Abstract P132: The Optimal Second Phase Duration for Biphasic Truncated Exponential Waveform Defibrillation
Introduction For termination of ventricular fibrillation (VF), biphasic waveforms have proven more effective than monophasic waveforms. As yet not well defined is the optimal second (negative) phase duration. We therefore examined the best negative phase and comprising delivered energy and peak current based on the measurement of defibrillation threshold.
Methods In 10 domestic pigs weighing between 35– 45 (40±3) kg, VF was electrically induced and untreated for 15 seconds. First (positive) phase was maintained in the range of 4.04±0.01ms. Second phase was randomizely adjusted to 1.02, 1.36, 2.04, 3.06 and 6.12 ms utilizing a Philips MRx defibrillator to allow variable duration of the second phase. The 80% defibrillation threshold (DFT80) served to defined optimal duration of the second phase where delivered energy was varied between 72 and 188 Joules.
Results The energy was minimal when the second phase duration ranged between 1.36 to 3.06 ms (Figure 1⇓). The peak current was significantly lower when the second phase duration was 3.06 ms, which corresponded to a delivered peak current of 29 Amps.
Conclusion When the first phase of a biphasic waveform was maintained at a fixed duration of 4 ms, the optimal second phase duration is approximately 3 ms in this experimental setting.