Comparison of the efficacy of defibrillation with the damped sine and constant-tilt current waveforms in the intact animal.

The efficacy of defibrillation using the damped sine and constant-tile (60%) truncated exponential waveforms was determined in each of nine dogs. Two measures of efficacy were used to compare the two waveforms: 1) threshold defibrillation current and 2) percent successful defibrillation. For both measures of efficacy, shock strength was expressed in terms of delivered energy. Mean threshold energy was 0.98 J/kg for the damped sine wave and it was 1.24 J/kg for the truncated exponential waveform. Percent successful defibrillation versus energy/kg curves were constructed for each of the waveforms and were found to be essentially the same. Percent successful defibrillation increased with increasing shock intensity. For 50% success, the energy for the damped sine wave was 1.16 J/kg; for the truncated exponential wave, the corresponding value was 1.15 J/kg. A shock of threshold intensity successfully defibrillated in approximately 50% of the defibrillation attempts, i.e., defibrillation threshold corresponds to about 50% successful defibrillation.