Transepicardial Defibrillation Dose Response: Current Versus Energy

In pentobarbital-anesthetized dogs, we compared the relative efficacy of current versus energy in applying the dose response method in transcardiac defibrillation. Damped sinusoidal shocks via epicardial patches were administered by a custom defibrillator permitting precise current delivery. Following the establishment of an initial estimated defibrillation threshold for energy and current, the dose response method was performed with regard to either energy defibrillation threshold (group E, n = 8) or current defibrillation threshold (group C, n = 8). Two sequential sets (I, II) of shocks (21 shocks each) were delivered in random order at each of seven doses: 0.55, 0.70, 0.85, 1.00, 1.15, 1.30, and 1.45 × defibrillation threshold. Data were subjected to nonlinear logistic regression analysis. There were no significant differences between sets I and II in either groups E or C for resistance or for raw and normalized values associated with 50% and 80% success expressed as energy, current, or voltage. Correlation coefficients (r) associated with nonlinear logistic regression analysis were significantly different for normalized current and energy for group E (0.70 ± 11 and 0.71 ± 12) compared to group C (0.86 ± 0.60 and 0.88 ± O.0.6). The difference. however, could be explained by a significantly narrower range of normalized current values tested in group E (0.79 to 1.31) versus group C (0.54 to 1.46). Thus, when resistance does not change, transcardiac current offers limited advantage over energy when applying a dose response method. The efficacy of nonlinear logistic regression analysis depends upon an adequate dose range.