Charge-Burping Theory Correctly Predicts Optimal Ratios of Phase Duration for Biphasic Defibrillation Waveforms

Abstract

Background For biphasic waveforms, it is accepted that the ratio of the duration of phase 2 to the duration of phase 1 (phase-duration ratio) should be ≤1. The charge-burping theory postulates that the beneficial effects of phase 2 are maximal when it completely removes the charge delivered by phase 1. It predicts that the phase-duration ratio should be <1 when the time constant of the defibrillation system (τ s ) exceeds the time constant of the cell membrane (τ m ) but >1 when τ s <τ m . This study tested the hypothesis that the optimal phase-duration ratio depends on τ s (the product of the defibrillator capacitance and pathway resistance). Methods and Results In a canine model of transvenous defibrillation (n=8), we determined stored-energy defibrillation thresholds (DFTs) for biphasic waveforms from conventional capacitors (140 μF, τ s =7.1±0.8 ms) and very small capacitors (40 μF, τ s =2.0±0.2 ms). Each capacitance was tested with phase-duration ratios of 0.5, 1, 2, and 3. The duration of phase 1 approximated the optimal monophasic waveform, 6.3±0.7 ms for 140-μF waveforms and 2.8±0.2 ms for 40-μF waveforms. For 140-μF waveforms, the DFT was lower for phase-duration ratios ≤1 than for phase-duration ratios >1 ( P =.0003). The reverse was true for 40-μF capacitors ( P =.0008). There was a significant interaction between the effects of capacitance and phase-duration ratio on DFT ( P =.0002). The lowest DFT for 40-μF waveforms was less than the lowest DFT for 140-μF waveforms (4.9±2.5 versus 6.4±2.4 J, P <.05). Conclusions The optimal phase-duration ratio is ≤1 for conventional capacitors and >1 for small capacitors. This supports the predictions of the charge-burping theory.