Bypass tracts revisited.

Abstract

The study of atrioventricular bypass tracts remains an educational cornerstone for students of electrophysiology seeking to understand the principles of reentry, mapping, tachycardia mechanism diagnosis in the electrophysiology laboratory, and ablation. Surgical and subsequently catheter ablation procedures to eliminate these tracts derived from an understanding of their anatomic location, typically bridging the atrioventricular annulus allowing conduction from atrium to ventricle to bypass the normal atrioventricular node. With this appreciation of anatomy and physiology, pacing maneuvers can be applied and interpreted to clarify the presence and electrophysiological properties of atrioventricular bypass tracts in the electrophysiology laboratory. Article see p 1262 In this segment of Teaching Points in Electrophysiology, Patel and colleagues1 present and carefully examine a different type of bypass tract, one connecting the right atrium to a pulmonary vein (PV) bypassing the left atrial myocardium. The underlying principle for PV isolation derives from the construct that the PV myocardium is solely activated via conduction from the left atrial myocardium across the PV ostium.2,3 The presence of an intercaval bundle creating a tract that electrically connects the posterior right atrium and the anterior aspect of the right superior PV makes isolation of this vein with left atrial ablation alone impossible. Similar tracts may also bypass the left atrium and connect a left PV to the coronary sinus (CS) musculature, to the left atrial appendage (LAA), or to an adjacent left PV. In the latter case, ostial encircling ablation lines will fail to isolate the vein. In the former 2 cases, even encircling antral ablation lines around the left PVs may fail to isolate these structures. In some patients, the remnant of the left superior vena cava—the ligament and vein of Marshall (VOM)—serves as the tract connecting the CS myocardium to a PV.2 The presence of these …