Biphasic Waveform Better Than Monophasic in Defibrillation

Biphasic waveform, automated, external defibrillators (AEDs) are rapidly becoming the standard because they are smaller and lighter than monophasic AEDs. These authors compared defibrillation with an impedance-compensated, biphasic, truncated, exponential waveform; a monophasic, truncated, exponential waveform; and a monophasic, damped-sine waveform in a trial supported by the manufacturer of the biphasic AED.

The type of AED used was randomized on a daily basis. Monophasic AEDs delivered 200, 200, and 360 J. The biphasic machine delivered 150 J adjusted for patient impedance. Data were analyzed for 115 patients who presented with ventricular fibrillation and had arrest secondary to cardiac etiology. Defibrillation (conversion to any other rhythm) was achieved with 3 or fewer shocks in 98 percent of patients treated with the biphasic waveform, compared with 67 percent of those treated with the monophasic, truncated, exponential waveform (P < 0.0001) and 77 percent of those treated with the monophasic, damped-sine waveform (P < 0.021). The rate of return of spontaneous circulation (ROSC) was 76 percent with the biphasic waveform and 54 percent with both the truncated, exponential and damped-sine, monophasic waveforms. Survival to discharge did not differ significantly (28 percent, 35 percent, and 15 percent, respectively) among the methods.

Comment: This study supports previous small studies suggesting that the biphasic defibrillation waveform is superior. There was a 21 percent to 31 percent absolute improvement in the rate of defibrillation achieved with 3 or fewer shocks and a strong trend toward improved ROSC. Larger randomized trials are needed to determine whether the rate of survival to discharge is increased with biphasic waveform use.

— JM Christenson

Published in Journal Watch Emergency Medicine October 4, 2001

Source

Martens PR et al. Optimal response to cardiac arrest study: Defibrillation waveform effects. Resuscitation 2001 Jun 49 233-243.