Schedule Aug 21, 2003
Dynamic Mechanism for Conduction Block in Heart Tissue
Robert Gilmour (Cornell University)

Induction of the spiral wave reentry that underlies certain cardiac rhythm disturbances requires wave break, secondary to the development of local conduction block. The latter may be the consequence of a period doubling bifurcation of cellular electrical properties, manifest as electrical alternans. Previous theoretical and experimental work has characterized the transition from concordant and discordant alternans to conduction block and the extent to which a nonlinear-dynamical control algorithm suppresses alternans in a spatially distributed system. Although valuable for identifying underlying dynamic mechanisms for conduction block, these studies have been conducted during prolonged high frequency pacing, which may not replicate the typical clinical scenario in which a normal cardiac rhythm is interrupted by only a few premature beats. To address this issue, we recently investigated the mechanism for conduction block following the delivery of 1-4 premature stimuli using a coupled maps computer model of a 1D canine heart fiber and experiments in isolated cardiac fibers and intact hearts. The coupled maps model allowed us to identify the roles that velocity (V) restitution, action potential duration (D) restitution, and cardiac memory (M) played in the development of spatial heterogeneity and conduction block. We found that the likelihood of conduction block could be reduced by three methods. 1) By altering the V restitution function so that conduction slowed at very short rest intervals (I). 2) By altering the D restitution function to reduce the sensitivity of D on I. 3) By increasing the contribution of cardiac memory (M). These results suggest several potential interventions that may reduce the probability of arrhythmia induction.

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