Abstract 12422: Does a Jump in the Atrioventricular Conduction Curve Really Indicate a Switch From Fast Pathway to Slow Pathway Conduction?

Introduction: A jump in the atrioventricular (AV) conduction curve (aka, a discontinuous curve) remains the current clinical criterion for diagnosing dual pathway AV nodal electrophysiology. However, it has never been proven that a jump in the AV conduction curve indicating a transition from fast pathway (FP) to slow pathway (SP) conduction, as it has been assumed.

Hypothesis: A jump in the AV conduction curve may not reflect the transition from FP to SP conduction, as assumed it does by the current clinical criterion.

Methods: Eighty-one experimental records from rabbit AV nodal preparations containing the following data were analyzed. 1. had at least one AV conduction curve, and 2. had intracellular action potential recordings from AV nodal fibers and/or recording of His electrogram alternans (a validated new index of dual pathway conduction).

Results: There were 11 (13%) of 81 preparations showing a jump in the AV conduction curve. In these preparations, the transition from FP to SP conduction was smooth. The jumps always occurred after the FP to SP transition at a much shorter prematurity (Figure). On average, the FP-SP transition occurred at prematurity of 196±39ms versus the jump at 117±9ms (P<0.001). Complex intranodal/nodal-atrial reentries were detected after the FP to SP transition. The jumps were always associated with and most likely caused by the intranodal/nodal-atrial reentry and its subsequent conduction to the His bundle, rather than a direct conduction by the premature beat itself.

Conclusions: The transition from FP to SP conduction does not produce a jump in the AV conduction curve. A jump in the AV conduction curve is likely caused by induction of intranodal/nodal-atrial reentry by the premature beat and the subsequent conduction of the reentrant beat to the His bundle, rather than a direct conduction by the premature beat itself. Thus, a jump in the AV conduction curve as the current clinical criterion of dual pathway conduction should be invalidated.