Chapter 37

Rapid advances have been made in electrophysiologic mapping, imaging, use of catheter ablations for drug refractory arrhythmias, and transcatheter implantation of pacing leads. A better understanding of cardiac anatomy is essential to make further progress, especially in fine-tuning interventional techniques and in developing computer models of arrhythmias. To this end, describing cardiac structures in attitudinal perspective1 is much more useful to the clinical electrophysiologist than the conventional approach2 of describing the heart as if it is standing on its apex and rotated with right and left heart chambers side by side. This chapter on cardiac anatomy highlights features of particular relevance to electrophysiologists.

For the clinician the heart must be viewed in the context of its location and relationship to surrounding structures. The frontal silhouette of the heart is nearly trapezoidal. The right border of the heart is more or less a vertical line just to the right of the sternum. It is formed exclusively by the right atrium, with the superior and inferior caval veins joining at its upper and lower margins. The inferior border lying horizontally on the diaphragm is marked by the right ventricle. The sloping left border is made up of the left ventricle and, as it merges with the upper border, the silhouette is formed by the pulmonary trunk. The upper border of the silhouette is made by the arterial trunks with the pulmonary valve leftward and superiorly situated relative to the aortic valve. On the frontal silhouette, the left atrium is barely seen; only its appendage curling round the edge of the pulmonary trunk is visible. Thus, the left atrium is the most posteriorly situated cardiac chamber. When viewed in situ, the proximity of the esophagus to the posterior wall of the left atrium is clear (Fig. 37–1). This spatial relationship is crucial to ablationists in order to reduce the risk of the post-procedural complication of atrioesophageal fistula.3,4

###### Figure 37–1

Two halves of the same specimen bisected longitudinally to show the relationship between the posterior wall of the left atrium and the esophagus. Ao, aorta; Es, esophagus; LA, left atrium; LAA, left atrial appendage; LI, left inferior pulmonary vein; LS, left superior pulmonary vein; MV, mitral valve; RI, right inferior pulmonary vein; RS, right superior pulmonary vein.

The heart is enclosed in a fibrous sac, the pericardium, which separates the surface of the heart from adjacent structures. The mediastinal pleura is the outermost lining of the fibrous pericardium. Within the fibrous pericardium there is a thinner double-layered membrane, the serous pericardium. One layer of the serous pericardium is fused to the inner surface of the fibrous pericardium while the other layer lines the outer surface of the heart as the epicardium. The pericardial cavity then is the space between the layers of the serous pericardium. Two recesses are found within the pericardial ...

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