterior tibial artery, and peroneal artery. In patients with diabetes, it is frequently the peroneal artery that is spared. Although the peroneal artery has no direct flow into the foot, collateralization to the posterior tibial and anterior tibial arteries makes it an appropriate outflow vessel. There is no objective evidence to preferentially select tibial over peroneal arteries if they are vessels of equal caliber and quality. The dorsalis pedis, which is the continuation of the anterior tibial in the foot, is frequently spared from atherosclerotic disease and can be used as a target for distal bypasses. Patency is affected by the length of the bypass (longer bypasses have reduced patency), quality of the recipient artery, extent of runoff to the foot, and quality of the conduit (saphenous vein/graft). Five-year assisted patency rates for infrapopliteal venous bypasses are 60%. Venous conduits also have been shown to be suitable for bypasses to plantar arteries. In this location, venous conduits have a 3-year limb salvage of 84% and a 3-year secondary patency of 74%. A meta-analysis suggests unsatisfactory results when PTFE-coated grafts are used to bypass to infrapopliteal arteries. In this location, prosthetic grafts have a 5-year primary patency rate of 30.5%. Additionally, due to distal embolization and compromise of outflow vessels, prosthetic graft occlusion may have more severe consequences than vein graft occlusion.

Two techniques are used for distal bypass grafting: reversed saphenous vein grafting and in situ saphenous vein grafting. There is no difference in outcomes (patency or limb salvage) between these techniques. In the former, the vein is excised in its entirety from the leg using open or endoscopic vein harvest, reversed to render the valves nonfunctional, and tunneled from the CFA inflow to the distal target vessels. End-to-side anastomoses are then created.

Several adjunctive techniques have been tried to improve the patency of bypass grafts to tibial arteries. Creation of an arteriovenous fistula at the distal anastomosis is one option, but it has not been shown to improve patency. Another method involves creating various configurations of vein cuffs or patches at the distal anastomosis in an attempt to streamline the flow and to reduce the likelihood of neointimal hyperplasia. Results with this approach are more promising, especially when done to improve patency of a below-the-knee prosthetic; however, there are no definitive comparative trials that support the superiority of one configuration over another.

 

Amputation

 

Primary amputation is defined as an amputation that is performed without a prior attempt at surgical or endovascular revascularization. It is rarely necessary in patients who, as a result of neglect, present with class III ALI. Primary amputation may play a role in patients with critical limb ischemia who are deemed nonambulatory because of knee contractures, debilitating strokes, or dementia.

 

COMPLICATIONS OF SURGICAL RECONSTRUCTION

 

Vein Graft Stenoses

 

Fifteen percent of vein grafts will develop intrinsic stenoses within the first 18 months following implantation. Consequently, patients with a vein graft were entered into duplex surveillance protocols (scans every 3 months) to detect elevated (>300 cm/s) or abnormally low (<45 cm/s) graft velocities early. Stenoses greater than 50%, especially if associated with changes in ABI, should be repaired to prevent graft thrombosis. Repair usually entails patch angioplasty or short-segment venous interposition, but PTA/stenting is an option for short, focal lesions. Grafts with stenoses that are identified and repaired before thrombosis have assisted primary patency identical to primary patency, whereas a thrombosed autogenous bypass has limited longevity, resulting from ischemic injury to the vein wall. Secondary patency is markedly inferior to primary assisted patency. The recommendation for routine duplex ultrasound surveillance of autogenous infrainguinal bypasses was recently brought into question by a randomized, controlled trial that demonstrated no cost benefit or quality-of-life improvement after 18 months in patients with femoropopliteal venous bypasses. Many surgeons continue with programs of vein graft surveillance, as has been suggested in older trials, awaiting further confirmation of the findings from the more recent study. When intervening on a failing infrainguinal bypass, the original indication for surgery is an important consideration. Limb salvage rates for occluded grafts are better if the indication for the original bypass was claudication rather than rest pain or tissue loss. An acutely occluded infrainguinal graft (≤30 postoperative days) has a 25% limb salvage rate.

 

Limb Swelling

 

Limb swelling is common following revascularization and usually returns to baseline within 2 to 3 months. The etiology is multifactorial, with lymphatic interruption, interstitial edema, and disruption of venous drainage all contributing. Limb swelling tends to worsen with repeat revascularization.

 

Wound Infection

 

Because the most common inflow vessel for distal bypass is the CFA, groin infection is common and occurs in 7% of cases. When an autogenous conduit such as a saphenous vein is used, most infection can be managed with local wound care because it involves the subcutaneous tissue or skin rather than infection of the actual vein. When a prosthetic graft has been used, management of graft infection is a major undertaking. Infection of a LE prosthetic bypass graft is associated with a significant amputation rate because of the tendency for graft thrombosis and anastomotic disruption. Prosthetic graft infections cannot be eradicated with antibiotics, and they mandate graft excision and complex revascularization using a vein, if available.

 

Choice of Conduit for Infrainguinal Bypass Grafting

 

Autogenous Vein

 

Autogenous vein is superior to prosthetic conduits for all infrainguinal bypasses, even in the AK position. This preference is applicable not only for the initial bypass but also for reoperative cases. For long bypasses, ipsilateral great saphenous vein (GSV), contralateral GSV, small saphenous vein, arm vein, and spliced vein are used, in decreasing order of preference. If only a short segment of vein is missing, the SFA can be endarterectomized and the proximal anastomosis performed distally to decrease the length of the conduit and to avoid harvesting and splicing additional vein. When GSV is not available and a relatively short bypass is necessary, arm vein or small saphenous vein is effective. Small saphenous vein is of particular use when a posterior approach is used. If a longer bypass with vein is necessary, arm vein is preferable because it is less awkward to harvest. Another conduit alternative is to harvest the upper arm basilic, median cubital, and cephalic veins in continuity, while incising valves in the basilic segment and using the cephalic segment in reversed configuration to provide a relatively long, unspliced autogenous conduit.

 

Cryopreserved Grafts

 

Cryopreserved grafts are usually cadaveric arteries or veins that have been subjected to rate-controlled freezing with dimethyl sulfoxide and other cryopreservants. Cryopreserved vein grafts are more expensive than prosthetic grafts and are more prone to failure. The endothelial lining is lost as part of the freezing process, making these grafts prone to early thrombosis. Cryopreserved grafts also are prone to aneurysmal degeneration. Despite the fact that these grafts have not performed as well as prosthetic bypasses and autogenous vein in clinical practice, they can still play a role when revascularization is required following removal of infected prosthetic bypass grafts, especially when autogenous vein is unavailable to create a new bypass through clean tissue planes.

 

 

Human Umbilical Vein

 

Human umbilical vein (HUV) is less commonly used than PTFE, because it is thicker and more cumbersome to handle and because of concerns about aneurysmal degeneration. HUV allografts are stabilized with glutaraldehyde and do not have viable cells or antigenic reactivity. These grafts have poor handling characteristics and require extra care when suturing because of an outer Dacron mesh wrapping, which is used to decrease aneurysmal degeneration. Dardik and colleagues have reported favorable results after using HUV and an adjunctive distal arteriovenous fistula. One trial comparing HUV with PTFE and saphenous vein showed that HUV was better than PTFE but worse than saphenous vein in terms of 5-year patency in the AK location. In a systematic review, HUV appears to perform better than cryopreserved veins.

 

Prosthetic Conduits and Adjunctive Modifications

 

If vein is truly unavailable, PTFE or Dacron is the best option for AK bypass. The addition of rings to PTFE did not confer benefit in a single prospective, randomized clinical trial. For infrageniculate prosthetic bypasses, use of a vein patch, cuff, or other venous anastomotic modification can improve patency (52% patency at 2 years for PTFE with vein cuff vs. 29% for PTFE with no cuff) and also improve limb salvage (84% vs. 62%).

Although prosthetic grafts are readily available, easy to handle, and do not require extensive dissection to harvest, their propensity to undergo thrombosis and develop neointimal hyperplasia makes them a less favorable alternative when compared to vein. In a recent review of vein and prosthetic AK femoropopliteal bypasses, the 5-year primary patency rates were reported to be 74 and 39%, respectively. Outcomes were even worse for BK prosthetic bypasses. Unfortunately, the use of autologous venous conduits is not possible in as many as 30% of patients. The GSV may be unsuitable because of small size and poor quality or unavailable due to prior harvest.

Methods to improve prosthetic graft performance have consisted of altering the geometry at the distal anastomosis to get the benefit obtained with vein cuffs (Distaflo, Bard Peripheral Vascular, Tempe, Ariz) and covalently bonding agents onto the luminal surface with anticoagulant, anti-inflammatory and antiproliferative characteristics (Propaten, Gore, Flagstaff, Ariz). One randomized trial that compared precuffed PTFE and PTFE with a vein cuff enrolled 104 patients at 10 centers. Eighty-nine patients were randomized to 47 precuffed PTFE bypasses and 44 bypasses with a vein cuff. At 1 and 2 years, primary patency rates were 52 and 49% for the precuffed group and 62 and 44% for the vein cuffed group, respectively. At 1 year and 2 years, the limb salvage rate was 72 and 65% for the precuffed group and 75 and 62% in the vein cuffed group, respectively. Although numbers are small and follow-up short, the midterm analysis revealed that Distaflo precuffed grafts and PTFE grafts with vein cuff had similar results. The authors concluded that a precuffed graft was a reasonable alternative for infragenicular reconstruction in the absence of saphenous vein. Other authors have been less optimistic and question if there is any benefit derived from geometrically altering prosthetic conduits.

Another approach for improving outcomes when using prosthetic for bypass grafts involves bonding anticoagulants to the conduit. The Gore Propaten graft has heparin bonded onto the luminal surface of the PTFE graft using Carmeda BioActive Surface technology, which immobilizes the heparin molecule with a single covalent bond that does not alter its anticoagulant properties. The heparin binding does not alter the microstructure and handling characteristics of the PTFE. A prospective, randomized trial by Devine and associates suggested that heparin-bonded Dacron or PTFE was superior to plain PTFE for AK popliteal bypasses. The 3-year primary patency for the heparin-bonded grafts was 55% compared with 42% for PTFE (P <.044). Both of these patency rates are inferior to GSV; however, if the improved results with heparin bonding continue to be substantiated, then heparin-bonded prosthetic grafts will become the preferred conduit for AK bypass in the absence of suitable vein. A recent review of available studies with this graft showed an 80% 1-year patency for BK bypasses.195 Randomized, controlled clinical trials with more patients and longer follow-up are necessary to validate whether the PROPATEN vascular graft is superior to other prosthetics, and if, indeed, it is comparable to autogenous vein for BK interventions.

 

Clinical Results of Surgical and Endovascular Interventions for Femoropopliteal Occlusive Disease

 

Balloon angioplasty of the femoropopliteal vessels has not enjoyed the degree of success seen with iliac angioplasty. Patency in this region is dependent upon whether the patient presents with claudication vs. limb-threatening ischemia, the status of the distal runoff vessels, and lesion morphology. Initial technical success for femoropopliteal angioplasty is seen in 80 to 90% of cases, with failures to cross a lesion occurring in 7% of stenoses and 18% of occlusive lesions. Studies have shown that PTA of the femoropopliteal segment achieved greater than a 90% technical success rate and had a 59% primary patency rate at 5-years. PTA of lesions longer than 7 to 10 cm results in compromised patency, while PTA of shorter lesions (<3 cm) gives fairly good results. Lofberg and associates performed 127 femoropopliteal PTA procedures and reported a primary patency rate at 5-year follow-up of 12% in limbs with occlusion longer than 5 cm vs. 32% in limbs with occlusion <5 cm in length. Occlusive lesions have much worse initial technical success rates than stenotic lesions. Concentric lesions respond better to PTA than eccentric lesions, and heavy calcifications have a negative impact on success rates. Distal runoff is another powerful predictor of long-term success.

Johnston and associates analyzed 254 consecutive patients who underwent femoropopliteal PTA and reported a 5-year patency rate of 53% for stenotic lesions and 36% for occlusive lesions in patients with good runoff vs. 5-year patency of 31% for stenotic lesions and 16% for occlusive lesions in patients with poor runoff. A meta-analysis by Hunink and colleagues showed that adjusted 5-year primary patencies after angioplasty of femoropopliteal lesions varied from 12 to 68%, the best results occurring in patients with claudication and stenotic lesions. Although the initial technical success is better for stenoses than occlusions, long-term patency rates for stenoses and short occlusions have been variable and there have been conflicting results regarding the efficacy of stent use. Early published series that examined efficacy of femoropopliteal artery stents showed patency rates that were comparable to stand-alone PTA with primary patency rates varying from 18 to 72% at 3 years. Patient selection and the anatomic character of the lesions may play important roles in the outcomes. Additionally, stent characteristics may contribute to the patency rate. Several clinical studies have demonstrated significant improvements in patency when the newer generations of nitinol stents are used to treat SFA lesions.

Mewissen treated 137 lower limbs in 122 patients with CLI, secondary to TASC II A (n = 12) or TASC II B or C (n = 125) lesions in the SFA. Patients were treated with Cordis SMART self-expanding nitinol stents. Binary restenosis (>50%) was measured by standard duplex velocity criteria at various postintervention intervals. Primary stent patency, defined as absence of binary restenosis in this study, was calculated by life table methods from the time of intervention. The mean lesion length was 12.2 cm (range, 4 to 28 cm). The technical success was 98%. Mean follow-up was 302 days. The primary stent patency rates were 92%, 76%, 66%, and 60% at 6, 12, 18, and 24-months, respectively. Fereira and associates treated 59 patients who had 74 femoropopliteal lesions (60% TASC II D) with Zilver nitinol self-expanding stents (COOK, Bloomington, Ind). Mean recanalization length was 19 cm (range 3 to 53 cm). Mean follow-up time was 2.4 years (range 3 days to 4.8 years). Kaplan-Meier estimates for primary patency rates were 90%, 78%, 74%, 69%, and 69% at 1, 2, 3, 4, and 4.8 years, respectively.

There is general agreement that for suboptimal PTA of an SFA lesion, stent placement is indicated, but a recent randomized trial by Schillinger and associates suggests that primary stenting results in lower restenosis rates than PTA and selective stenting. Restenosis rates at 2 years were 45.7% vs. 69.2% in favor of primary stenting compared with PTA and optional secondary stenting using an intention-to-treat analysis (P = .031). Consistently, stenting, both primary and selective, was superior to stand-alone PTA with respect to the occurrence of restenosis (49.2% vs. 74.3%; P = .028) by a treatment-received analysis.

Nitinol bare metal stents that are designed specifically for BK interventions are showing very encouraging results. Bosiers and colleagues reported their 12-month results using the commercially available non–drug-eluting Xpert (Abbott Vascular, Santa Clara, Calif) nitinol stent system in BK arterial interventions. They had a 12-month primary patency rate of 76.3%, and a limb salvage rate of 95.9%. They followed patients to 12 months and performed angiography with quantitative vessel analysis on the 73% of patients available. Angiography revealed a binary restenosis rate (>50%) of only 20.5%, which is comparable to well-accepted coronary DES study outcomes. The authors attributed this optimal performance to the maintenance of flow dynamics because the stent was specifically designed for use in small vessels. Kickuth and colleagues also have obtained good results using the Xpert stent. After stent placement, the primary cumulative patency rate at 6 months for the study group of 35 patients was 82%. The sustained clinical improvement rate as evidenced by improved ABI was 80%, and freedom from major amputation was 100% at the 6-month follow-up. The rate of major complications was 17%.

Wolf and associates published a multicenter, prospective randomized trial comparing PTA with bypass in 263 men who had iliac, femoral, or popliteal artery obstruction. In 56 patients, cumulative 1-year primary patency after PTA was 43% and, after bypass surgery, was 82%, demonstrating that for long SFA stenoses or occlusions, surgery is better than PTA. Another recent randomized study (BASIL trial) of 452 patients with CLI demonstrated no difference in amputation-free survival at 6 months between surgery and PTA/stenting. The authors commented that surgery was somewhat more expensive and recommended that endovascular intervention should be used as first-line therapy, especially in medically unfit patients. They did conclude that at 2-year follow-up, healthy patients without medical comorbidities derived greater benefit from surgery because it was associated with decreased need for reintervention and had a decreased hazard ratio in terms of all-cause mortality. Using the 2000 TASC II definitions and a Markov state transition model decision analysis, Nolan and colleagues showed that PTA/stenting surpasses bypass efficacy for TASC II C lesions if PTA/stenting primary patency is greater than 32% at 5 years, patient age is >80 years, and/or GSV bypass operative mortality is greater than 6%.

 

MESENTERIC ARTERY DISEASE

 

Vascular occlusive disease of the mesenteric vessels is a relatively uncommon but potentially devastating condition that generally presents in patients more than 60 years of age, is three times more frequent in women, and has been recognized as an entity since 1936. The incidence of such a disease is low and represents 2% of the revascularization operations for atheromatous lesions. The most common cause of mesenteric ischemia is atherosclerotic vascular disease. Autopsy studies have demonstrated splanchnic atherosclerosis in 35 to 70% of cases. Other etiologies exist and include FMD, panarteritis nodosa, arteritis, and celiac artery (CA) compression from a median arcuate ligament, but they are unusual and have an incidence of one iine compared to that of atherosclerosis.

Chronic mesenteric ischemia is related to a lack of blood supply in the splanchnic region and is caused by disease in one or more visceral arteries: the celiac trunk, the SMA, and the IMA. Mesenteric ischemia is thought to occur when two of the three visceral vessels are affected with severe stenosis or occlusion; however, in as many as 9% of cases, only a single vessel is involved [superior mesenteric artery (SMA) in 5% and celiac trunk in 4% of cases].73 This disease process may evolve in a chronic fashion, as in the case of progressive luminal obliteration due to atherosclerosis. On the other hand, mesenteric ischemia can occur suddenly, as in the case of thromboembolism. Despite recent progress in perioperative management and better understanding in pathophysiology, mesenteric ischemia is considered one of the most catastrophic vascular disorders, with mortality rates ranging from 50 to 75%. Delay in diagnosis and treatment are the main contributing factors in its high mortality. It is estimated that mesenteric ischemia accounts for one in every 1000 hospital admissions in this country. The prevalence is rising due in part to the increased awareness of this disease, the advanced age of the population, and the significant comorbidity of these elderly patients. Early recognition and prompt treatment before the onset of irreversible intestinal ischemia are essential to improve the outcome.

 

Anatomy and Pathophysiology

 

Mesenteric arterial circulation is remarkable for its rich collateral network. Three main mesenteric arteries provide the arterial perfusion to the GI system: the CA, SMA, and IMA. In general, the CA provides arterial circulation to the foregut (distal esophagus to duodenum), hepatobiliary system, and spleen; the SMA supplies the midgut (jejunum to midcolon); and the IMA supplies the hindgut (midcolon to rectum). The CA and SMA arise from the ventral surface of the infradiaphragmatic suprarenal abdominal aorta, while the IMA originates from the left lateral portion of the infrarenal aorta. These anatomic origins in relation to the aorta are important when a mesenteric angiogram is performed to determine the luminal patency. To fully visualize the origins of the CA and SMA, it is necessary to perform both an anteroposterior and a lateral projection of the aorta because most arterial occlusive lesions occur in the proximal segments of these mesenteric trunks.

Because of the abundant collateral flow between these mesenteric arteries, progressive diminution of flow in one or even two of the main mesenteric trunks is usually tolerated, provided that uninvolved mesenteric branches can enlarge over time to provide sufficient compensatory collateral flow. In contrast, acute occlusion of a main mesenteric trunk may result in profound ischemia due to lack of sufficient collateral flow. Collateral network between the CA and the SMA exist primarily through the superior and inferior pancreaticoduodenal arteries. The IMA may provide collateral arterial flow to the SMA through the marginal artery of Drummond, the arc of Riolan, and other unnamed retroperitoneal collateral vessels termed meandering mesenteric arteries (Fig. 25). Lastly, collateral visceral vessels may provide important arterial flow to the IMA and the hindgut through the hypogastric arteries and the hemorrhoidal arterial network.

 

 

Fig. 25. An aortogram showing a prominent collateral vessel that is the arc of Riolan (arrow) in a patient with an inferior mesenteric artery occlusion. This vessel network provides collateral flow between the superior mesenteric artery and inferior mesenteric artery

 

Regulation of mesenteric blood flow is largely modulated by both hormonal and neural stimuli, which characteristically regulate systemic blood flow. In addition, the mesenteric circulation responds to the GI contents. Hormonal regulation is mediated by splanchnic vasodilators such as nitric oxide, glucagon, and vasoactive intestinal peptide. Certain intrinsic vasoconstrictors such as vasopressin can diminish the mesenteric blood flow. On the other hand, neural regulation is provided by the extensive visceral autonomic innervation.

Clinical manifestation of mesenteric ischemia is predominantly postprandial abdominal pain, which signifies that the increased oxygen demand of digestion is not met by the GI collateral circulation. The postprandial pain frequently occurs in the midabdomen, suggesting that the diversion of blood flow from the SMA to supply the stomach impairs perfusion to the small bowel. This leads to transient anaerobic metabolism and acidosis. Persistent or profound mesenteric ischemia will lead to mucosal compromise with release of intracellular contents and by-products of anaerobic metabolism to the splanchnic and systemic circulation. Injured bowel mucosa allows unimpeded influx of toxic substances from the bowel lumen with systemic consequences. If full-thickness necrosis occurs in the bowel wall, intestinal perforation ensues, which will lead to peritonitis. Concomitant atherosclerotic disease in cardiac or systemic circulation frequently compounds the diagnostic and therapeutic complexity of mesenteric ischemia.

 

Types of Mesenteric Artery Occlusive Disease

 

There are three major mechanisms of visceral ischemia involving the mesenteric arteries, which include: (a) acute mesenteric ischemia, which can be either embolic or thrombotic in origin; (b) chronic mesenteric ischemia; and (c) nonocclusive mesenteric ischemia. Despite the variability of these syndromes, a common anatomic pathology is involved in these processes. The SMA is the most commonly involved vessel in acute mesenteric ischemia. Acute thrombosis occurs in patients with underlying mesenteric atherosclerosis, which typically involves the origin of the mesenteric arteries while sparing the collateral branches. In acute embolic mesenteric ischemia, the emboli typically originate from a cardiac source and frequently occur in patients with atrial fibrillation or following myocardial infarction (Figs. 26 and 27). Nonocclusive mesenteric ischemia is characterized by a low flow state in otherwise normal mesenteric arteries, and most frequently occurs in critically ill patients on vasopressors. Finally, chronic mesenteric ischemia is a functional consequence of a long-standing atherosclerotic process that typically involves at least two of the three main mesenteric vessels. The gradual development of the occlusive process allows the development of collateral vessels that prevent the manifestations of acute ischemia, but are not sufficient to meet the high postprandial intestinal oxygen requirements, giving rise to the classical symptoms of postprandial abdominal pain and the resultant food fear.

 

 

Fig.26. An anteroposterior view of a selective superior mesenteric artery angiogram showed an abrupt cutoff of the middle colic artery, which was caused by emboli (arrow) due to atrial fibrillation

 

Fig. 27. A lateral mesenteric angiogram showing an abrupt cutoff of the proximal superior mesenteric artery, which is consistent with superior mesenteric artery embolism (arrow).

 

Mesenteric arteriography also can play a therapeutic role. Once the diagnosis of nonocclusive mesenteric ischemia is made on the arteriogram, an infusion catheter can be placed at the SMA orifice and vasodilating agents such as papaverine can be administered intra-arterially. The papaverine infusion may be continued postoperatively to treat persistent vasospasm, a common occurrence following mesenteric reperfusion. Transcatheter thrombolytic therapy has little role in the management of thrombotic mesenteric occlusion. Although thrombolytic agents may transiently recannulate the occluded vessels, the underlying occlusive lesions require definitive treatment. Furthermore, thrombolytic therapy typically requires a prolonged period of time to restore perfusion, during which the intestinal viability will be difficult to assess.

A word of caution would be appropriate here regarding patients with typical history of chronic intestinal angina who present with an acute abdomen and classical findings of peritoneal irritation. Arteriography is the gold standard for the diagnosis of mesenteric occlusive disease; however, it can be a time-consuming diagnostic modality. In this group of patients, immediate exploration for assessment of intestinal viability and vascular reconstruction is the best choice.

 

Surgical Repair

 

Acute Embolic Mesenteric Ischemia

 

Initial management of patients with acute mesenteric ischemia includes fluid resuscitation and systemic anticoagulation with heparin to prevent further thrombus propagation. Significant metabolic acidosis not responding to fluid resuscitation should be corrected with sodium bicarbonate. A central venous catheter, peripheral arterial catheter, and a Foley catheter should be placed for hemodynamic status monitoring. Appropriate antibiotics are given before surgical exploration. The operative management of acute mesenteric ischemia is dictated by the cause of the occlusion. It is helpful to obtain a preoperative mesenteric arteriogram to confirm the diagnosis and to plan appropriate treatment options. However, the diagnosis of mesenteric ischemia frequently cannot be established before surgical exploration; and therefore, patients in a moribund condition with acute abdominal symptoms should undergo immediate surgical exploration, avoiding the delay required to perform an arteriogram.

The primary goal of surgical treatment in embolic mesenteric ischemia is to restore arterial perfusion with removal of the embolus from the vessel. The abdomen is explored through a midline incision, which often reveals variable degrees of intestinal ischemia from the midjejunum to the ascending or transverse colon. The transverse colon is lifted superiorly, and the small intestine is reflected toward the right upper quadrant. The SMA is approached at the root of the small bowel mesentery, usually as it emerges from beneath the pancreas to cross over the junction of the third and fourth portions of the duodenum. Alternatively, the SMA can be approached by incising the retroperitoneum lateral to the fourth portion of the duodenum, which is rotated medially to expose the SMA. Once the proximal SMA is identified and controlled with vascular clamps, a transverse arteriotomy is made to extract the embolus, using standard balloon embolectomy catheters. In the event the embolus has lodged more distally, exposure of the distal SMA may be obtained in the root of the small bowel mesentery by isolating individual jejunal and ileal branches to allow a more comprehensive thromboembolectomy. Following the restoration of SMA flow, an assessment of intestinal viability must be made, and nonviable bowel must be resected. Several methods have been described to evaluate the viability of the intestine, which include intraoperative IV fluorescein injection and inspection with a Wood’s lamp, and Doppler assessment of antimesenteric intestinal arterial pulsations. A second-look procedure should be considered in many patients, and is performed 24 to 48 hours following embolectomy. The goal of the procedure is reassessment of the extent of bowel viability, which may not be obvious immediately following the initial embolectomy. If nonviable intestine is evident in the second-look procedure, additional bowel resections should be performed at that time.

 

Acute Thrombotic Mesenteric Ischemia

 

Thrombotic mesenteric ischemia usually involves a severely atherosclerotic vessel, typically the proximal CA and SMA. Therefore, these patients require a reconstructive procedure to the SMA to bypass the proximal occlusive lesion and restore adequate mesenteric flow. The saphenous vein is the graft material of choice, and prosthetic materials should be avoided in patients with nonviable bowel, due to the risk of bacterial contamination if resection of necrotic intestine is performed. The bypass graft may originate from either the aorta or iliac artery. Advantages from using the supraceliac infradiaphragmatic aorta as opposed to the infrarenal aorta as the inflow vessel include a more smooth graft configuration with less chance of kinking, and the absence of atherosclerotic disease in the supraceliac aortic segment. Exposure of the supraceliac aorta is technically more challenging and time consuming than that of the iliac artery, which, unless calcified, is an appropriate inflow. Patency rates are similar regardless of inflow vessel choice.

 

Chronic Mesenteric Ischemia

 

The therapeutic goal in patients with chronic mesenteric ischemia is to revascularize mesenteric circulation and prevent the development of bowel infarction. Mesenteric occlusive disease can be treated successfully by either transaortic endarterectomy or mesenteric artery bypass. Transaortic endarterectomy is indicated for ostial lesions of patent CA and SMA. A left medial rotation is performed, and the aorta and the mesenteric branches are exposed. A lateral aortotomy is performed, encompassing both the CA and SMA orifices. The visceral arteries must be adequately mobilized so that the termination site of endarterectomy can be visualized. Otherwise, an intimal flap may develop, which can lead to early thrombosis or distal embolization.

For occlusive lesions located 1 to 2 cm distal to the mesenteric origin, mesenteric artery bypass should be performed. Multiple mesenteric arteries are typically involved in chronic mesenteric ischemia, and both the CA and SMA should be revascularized whenever possible. In general, bypass grafting may be performed either antegrade from the supraceliac aorta or retrograde from either the infrarenal aorta or iliac artery. Both autogenous saphenous vein grafts and prosthetic grafts have been used with satisfactory and equivalent success. An antegrade bypass also can be performed using a small-caliber bifurcated graft from the supraceliac aorta to both the CA and SMA, which yields an excellent long-term result.

 

Celiac Artery Compression Syndrome

 

The decision to intervene in patients with CA compression syndrome should be based on both an appropriate symptom complex and the finding of CA compression in the absence of other findings to explain the symptoms. The treatment goal is to release the ligamentous structure that compresses the proximal CA and to correct any persistent stricture by bypass grafting. The patient should be cautioned that relief of the celiac compression cannot be guaranteed to relieve the symptoms. In a number of reports on endovascular management of chronic mesenteric ischemia, the presence of CA compression syndrome has been identified as a major factor of technical failure and recurrence. Therefore, angioplasty and stenting should not be undertaken if extrinsic compression of the CA by the median arcuate ligament is suspected based on preoperative imaging studies. Open surgical treatment should be performed instead.

 

Endovascular Treatment

 

Chronic Mesenteric Ischemia

 

Endovascular treatment of mesenteric artery stenosis or short segment occlusion by balloon dilatation or stent placement represents a less invasive therapeutic alternative to open surgical intervention, particularly in patients whose medical comorbidities place them in a high operative risk category. Endovascular therapy is also suited to patients with recurrent disease or anastomotic stenosis following previous open mesenteric revascularization. Prophylactic mesenteric revascularization is rarely performed in the asymptomatic patient undergoing an aortic procedure for other indications. However, the natural history of untreated chronic mesenteric ischemia may justify revascularization in some minimally symptomatic or asymptomatic patients if the operative risks are acceptable, because the first clinical presentation may be acute intestinal ischemia in as many as 50% of the patients, with a mortality rate that ranges from 15 to 70%. This is particularly true when the SMA is involved. Mesenteric angioplasty and stenting is particularly suitable for this patient subgroup given its low morbidity and mortality. Because of the limited experience with stent use in mesenteric vessels, appropriate indications for primary stent placement have not been clearly defined. Guidelines generally include calcified ostial stenoses, high-grade eccentric stenoses, chronic occlusions, and significant residual stenosis greater than 30% or the presence of dissection after angioplasty. Restenosis after PTA is also an indication for stent placement.

 

Acute Mesenteric Ischemia

 

Catheter-directed thrombolytic therapy is a potentially useful treatment modality for acute mesenteric ischemia, which can be initiated with intra-arterial delivery of thrombolytic agent into the mesenteric thrombus at the time of diagnostic angiography. Various thrombolytic medications, including urokinase (Abbokinase, Abbott Laboratory, North Chicago, Ill) or recombinant tissue plasminogen activator (Activase, Genentech, South San Francisco, Calif), have been reported to be successful in a small series of case reports. Catheter-directed thrombolytic therapy has a higher probability of restoring mesenteric blood flow success when performed within 12 hours of symptom onset. Successful resolution of a mesenteric thrombus will facilitate the identification of the underlying mesenteric occlusive disease process. As a result, subsequent operative mesenteric revascularization or mesenteric balloon angioplasty and stenting may be performed electively to correct the mesenteric stenosis. There are two main drawbacks with regard to thrombolytic therapy in mesenteric ischemia. Percutaneous, catheter-directed thrombolysis (CDT) does not allow the possibility to inspect the potentially ischemic intestine following restoration of the mesenteric flow. Additionally, a prolonged period of time may be necessary to achieve successful CDT, due in part to serial angiographic surveillance to document thrombus resolution. An incomplete or unsuccessful thrombolysis may lead to delayed operative revascularization, which may further necessitate bowel resection for irreversible intestinal necrosis. Therefore, catheter-directed thrombolytic therapy for acute mesenteric ischemia should only be considered in selected patients under a closely scrutinized clinical protocol.

 

Nonocclusive Mesenteric Ischemia

 

The treatment of nonocclusive mesenteric ischemia is primarily pharmacologic with selective mesenteric arterial catheterization followed by infusion of vasodilatory agents such as tolazoline or papaverine. Once the diagnosis is made on the mesenteric arteriography, intra-arterial papaverine is given at a dose of 30 to 60 mg/h. This must be coupled with the cessation of other vasoconstricting agents. Concomitant IV heparin should be administered to prevent thrombosis in the cannulated vessels. Treatment strategy thereafter is dependent on the patient’s clinical response to the vasodilator therapy. If abdominal symptoms improve, mesenteric arteriography should be repeated to document the resolution of vasospasm. The patient’s hemodynamic status must be carefully monitored during papaverine infusion, as significant hypotension can develop in the event that the infusion catheter migrates into the aorta, which can lead to systemic circulation of papaverine. Surgical exploration is indicated if the patient develops signs of continued bowel ischemia or infarction as evidenced by rebound tenderness or involuntary guarding. In these circumstances, papaverine infusion should be continued intraoperatively and postoperatively. The OR should be kept as warm as possible, and warm irrigation fluid and laparotomy pads should be used to prevent further intestinal vasoconstriction during exploration.

 

Techniques of Endovascular Interventions

 

To perform endovascular mesenteric revascularization, intraluminal access is performed via a femoral or brachial artery approach. Once an introducer sheath is placed in the femoral artery, an anteroposterior and lateral aortogram just below the level of the diaphragm is obtained with a pigtail catheter to identify the origin of the CA and SMA. Initial catheterization of the mesenteric artery can be performed using a variety of selective angled catheters, which include the RDC, Cobra-2, Simmons I (Boston Scientific/Meditech, Natick, Mass), or SOS Omni catheter (AngioDynamics, Queensbury, NY). Once the mesenteric artery is cannulated, systemic heparin (5000 IU) is administered IV. A selective mesenteric angiogram is then performed to identify the diseased segment, which is followed by the placement of a 0.035-in or less traumatic 0.014- to 0.018-in guidewire to cross the stenotic lesion. Once the guidewire is placed across the stenosis, the catheter is carefully advanced over the guidewire across the lesion. In the event that the mesenteric artery is severely angulated as it arises from the aorta, a second stiffer guidewire (Amplatz or Rosen Guidewire, Boston Scientific) may be exchanged through the catheter to facilitate the placement of a 6F guiding sheath (Pinnacle, Boston Scientific).

With the image intensifier angled in a lateral position to fully visualize the proximal mesenteric segment, a balloon angioplasty is advanced over the guidewire through the guiding sheath and positioned across the stenosis. The balloon diameter should be chosen based on the vessel size of the adjacent normal mesenteric vessel. Once balloon angioplasty is completed, a postangioplasty angiogram is necessary to document the procedural result. Radiographic evidence of either residual stenosis or mesenteric artery dissection constitutes suboptimal angioplasty results that warrant mesenteric stent placement. Moreover, atherosclerotic involvement of the proximal mesenteric artery or vessel orifice should be treated with a balloon-expandable stent placement. These stents can be placed over a low profile 0.014- or 0.018-in guidewire system. It is preferable to deliver the balloon-mounted stent through a guiding sheath, which is positioned just proximal to the mesenteric orifice while the balloon-mounted stent is advanced across the stenosis. The stent is next deployed by expanding the angioplasty balloon to its designated inflation pressure. The balloon is then deflated and carefully withdrawn through the guiding sheath.

Completion angiogram is performed by hand injecting a small volume of contrast though the guiding sheath. It is critical to maintain the guidewire access until a satisfactory completion angiogram is obtained. If the completion angiogram reveals suboptimal radiographic results, such as residual stenosis or dissection, additional catheter-based intervention can be performed through the same guidewire. These interventions may include repeat balloon angioplasty for residual stenosis or additional stent placement for mesenteric artery dissection. During the procedure, intra-arterial infusion of papaverine or nitroglycerine can be used to decrease vasospasm. Administration of antiplatelet agents is also recommended, for at least 6 months or even indefinitely if other risk factors of cardiovascular disease are present.

 

Complications of Endovascular Treatment

 

Complications are not common and rarely become life threatening. These include access site thrombosis, hematomas, and infection. Dissection can occur during PTA and is managed with placement of a stent. Balloon-mounted stents are preferred over the self-expanding ones because of the higher radial force and the more precise placement. Distal embolization has also been reported but it never resulted in acute intestinal ischemia, likely due to the rich network of collaterals already developed.

Leave a Reply

Your email address will not be published. Required fields are marked *

Приєднуйся до нас!
Підписатись на новини:
Наші соц мережі