Demonstration of Posterior Atrial Input to the Atrioventricular Node During Sustained Anterograde Slow Pathway Conduction

Objectives. This study sought to demonstrate electrophysiologic evidence for the existence of different anatomic atrial input sites of fast and slow conduction pathways in patients with dual atrioventricular (AV) node physiology. Background. Although separate posterior exit site exists for retrograde slow AV node pathway, it remains unresolved whether separate atrial input site into the AV node actually exists in patients with dual anterograde AV node pathway physiology. Methods. In 10 patients with dual AV node pathway physiology, atrial pacing at three chosen drive cycle lengths (DCL1, DCL2 and DCL3) was performed at an anterior site (A) just above the His bundle recording site and at posterior atrial site (P) just below the coronary sinus ostium. DCL3 was chosen as the one cycle length that resulted in long AH interval consistent with slow pathway conduction. The stimulus to His bundle conduction times (SH) at both sites (SHP and SHA, respectively) and their differences (ΔSH = SHP − SHA) at each of the three drive cycle lengths were analyzed. Results. The mean ± SD ΔSH values for DCL1 and DCL2 measured 9 ± 16 and 8 ± 18 ms, respectively, and the mean ΔSH value at DCL3 measured −34 ± 24 ms, which was significantly different from the mean ΔSH values at DCL1 and DCL2 (both p < 0.05). Conclusions. The significant change in the ΔSH (SHP − SHA) value during slow pathway conduction could be accounted for by corresponding shift of anterograde input from an anterior to posterior entry site to the AV node. These findings support the notion that separate anterograde entry site of the slow pathway does exist in patients with dual AV node pathway physiology.