Chapter 55 Applied Anatomy of the Heart and Great Vessels Joseph G. Murphy, M.D. Pericardium This chapter reviews important topics in cardiovas- cular anatomy that pertain to the practice of clinical The pericardium surrounds the heart and consists of fibrous cardiology. The format of the chapter is to describe and serous portions. The fibrous pericardium forms a tough briefly the anatomy followed by the clinical signifi- outer sac, which envelops the heart and attaches to the great cance in italic type. vessels. The ascending aorta, pulmonary artery, terminal 2 to 4 cm of superior vena cava, and short lengths of the pulmonary veins and inferior vena cava are intrapericardial (Fig. 1). Mediastinum The fibrous pericardium is inelastic and limits the diastolic distention of the heart during exercise. Cardiac enlarge- The mediastinum contains, in addition to the heart and great ment or chronic pericardial effusions, both of which develop vessels, the distal portion of the trachea, right and left bronchi, slowly, will stretch the fibrous pericardium. However, the esophagus, thymus, autonomic nerves (cardiac and splanch- fibrous pericardium cannot stretch acutely, and the rapid nic, left recurrent laryngeal, and bilateral vagal and phrenic), accumulation of as little as 200 mL of fluid may produce various small arteries (such as bronchial and esophageal) and fatal cardiac tamponade. Hemopericardium results from veins (such as bronchial, azygos, and hemiazygos), lymph perforation of either the heart or the intrapericardial great nodes, cardiopulmonary lymphatics, and thoracic duct. vessels. Enlargement of a cardiac chamber or great vessel may dis- The serous pericardium is a delicate mesothelial layer place or compress an adjacent noncardiac structure. An that lines the inner aspect of the fibrous pericardium (pari- enlarged left atrium may displace the left bronchus superior- etal pericardium) and the outer surface of the heart and ly and the esophagus rightward. An aberrant retroesophageal intrapericardial great vessels (visceral pericardium). The right subclavian artery indents the esophagus posteriorly and visceral pericardium, or epicardium, contains the coronary may cause dysphagia. Mediastinal neoplasms can compress arteries and veins, autonomic nerves, lymphatic channels, the atria, superior vena cava, or pulmonary veins. and variable amounts of adipose tissue. Sections of the text in italic type are topics related to pathology. An atlas illustrating the anatomy of the heart is at the end of the chapter (Plates 1-24). Modified from Edwards WD: Applied anatomy of the heart. In Giuliani ER, Gersh BJ, McGoon MD, Hayes DL, Schaff HV (editors): Mayo Clinic Practice of Cardiology. Third edition. Mosby, 1996, pp 422-489. By permission of Mayo Foundation. 927 928 Applied Anatomy of the Heart and Great Vessels S Parietal pericardium Ao V Ao PA C PA SVC L P R V P V RA RV IVC A Diaphragm B Fig. 1. Parietal pericardium. A, Anterior portion of the parietal pericardium has been removed to show the intrapericardial segments of the great arteries and superior vena cava. (Anterior view from 16-year-old boy.) B, Heart has been removed from posterior portion of parietal pericardium to show the great ves- sels, the transverse sinus (dashed line), and the oblique sinus (arrows). (Anterior view from 13-year-old boy.) (See Appendix at end of chapter for abbre- viations.) (A from Mayo Clin Proc 56:479-497, 1981. By permission of Mayo Foundation.) In obese subjects, excessive epicardial depot fat may organization of such an exudate may result in fibrous adhe- encase the heart, but because pericardial fat is liquid at sions between the epicardium and the parietal pericardium. body temperature, cardiac motion is generally unhindered. Focal adhesions are usually unimportant, but occasionally Focal epicardial fibrosis along the anterior right ventricle they may allow the accumulation of loculated fluid or, rarely, or posterobasal left ventricle (so-called soldiers’ patches) tamponade of an individual cardiac chamber, usually the may result from old pericarditis or perhaps from the trauma right ventricle. After cardiac surgery, the opened pericardial of an enlarged heart’s impact against the sternum or calcified cavity may become sealed again if the parietal pericardium descending thoracic aorta. adheres to the sternum; in this setting, the raw pericardial sur- Between the great arteries (aorta and pulmonary artery) faces, which are lined by fibrovascular granulation tissue, and the atria is a tunnel-like transverse sinus (Fig. 1). may ooze enough blood to cause cardiac tamponade. Posteriorly, the pericardial reflection forms an inverted U- Densely fibrotic adhesions, with or without calcification, shaped cul-de-sac known as the oblique sinus. The liga- can hinder cardiac motion and may restrict cardiac filling. ment of Marshall is a pericardial fold that contains the The pericardium is thickened in subjects with chronic con- embryonic remnants of the left superior vena cava. striction but not necessarily so in persons with constriction that A sequential saphenous vein bypass graft to the left coro- develops relatively rapidly. In the setting of constrictive peri- nary system may be positioned posteriorly through the trans- carditis, surgical excision of only the anterior pericardium verse sinus. A persistent left superior vena cava will occupy (between the phrenic nerves) is often inadequate, because the expected site of the ligament of Marshall, along the junc- the remaining pericardium surrounds enough of the heart to tion between the appendage and body of the left atrium. maintain constriction. Between the parietal and visceral layers of the serous peri- Most postoperative pericardial adhesions are usually cardium is the pericardial cavity, which normally contains functionally unimportant, but they may obscure the location 10 to 20 mL of serous fluid that allows the tissue surfaces of the coronary arteries at subsequent cardiac operation. to glide over each other with minimal friction. Other pericardial conditions include congenital cysts or Thick and roughened surfaces associated with fibri- diverticula of the pericardium, or the parietal pericardium nous pericarditis lead to an auscultatory friction rub, and may be focally deficient or absent. Applied Anatomy of the Heart and Great Vessels 929 G The fibrous pericardium cannot adequately stretch acutely, and the rapid accumulation of as little as 200 mL of fluid may produce fatal cardiac tamponade. G A sequential saphenous vein bypass graft to the left coro- nary system may be positioned posteriorly through the transverse sinus. Great Veins Bilaterally, the subclavian and internal jugular veins merge to form bilateral innominate (or brachiocephalic) veins. The latter then join to form the superior vena cava (or superior caval vein) (Fig. 2). Superior Vena Cava The right internal jugular vein, right innominate vein, and superior vena cava afford a relatively straight intravascular route to the right atrium and tricuspid orifice. Accordingly, this route may be used for passage of a stiff endomyocardial bioptome across the tricuspid valve and into the right ventricular apex to obtain a cardiac biop- sy specimen. Similarly, both temporary and permanent transvenous pacemaker leads are inserted via either the subclavian or the internal jugular vein and are threaded into the right ventricular apex. Catheters and pacemakers within the innominate veins and superior vena cava become partially coated with thrombus and may be associated with thrombotic venous obstruction, pulmonary thromboembolism, or secondary Fig. 2. Systemic veins, excluding the portal circulation. (See Appendix at infection. Mediastinal neoplasms, fibrosis, and aortic end of chapter for abbreviations.) aneurysms may compress the thin-walled veins and result in the superior vena caval syndrome. Renal cell carcinomas may extend intravascularly within Inferior Vena Cava the renal veins and inferior vena cava and may even form The inferior vena cava receives systemic venous drainage tethered intracavitary right-sided cardiac masses. from the legs and retroperitoneal viscera and, at the level Hepatocellular carcinomas often involve the hepatic veins of the liver, from the intra-abdominal systemic venous and occasionally may enter the suprahepatic inferior vena drainage (portal circulation) via the hepatic veins. cava or right atrium. The inferior vena cava, which is retroperitoneal, may The superior and inferior pulmonary veins from each become trapped and compressed between the vertebral lung enter the left atrium. The proximal 1 to 3 cm of the column posteriorly and either an adjacent retroperitoneal pulmonary veins contain cardiac muscle within the media structure (for example, an abdominal aortic aneurysm) or and may thereby function like sphincters during atrial sys- an intraperitoneal structure (for example, a neoplasm) and tole as well as when significant mitral valve disease exists. thereby produce the inferior vena caval syndrome. The thin-walled and low-pressure pulmonary veins may Venous thrombi in the lower extremities may extend into be compressed extrinsically by mediastinal neoplasms or the inferior vena cava or may become dislodged and fibrosis. Rarely, a primary neoplasm may cause luminal embolize to the right heart and pulmonary circulation. obstruction in the major pulmonary veins. 930 Applied Anatomy of the Heart and Great Vessels Congenital Abnormalities of the Venous System Cardiac Chambers Congenital anomalies of