Previous studies have established efficacy of transseptal defibrillation. The purpose of the present study was to evaluate the role of transvenous electrode surface area for defibrillation. Sixteen dogs were randomized to 8 French and 5 French EnGuard electrodes; 8 dogs in each group. The length of the defibrillation coils was identical for both, but the surface area was different due to differences in the electrode diameters. Defibrillation threshold (DFT) testing was performed using a biphasic shock waveform, 6 msec+/2msec-. Logistic regression analysis was used to determine if the probability of defibrillation adjusted for voltage, current, and energy was different for 8 French electrodes. Logistic regression analysis found significant differences between 8 French and 5 French electrodes, with less voltage (P < 0.005), current (P < 0.03), and energy (P < 0.001) required at any level of probability to defibrillate for 8 French electrodes. These results support the conclusion that the surface area for endocardial electrodes is a significant factor for defibrillation. Therefore, when designing endocardial electrodes a desirable objective of reducing the electrode size should be weighed against the need to minimize DFTs.
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