CHAPTER 78: ELECTROPHYSIOLOGIC ANATOMY

INTRODUCTION

Although the study of cardiac electrophysiology centers around the initiation of electrical impulses and their propagation, it is also very much an “anatomic specialty.” The study of electrophysiology requires critical appreciation and understanding of the anatomy of the heart and its relationship to electrophysiologic function. Over the past two decades, advances in electroanatomic mapping and cardiovascular imaging and innovations in both catheter ablation and device-based interventions have led to an improved understanding of cardiac anatomy, normal electrophysiologic function, and mechanisms behind heart rhythm disorders. Accordingly, describing cardiac structures in terms of their function and relationship to cardiac conduction¹ is much more useful to the clinical electrophysiologist than the conventional approach² of describing the heart in a purely anatomic and geographic fashion. This chapter on electrophysiologic anatomy highlights features of particular relevance in heart rhythm disorders.

THE HEART IN THE CHEST

For the clinician, the heart must be viewed in the context of its location and relationship to surrounding structures (Fig. 78–1). 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 often described as having three to four “moguls” on the chest x-ray, which correspond to the aortic arch, pulmonary artery, and left ventricle (superior to inferior). Occasionally, the left atrial appendage is visible between the pulmonary artery and the left ventricle. The aortic knob appears above the pulmonary trunk. In the hilum, the aortic knob is superior and rightward and the main pulmonary artery (or pulmonary trunk) is inferior and leftward. The pulmonary trunk crosses over the root of the aorta anteriorly such that the aorta ascends behind or posterior to it. On the frontal silhouette, the left atrium is barely seen; only its appendage curling round the edge of the pulmonary trunk is visible. The left atrium is the most posterior cardiac chamber (closest to the spine), and the esophagus is immediately behind the left atrium (Fig. 78–2). Understanding this spatial relationship is crucial to ablationists in order to reduce the risk of the postprocedural complication of atrioesophageal fistula.³