(Circulation. 1996;94:2278-2284.)
© 1996 American Heart Association, Inc.
Articles |
Charge-Burping Theory Correctly Predicts Optimal Ratios of Phase Duration for Biphasic Defibrillation Waveforms
the Division of Cardiology, Cedars-Sinai Medical Center, Los Angeles, Calif.
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 (
s) exceeds the time constant of the cell membrane (m) but >1 when s<m. This study tested the hypothesis that the optimal phase-duration ratio depends on 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, s=7.1±0.8 ms) and very small capacitors (40 µF, 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.
Key Words: defibrillation • charge burping • waves
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