Surgical anatomy of the conduction system

Summary

The disposition of the conduction system in the normal heart has been emphasised already (see Chapter 2). In that earlier chapter, we pointed to the importance, during surgical procedures, of avoiding the cardiac nodes and ventricular bundle branches, and scrupulously protecting the vascular supply to these structures. In this chapter, we will consider the anatomy of these tissues relative to the treatment of intractable problems of cardiac rhythm. The abnormal dispositions of the conduction tissue to be found in congenitally malformed hearts, features of obvious significance to the congenital cardiac surgeon, will be discussed in the sections devoted to those lesions in the chapters that follow. In this chapter, nonetheless, we will discuss surgical procedures performed to treat arrhythmias that develop in the setting of the Fontan circulation.

LANDMARKS TO THE ATRIOVENTRICULAR CONDUCTION AXIS

In patients with intractable tachycardia, it may be necessary to ablate the atrioventricular bundle. Although this sometimes occurs inadvertently, it can be surprisingly difficult to divide this structure intentionally. The landmark to penetration of the atrioventricular conduction axis through the fibrous insulating plane is the apex of the triangle of Koch (Figure 5.1). The apex is marked by the point at which the tendon of Todaro inserts into the central fibrous body (Figure 5.2). Just inferior to the apex of this triangle, the components of the atrioventricular node gather themselves together, and enter the insulating tissues of the fibrous body (Figures 5.3, 5.4). Once insulated from the atrial myocardial mass, the conduction axis becomes the penetrating atrioventricular bundle, better known as the bundle of His. This part of the overall atrioventricular conduction axis is short, but extends leftwards as it pierces the fibrous body.