Abstract 9386: Ramp Biphasic Waveforms Have a Lower External Defibrillation Threshold

Abstract

Introduction: We have previously shown that waveforms with an ascending ramp in both phases have a lower internal defibrillation threshold (DFT). The purpose of this study was to test whether waveforms with rectilinear, ascending and descending ramps in the second phase would reduce the DFT compared with a standard exponential biphasic waveform with external defibrillation shocks. Methods: In 6 pigs, DFTs were determined for 10 waveforms: a standard truncated exponential biphasic waveform with 60% tilt (Fig 1, #1) and 9 biphasic waveforms with an 8 ms ascending ramp 1st phase and one of 3 rectilinear, ascending ramp or descending ramp 2nd phases. The 3 rectilinear 2nd phases were: 1 ms, 200% of peak voltage of phase 1 (#2); 2 ms, same voltage as phase (#3); 3 ms, half the voltage of phase 1 (#4). The 3 ascending ramp 2nd phases were: 2 ms, 200% of voltage of phase 1(#5); 3 ms, same voltage as phase 1(#6); 4.5 ms, half the voltage of phase 1(#7). The 3 descending ramp 2nd phases were: 2 ms, 200% of voltage of phase 1(#8); 3 ms, same voltage as phase 1(#9); 4.5 ms, half the voltage of phase 1(#10). Results: Phase 2 ascending ramp (#7) and descending ramp (#8, #9) waveforms had the lowest DFTs, which were significantly smaller than for the truncated exponential waveform. (Fig 1, *indicates p<0.05). Conclusions: Waveforms with a ramp in phase 2 (#7, #8, #9) have a lower DFT.