Comparative efficacy of monophasic and biphasic truncated exponential shocks for nonthoracotomy internal defibrillation in dogs

Abstract

Pentobarbital-anesthetized dogs were studied to determine the relative efficacy of monophasic and biphasic truncated exponential shocks employing a nonthoracotomy internal defibrillation pathway that consisted of a right ventricular catheter electrode (cathode) and a subcutaneous chest wall patch electrode (anode). In part 1 of the experiments, six dogs (19.6 ± 1.1 kg) were utilized. Monophasic pulses of 5, 7.5, 10 and 12.5 ms duration were compared with biphasic pulses of the same total duration. The biphasic pulses had an initial positive phase (P1) followed by a terminal negative phase (P2) with the initial voltage equal for each phase. For each biphasic total pulse width, five relative P1versus P2durations were tested (50 and 50%, 75 and 25%, 90 and 10%, 25 and 75%, 10 and 90%). Ventricular fibrillation was induced by alternating current and pulse configurations were tested randomly to determine the minimal voltage and energy for defibrillation (threshold). Biphasic shocks with P1longer than P2were associated with significantly tower (p < 0.01) energy thresholds than were monophasic shocks. Additionally, there was no significant relation between pulse width and voltage or energy thresholds.In part 2 of the experiments, six dogs (20.2 ± 1.6 kg) were studied. Monophasic shocks were compared with biphasic shocks with P1versus P2durations of 75 aud 25% and 90 and 10% for total puke widths of 7.5, 10 and 12.5 ms. Threshold determinations were performed as in part 1. Subsequently, five initial voltages clustered about threshold were randomly tested four times and dose-response curves constructed for each pulse configuration with the use of stepwise logistic regression. Biphasic shocks resulted in significantly lower energy (p < 0.0001) and voltage (p < 0.001) requirements than did monophasic shocks. There was no difference in energy requirements between the 75 and 25% and 90 and 10% biphasic shocks, although the 75 and 25% shocks were associated with significantly lower (p < 0.001) voltage requirements than the 90 and 10% shocks.These results indicate that biphasic shocks with P1(initial positive phase) longer than P2(terminal negative phase) markedly reduce energy requirements for nonthoracotomy canine defibrilation and may, therefore, facilitate development of nonthoracotomy devices for clinical application.