Hemodynamic responses to two defibrillating trapezoidal waveforms

The purpose of this study is to compare postdefibrillation hemodynamics following a 2-msec 80% tilt shock to those following a 10-msec 50% tilt shock. The waveforms can be generated by an automatic implantable defibrillator. In 18 mongrel dogs, a defibrillating catheter carrying two pairs of electrodes was lodged at the apex of the right ventricle. Every 15 min a fibrillation-defibrillation episode was initiated, alternating the two defibrillating waveforms in successive episodes. The peak current for the 10-msec defibrillating shock was twice the predicted threshold peak current; the 2-msec shock was of the same delivered energy as the 10-msec shock. In each episode, fibrillation lated for 30 sec, then defibrillation was accomplished with one of the two wave-form countershocks. Hemodynamic measurements were recorded at 2 min prior to fibrillation and 1 min after defibrillation of each episode. Data were obtained on heart rate, mean femoral arterial blood pressure, cardiac output, left ventricular dP/dt, right ventricular dP/dt, cardiac power, and the number of ventricular ectopic beats per minute. The data indicate that with superior restoration of circulation as the criterion, a low-peak-current, long-duration, low-tilt defibrillating waveform is preferable for catheter-electrode ventricular defibrillation.