Session S43.3

Transmission Characteristics at Purkinje-Myocardial Junctions Are Affected by Defibrillation-Strength Shocks

PM Boyle*, EJ Vigmond

University of Calgary
Calgary, Alberta, Canada

In normal cardiac function, the orderly activation of the heart is facilitated by the Purkinje System (PS), a specialized network of fast-conducting fibers that lines the ventricles. Experimental findings suggest that many junctions between the PS and surrounding myocardial tissue (PMJs) remain functionally quiescent during typical heart beats because of electrical coupling characteristics. While computer modeling studies have demonstrated that the PS can play a significant role in determining the response of the quiescent ventricles to defibrillation-strength shocks, it is not known whether this sort of stimulation alters PMJ transmission characteristics.
We hypothesized that shock-induced current in the PS increases the likelihood and rapidity of PMJ transmission by mitigating the severity of the source-sink mismatch between the PS and coupled myocytes. Several shocks in the defibrillation range were applied to a model of rabbit ventricles and the PS calibrated to reproduce sinus rhythm. PMJ transmission was inspected at individual junctions and at the systemic level to assess whether shocks increased the viability of propagation and whether anterograde propagation delay was abbreviated. Comparing His bundle stimulation to a 10 V/cm shock along the primary cardiac axis, the number of quiescent PMJs was reduced by 82% and the average propagation delay was reduced by 57%. These findings indicate that PMJ transmission characteristics are altered during the application of shocks, which suggests possible increased efficacy for therapies that consider the role of the PS during defibrillation.

(Abstract Control Number: 140)