ELECTROPHYSIOLOGICAL BACKGROUND OF INDIVIDUAL VARIABILITY IN ELECTRICAL DEFIBRILLATION EFFICACY

This study was performed to test whether heart-to-heart variability of defibrillation efficacy is attributable to differences in postshock r efractory state of nondepolarized myocardium. In 30 anesthetized dogs, a localized potential gradient was created using 1-16 V of stimulus a cross a pair of platinum plate electrodes on the right ventricle (5-mm interelectrode distance). The postshock recovery interval (PSRI) of t he relatively refractory myocardium directly adjacent to the excited a rea was estimated by measuring the recovery interval after an appropri ately timed field stimulus. The transcardiac defibrillation threshold (DFT) was also determined. The results showed that DFT normalized by t he weight of the heart was inversely correlated with the PSRI measured with a field stimulus of 6 V (local shock intensity similar to 5 V/cm ) or more (6 V: r = -0.502, P < 0.005; 16 V: r = -0.635, P < 0.0005). This observation suggests that variability of defibrillation efficacy in intact hearts is largely due to differences in the postshock refrac tory state of the nondepolarized myocardium.