DISCOVERY OF A NEW INDEX OF DUAL PATHWAY ATRIOVENTRICULAR NODE CONDUCTION
Youhua Zhang, M.D., Ph.D.,
New York Institute of Technology (NYIT) College of Osteopathic Medicine, Old Westbury, NY, USA
Dual pathway atrioventricular (AV) node electrophysiology is the basis of AV nodal reentrant tachycardia (AVNRT). Current clinical criterion for dual pathway conduction is a discontinuity or “jump” in the AV conduction curve. Although it is intuitive that a “jump” in the AV conduction curve indicates a switch from fast pathway to slow pathway conduction, this is only speculation. In addition, the criterion cannot be used to monitor dual pathway conduction on a beat by beat basis. Over the years, we have discovered and validated in rabbit hearts that dual pathway AV conduction results in a new phenomenon, originally termed His electrogram alternans (recently renamed Zhang’s phenomenon). It is found that His electrogram recorded from the superior His bundle domain (superior His electrogram) is high-in-amplitude at basic beats and long coupling intervals (i.e., fast pathway conduction) and low-amplitude at short prematurities (i.e., slow pathway conduction). In contrast, His electrogram recorded from the inferior His bundle domain (inferior His electrogram) is always from low-amplitude during fast pathway conduction to high-amplitude during slow pathway conduction. This novel index permits monitoring AV conduction pattern (through the fast or slow pathway) on a beat by beat basis in various conditions, either at a single premature beat, during fast regular rates or even during atrial fibrillation. We have demonstrated recently that dual pathway conduction produces functional dissociation in the distal node, resulting in superior-fast and inferior-slow dual inputs into the His bundle, which is the electrophysiological basis for the formation of this new phenomenon during dual pathway conduction. The phenomenon has been replicated by other investigators in rabbit hearts as well as in isolated human hearts. However, clinical feasibility studies to record this phenomenon remain needed before this novel index can be applied in patients during cardiac electrophysiology studies.