Transthoracic biphasic waveform defibrillation at very high and very low energies: a comparison with monophasic waveforms in an animal model of ventricular fibrillation.

The purpose of this study was to compare truncated exponential biphasic waveform versus truncated exponential monophasic waveform shocks for transthoracic defibrillation over a wide range of energies. Biphasic waveforms are more effective than monophasic shocks for defibrillation at energies of 150-200 Joules (J) but there are few data available comparing efficacy and safety of biphasic versus monophasic defibrillation at energies of <150 J or >200 J. Thirteen adult swine (weighing 18-26 kg, mean 20 kg) were deeply anesthetized and intubated. After 15 s of electrically-induced ventricular fibrillation (VF), each pig received truncated exponential monophasic shocks (10 ms) and truncated exponential biphasic shocks (5/5 ms) in random order. Energy doses ranged from 70 to 360 J. Success was defined as termination of VF at 5 s post-shock. For both biphasic and monophasic waveforms success rate rose as energy was increased. Biphasic waveform shocks (5/5 ms) were superior to 10 ms monophasic waveform shocks at the very low energy levels (at 70 J, biphasic: 80+/-9%, monophasic; 32+/-11% and at 100 J, biphasic; 96+/-3% and monophasic 39+/-11%, both P < 0.01). No significant differences in shock success were seen between biphasic and monophasic waveform shocks at 200 J or higher energy levels. Shock success of > 75% was achieved with 200 J (10 J/kg) for both waveforms. Pulseless electrical activity (PEA) or ventricular asystole occurred in 4 animals receiving monophasic shocks and 1 animal receiving biphasic shocks. Biphasic waveform shocks (5/5 ms) for transthoracic defibrillation were superior to monophasic shocks (10 ms) at low energy levels. Percent success increased with increasing energies. PEA occurred infrequently with either waveform.