Correlation between shock induced response duration and success of defibrillation

Although refractory period extension has been proposed as a basic mechanism for defibrillation, the relation between successful defibrillation and refractory period extension has not been determined. The authors tested the hypothesis that successful defibrillation correlates with longer shock induced responses compared with unsuccessful defibrillation. Sixty five episodes of fibrillation were induced in isolated rabbit hearts (n=5). After 10 seconds of fibrillation, defibrillation was attempted with 8 msec monophasic pulses (65% tilt) using epicardial patches. Action potentials were recorded with MAPs placed perpendicular to the shocking electrodes. Response duration measured from the beginning of the shock to maximal repolarization of the action potential was 96.5±14 msec during successful defibrillation and 54±25 msec during unsuccessful defibrillation (p<0.01). The authors´ results suggest that the extension of refractoriness by the defibrillating shock determines the success of defibrillation