DEMONSTRATION OF A POSTERIOR ATRIAL INPUT TO THE ATRIOVENTRICULAR NODE DURING SUSTAINED ANTEROGRADE SLOW PATHWAY CONDUCTION

Objectives. This study sought to demonstrate electrophysiologic eviden ce for the existence of different anatomic atrial input sites of fast and slow conduction pathways in patients,vith dual atrioventricular (A V) node physiology. Background. Although a separate posterior exit sit e exists for a retrograde slow AV node pathway, it remains unresolved whether a 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 a t a posterior atrial site (P) just below the coronary sinus ostium, DC L3 was chosen as the one cycle length that resulted in a long AH inter val consistent with slow pathway conduction, The stimulus to His bundl e conduction times (SH) at both sites (SHP and SHA, respectively) and their differences (Delta SH = SHP - SHA) at each of the three drive cy cle lengths were analyzed. Results. The mean +/- SD Delta SH values fo r DCL1 and DCL2 measured 9 +/- 16 and 8 +/- 18 ms, respectively, and t he mean Delta SH value at DCL3 measured -34 +/- 24 ms, which was signi ficantly different from the mean Delta SH values at DCL1 and DCL2 (bot h p < 0.05). Conclusions. The significant change in the Delta SH (SHP - SHA) value during slow pathway conduction could be accounted for by a corresponding shift of anterograde input from an anterior to a poste rior entry site to the AV node. These findings support the notion that a separate anterograde entry site of the slow pathway does exist in p atients with dual AV node pathway physiology. (C) 1998 by the American College of Cardiology.