LECTURE 4
OPERATIVE SURGERY OF ORGANS OF MEDIASTIUM AND HEART
Pericardium
PERICARDIAL SAC The pericardium is a fibroserous sac which is located in the middle mediastinum and encloses the heart and the roots of the great vessels. It has the appearance of a truncated cone with its base resting on and fused with the central portion of the diaphragm. Its blunt apex reaches the level of the second costal cartilage. The outlineof the pericardium corresponds to that of the heart except that it reaches the 2nd costal cartilage on both sides, whereas the heart extends only to the 3rd cartilage on the righ.
PERICARDIAL LAYERS The pericardium has 3 layers so arranged that the fibrous pericardium is entirely parietal, but the serous has both visceral and parietal layers.
FIBROUS PERICARDIUM
The fibrous pericardium is applied to and is firmly fused with the outer surface of the parietal layer of serous pericardium. It is a sheet of considerable strength which fuses with the central tendon of the diaphragm interiorly and can be separated from it only by sharp dissection. Superiorly and posteriorly, it blends with the outer coats of the great vessels as they enter or leave the pericardial sac. It is by means of the outer fibrous coat of the arch of the aorta that the fibrous pericardium blends with the pretracheal layer of deep cervical fascia.
Relations. The fibrous pericardium lies behind the body of the sternum and the costal cartilages from the 2nd to the 6th inclusive. Its anterior surface is separated from these structures-by the lungs and the pleura except at 2 places. One point of contact is in the median plane, where the fibrous sac is attached to the upper and the lower parts of the body of the sternum. This is brought about by two condensations of mediastinal areolar tissue which are called the upper and the lower sternopericardial ligaments; these are of clinical importance in adhesive pericarditis. The other point of contact is in the region of the bare area of the pericardium, which has no covering of lung. This is located at the sternal end of the left 5th costal cartilage. Here the cardiac notch leaves a deficient area of left pleura, and the pericardium comes in direct relation to the left sternocostalismuscle and the sternum. This area is of importance to the surgeon, since he may tap the pericardial sac at this point without injury to the pleura. Both side walls of the pericardium are in relation to the mediastinal pleura.
VISCERAL AND PARIETAL LAYERS The visceral layer of serous pericardium is usually called the epicardium. It is exceedingly thin and is so closely adherent to the outer surface of the heart that any attempt to detach it results in injury to the superficial layers of cardiac musculature. The visceral layer covers the anterior and inferior surfaces of the heart and ascends on the back of the left atrium, where it is reflected downward as the parietal layer of serous pericardium. The parietal layer follows and adheres to the fibrous pericardium. The pericardial sac can be marked on the surface of the thorax as extending from the 2nd costal cartilage above to the 6th below. On the right, it extends for Vi inch beyond the right margin of the sternum, and to the left it forms a line which passes upward and medial from the cardiac apex to the 2nd left costal cartilage about 1 1/2 inches from the midline. The latter is convex upward and to the left. The parietal and the visceral layers of pericardium are continuous with each other anteriorly where the great arteries leave the heart, and posteriorly where the great veins enter it. That space which exists between the 2 layers of serous pericardium is a potential cavity called the pericardial cavity. It contains sufficient serous fluid to minimize friction between its 2 surfaces during heart action.
SURGICAL CONSIDERATIONS PERICARDIOCENTESIS
Aspiration of the pericardial cavity is done for diagnostic purposes or to release pressure in the pericardial cavity. Even with large effusions, the heart remains anterior and may be injured during this procedure. The aspirating needle should be placed to the left of the xiphoid, thus avoiding the internal mammary artery. Then it should be directed upward, backward and to the left, so that the heart is avoided and the left lateral pouch of dilated pericardium entered. If the needle is passed straight back, the left coronary artery may be injured.
PERICARDIOSTOMY (PERTCARDIOTOMY)
C. S. Beck and others have emphasized the importance of the subatmospheric pressure which exists in the mediastinum. When the pericardium is opened, this is raised to atmospheric pressure, and the resultant compression on the heart causes a rise in venous pressure and a slight transient fall in arterial pressure. A normal heart may tolerate these changes, but should the heart be damaged, the patient might succumb. Many incisions and approaches for the purposes of draining the pericardial cavity have been described. One of the more common extends from the junction of the left 5th costal cartilage and sternum downward over the cartilages of the 5th, the 6th and the 7th ribs. About an inch of cartilage of the 5th, the 6th and the 7th ribs is removed, and the internal mammary vessels are ligated. The pericardium lies beneath, and the pleural space is to the left. An incision is made into the pericardium, and the fluid is aspirated from each lateral pericardial recess and from the oblique sinus. The pericardium is left open to drain. Soft rubber tubes are introduced into the opening; however, this is to be avoided in tuberculous pericarditis.
Heart
THE HEART PROPER With the pericardium opened, the heart presents a fixed posterosuperior portion—the atria (auricles); and a free antero-inferior portion—the ventricles. A groove containing fat, the auriculoventricular groove (coronary sulcus), marks the line of separation between atria and ventricles; it contains the right coronary artery. Passing downward and to the left, a similar groove is found which divides the ventricular portion of the heart, as seen in front, into a larger right and a smaller left ventricle. This groove corresponds to the attachments of the anterior margin of the septum between the right and the left ventricles and is known as the anterior interventricular groove (anterior longitudinal sulcus); it contains the anterior descending branch of the left coronary artery. The right border of the heart is formed by the right atrium; the left border is formed, almost entirely, by the left ventricle. The auricle of the left atrium aids in the formation of the left border at its uppermost part. Between the 2 auricles, the lower part of the pulmonary trunk covers the ascending aorta. That part of the right ventricle which is immediately below the pulmonary trunk is called the infundibulum. If the left index finger is passed in front of the superior vena cava, it can be directed from right to left behind the aorta and the pulmonary artery. The finger now lies in the transverse sinus of the pericardium. If the thumb is brought into contact with this index finger, the arterial end (aorta and pulmonary artery) of the heart lies between the 2 digits. All large vessels below the transverse pericardial sinus constitute veins (superior and inferior venae cavae and pulmonary veins). The sinus is bounded in front by the aorta and the pulmonary artery, and behind by the superior vena cava and the left atrium. The transverse sinus connects the right and the left upper portions of the pericardial cavity. It is through this sinus that a rubber catheter is placed in the Trendelenburg operation for pulmonary embolus. If the fingers of the right hand are placed behind the apex of the heart and passed upward and to the right, they are stopped in a cul-de-sac of pericardium which lies behind the heart, between the left atrium and the pericardium. This is known as the oblique sinus of the pericardium. It is really an inverted “U” bounded below and on the right by the inferior vena cava and the right pulmonary veins, and above and on the left by the pulmonary veins. The sinus lies in front of the esophagus and the descending thoracic aorta. Fingers placed in the transverse and the oblique sinuses cannot touch each other because they are separated by 2 layers of serous pericardium surrounding the veins as they enter the left atrium.
COMPARTMENTS OF THE HEART. The compartments of the heart may be studied in the order in which they are traversed by the blood
Right Atrium. The right atrium begins at the orifice of the inferior vena cava behind the 6th right cartilage. Immediately in front of the opening of the superior and the inferior venae cavae, an indistinct line might be seen which is called the sulcus terminalis. This line is of interest because it indicates the junction between the sinus venosus and the right auricle and marks a ridge which is on the inside of the right auricle called the crista terminalis. The sinus venosus is represented in the adult human heart by that part of the right auricle which lies behind the sulcus and receives the superior and the inferior venae cavae. If a window is cut in the right auricle, the crista terminalis is seen extending from the front of the orifice of the superior vena cava to the front of the orifice of the inferior vena cava. The atrium behind the crista is smooth, and in front it is trabeculated. The rugose appearance of the auricle in front of the crista is brought about by muscle bands which resemble the teeth of a comb; hence, the name musculi pectinati. The posterior wall of the atrium epresents the atrial septum, which separates the right atrium in front from the left behind. Near its center is noted a shallow oval depression, which is bounded by a thickened ridge every-where except below. This depression is the fossa ovalis, and the ridge surrounding it is the annulus ovalis (limbus fossae ovalis). From the anterior horn of the annulus, there will usually be seen a crescentric membrane which passes forward and to the right, reaching the anterior wall of the auricle immediately in front of and to the right of the opening of the inferior vena cava. It is called the eustachian valve (valve of the inferior vena cava), which directed blood in the fetus from the inferior vena cava to the fossa ovalis, and was known as the foramen ovale. The tricuspid orifice (right atrioventricular orifice) occupies the lower portion of the anterior wall of the right atrium. It is large enough to admit the tips of 3 fingers; it opens into the lower and posterior part of the right ventricle and is bounded by the tricuspid valve. The surface projection of this aperture lies obliquely behind the sternum close to the midline and extends from the level of the 4th left costal cartilage to the level of the 6th right cartilage. Medial to the opening of the inferior vena cava, the coronary sinus may be found. The opening of the sinus points to the left and is guarded by a small pocketlike valve called the coronary valve (Thebesius), which turns the blood of the coronary sinus forward into the atrioventricular orifice.
Right Ventricle. This chamber has a thick muscle wall and is somewhat triangular in outline. The infundibulum (conus arteriosus) is the uppermost part of the right ventricle, the walls of which are smooth and have no projecting muscular bundles; it leads into the pulmonary artery. The inner surface of the right ventricle is extremely irregular because of a lacework of muscular ridges which are called the trabeculae carnea. A number of conical muscular projections are also found; these are the papillary muscles. They are attached at their bases to the wall of the ventricle, and their apices are connected to the cusps of the tricuspid valve by a number of tendinous strands called the chordae tendinae. The entrance to the right ventricle is by way of the right atrioventricular orifice, and the exit is the pulmonary orifice. The right atrioventricular orifice is situated at the lower and posterior part of the ventricle; it is about
Left Atrium. The left atrium is quadrilateral in shape, and its interior reveals the openings of the 4 pulmonary veins, usually 2 on either side. These veins are unguarded by valves. The interior of the chamber is quite smooth except in its auricular portion, where musculi pectinati are present. Blood leaves the left atrium and enters the left ventricle via the left atrioventricular orifice. This is smaller than the one on the right and admits only 2 fingers
Left Ventricle. The cavity of the left ventricle is longer and narrower than that of the right, and the walls are much thicker. Its interior reveals a dense meshwork of trabeculae carneae which are finer but more numerous than those of the right. However, the papillary muscles of this ventricle are less numerous and much stronger; the chordae tendinae from each papillary muscle pass to both cusps of the mitral valve. The left atrioventricular orifice is surrounded by the bicuspid (mitral) valve, which consists of a larger anterior cusp and a smaller posterior one. Blood leaves the left ventricle via the aortic orifice, which is at the upper right and posterior part, and (like the pulmonary orifice) is surrounded by a fibrous ring to which the bases of the cusps of the aortic valve are attached. The aortic valve, like the pulmonary, has 3 semilunar cusps
BLOOD VESSELS AND NERVES
The trunk of the pulmonary artery arises from the infundibulum of the right ventricle, passes upward and backward and carries the blood from the right ventricle to the lung. It is about
The coronary arteries are the nutrient vessels of the heart. They arise from dilatations of the root of the aorta, which are called the sinuses of the aorta. There are 3 such sinuses—1 anterior and 2 posterior—but only 2 coronary arteries —a right and a left. The right coronary arises from the anterior sinus, and the left from the left posterior sinus. The origins of these vessels are hidden anteriorly by the right auricular appendix and the pulmonary artery. The vessels pass forward, one on by marking 6 points on the anterior chest wall. either side of the pulmonary artery, and have the corresponding auricular appendage to their lateral sides. The right artery travels in the right atrioventricular sulcus to the back of the heart until it reaches the beginning of the posterior interventricular groove, where it gives rise to a well-developed posterior descending interventricular branch. The left coronary artery reaches the anterior interventricular sulcus, into which it sends an anterior descending interventricular branch, and the main trunk of the artery (circumflex artery) continues around the left side of the heart to reach its posterior aspect. The course of this vessel may be obscured by fat in the left auriculoventricular sulcus. The cardiac veins accompany the arteries in the sulci and usually are superficial to the arteries. The companion of the left coronary artery is the great cardiac vein. It follows the course of the interventricular branch of the left coronary artery and the circumflex branch. The companion of the interventricular branch of the right coronary artery is the middle cardiac vein. Most of the venous blood of the heart enters the coronary sinus, which lies in the atrioventricular sulcus at the lower end of the oblique pericardial sinus. It is about 1 1/2 inches long and opens into the right atrium at the left of the orifice of the inferior vena cava. The nerves which supply the heart are derived from the vagus and the cervical ganglionated chain. They spread over the aortic arch and the heart and are distributed with the branches of the coronary vessels
SURGICAL CONSIDERATIONS EXPOSURE OF THE HEART
Many incisions have been described, but only the more popular ones are considered. The Duval-Barasty incision to the pericardium and the heart gives excellent exposure and protects the pleural cavities. Its only drawback is that it takes time to open and close and may be associated with shock. The incision is made in the midline from the 2nd rib to the midepigastrium. The xiphoid is removed, and the sternum is split to the 2nd interspace where it is cut transversely. The split halves of the sternum are retracted, the pleurae pushed aside, and the pericardium opened anteriorly. The diaphragm and the anterior pericardium are incised, making the incision a thoraco-abdominal one. Spangaro’s incision is really an intercostochondral thoracotomy which provides a rapid approach to the heart but not as good exposure as does the Duval-Barasty. The incision is made through the 4th intercostals space from the margin of the sternum to the anterior axillary line. The internal mammary vessels are ligated and divided. The 4th and the 5th ribs and cartilages are separated, and the left lung is retracted. The pericardium is incised in the long axis of the heart, and the pathologic areas are exposed and treated. Parasternal and semicircular incisions which utilize flaps have also been advocated.
WOUNDS OF THE HEART
The immediate dangers in heart wounds are tamponade and hemorrhage. Aspiration while preparations for the operation are being made may be lifesaving. D. C. Elkin has reviewed this subject and emphasizes that, if time permits, all efforts should be made to avoid entering the pleural cavity, since a pneumothorax adds to the shock. One of the above-mentioned incisions is utilized, and the wound in the pericardium is located and enlarged. If this is not found, the pericardium is opened between stay sutures. When the intrapericardial pressure is released, the bleeding becomes profuse, and the contractions of the heart increase in force. The greatest difficulty is encountered in placing the first stitch. When the cardiac wound is located, the index finger of the left hand is placed over it, and the surrounding blood is removed by suction. The first suture is placed directly beneath the finger and may be used for traction and hemostasis. Then the wound is closed with unabsorbable suture material, the sutures passing into the muscle but not into the heart chambers. Claude Beck has emphasized the fact that wounds located in the edges of the heart, on its posterior surface, or behind the sternum are reached best by placing an apex suture. By this method the heart may be rotated so that the injury can be exposed properly. Beck’s control suture steadies the heart while the other sutures are being placed. The pericardium should be closed loosely with interrupted sutures so that space is allowed for drainage of the intrapericardial fluid which will accumulate. Muscle, fascia and skin are closed in layers
CONGENITAL DEFECTS
Congenital defects of the heart and the great vessels were described as early as 1777 by the eminent Dutch physician Sandifort, who gave a remarkably clear description of what is known today as the “tetralogy of Fallot.” One of the most prolific contributors to the knowledge of these anomalies was Maude E. Abbott. To her goes the credit in a large measure for being responsible for today’s diagnostic precision which resulted in a new and gratifying field of surgery. When one discusses these dramatic events, the names of Bailey, Blalock, Crafoord, Gross and Taussig must be mentioned also.
Cor Biloculare (2-Chambered Heart). This is a most primitive type of cardiac defect Tt has a single atrium, a single ventricle and a common atrioventricular valve. It must be remembered that many anomalies may appear in a given specimen. Therefore, in the diagram herein presented it will be noted that the pulmonary artery lies behind the aorta and is atretic. Pulmonary circulation takes place via a patent ductus arteriosus. Death ensues in these patients in infancy or early childhood.
Cor Triloculare Biatriatum (3-Chambered Heart) consists of 2 atria and a single ventricle. No ventricular septum exists, and in the diagram shown here there is an associated transposition of the aorta and the pulmonary artery. It resembles the 2-chambered heart in that there is a free admixture of venous and aerated blood in the single ventricle. The chances of survival are somewhat greater than in the 2-chambered heart, although death occurs commonly during infancy.
The tetralogy of Fallot as originally described consisted of
1. Pulmonary stenosis (atresia)
2. Dextraposition of the aorta
3. Interventricular septal defect
4. Hypertrophy of the right ventricle
This is the most common malformation associated with cyanosis which permits the patients to survive beyond 2 years of age. Potts and Blalock have attempted to correct the pulmonary stenosis by creating an artificial ductus arteriosus. Potts accomplished this by performing a side-to-side anastomosis between the pulmonary artery and the aorta. The Blalock procedure consists of an end-to-side anastomosis between a systemic branch of the aorta (subclavian) and one of the 2 pulmonary arteries. Numerous modifications of these procedures have been described.
The Eisenmenger complex reveals a heart that has a ventricular septal defect with biventricular origin of the aorta. The aorta straddles a defect in the membranous portion of the ventricular septum. Because of this the right and the left ventricles share in the propelling of blood into the aorta; the pressure in the 2 ventricles is similar, being at systemic levels. In the Eisenmenger complex the small arteries in the lungs closely resemble those of the normal fetus in which there is increased resistance to pulmonary blood flow
Patent ductus arteriosus permits blood to flow from the aorta into the pulmonary artery. It should be recalled that during fetal life the ductus arteriosus is a normally functioning channel which short-circuits blood from the pulmonary artery to the aorta. This should become obliterated at or shortly after birth. If the ductus remains open, great volumes of blood reach the pulmonary artery via the aorta and are reflected in a left ventricular dilatation and hypertrophy. Two types of patent ductus arteriosus have been described: one in which it is cylindrical and one in which it is stubby, the latter being known as the window type. Evidence of progressive cardiac failure in an acyanotic infant strongly suggests the possibility of this condition. The patient frequently lives to adult life; however, life expectancy is reduced materially. Among the chief causes of death in untreated cases are bacterial infection and left ventricular failure. The closure of a patent ductus arteriosus is now a standard surgical procedure.
Mediastinum
The mediastinum is the middle compartment of the chest which is situated between the 2 pleural cavities. Its boundaries are: anterior, the sternum; posterior the bodies of the 12 thoracic vertebrae; superior, the thoracic inlet; inferior, the diaphragm. The sides are formed by the mediastinal pleurae. It is divided into superior and inferior mediastina by an imaginary line which extends from the sternal angle (manubriosternal joint) to the disk between the 4th and the 5th thoracic vertebrae. The inferior mediastinum is subdivided into 3 mediastina by the heart, which acts as the key structure in this subdivision. That part of the inferior mediastinum which contains the heart is called the middle mediastinum; that part in front of it makes up the anterior, and the part situated behind the heart constitutes the posterior mediastinum. Each of the 4 mediastina have their own boundaries.
The superior mediastinum contains: the arch of the aorta and its 3 branches (innominate, left common carotid and left subclavian arteries); the innominate veins; the upper half of the superior vena cava; the vagus, the phrenic and the left recurrent nerves; the esophagus, the trachea and the thoracic duct; the thymus or its remains in the adult with some lymph glands. The anterior mediastinum contains a few lymph glands (anterior mediastinal glands) and a little areolar tissue. The middle mediastinum contains: the heart enclosed in the pericardium; the ascending aorta; the lower half of the superior vena cava (with the azygos vein entering it); the bifurcation of the trachea; the pulmonary artery dividing into right and left branches; the right and the left pulmonary veins; the phrenic nerves; the bronchial lymph glands. The posterior mediastinum contains: the esophagus; the descending thoracic aorta; the vagi; the thoracic duct; the azygos; the hemiazygos and the accessory hemiazygos veins
DRAINAGE OF MEDIASTINAL ABSCESS Most mediastinal abscesses (mediastinitis) are drained through a right supraclavicular incision which is made in a transverse direction. This is deepened between the thyroid gland and the trachea medially, and the carotid sheath and the sternocleidomastoid muscle laterally. A finger is introduced along the right side of the esophagus and follows this downward until the abscess is reached and opened. Rarely is it necessary to perform an anterior or posterior mediastinotomy.
