Purpose: Conventional biphasic truncated exponential (BTE) waveforms have been studied extensively but less is known about "chopping modulated" BTE shocks. Previous studies comparing chopped and unchopped waveforms have found conflicting results. This study compared the defibrillation thresholds (DFTs) of a variety of chopped and unchopped BTE waveforms.
Methods: Six anesthetized pigs were defibrillated after 15s of electrically induced ventricular fibrillation (VF). Three waveform types were studied: unchopped BTE, "short" duration chopped, and "long" duration chopped waveforms. Each type included waveforms generated with 50, 100, and 200 microF capacitances, giving 9 total waveforms. Shocks were delivered in a standard up-down protocol and the order of the waveforms was randomized. Defibrillation thresholds were calculated using a Bayesian logistic regression model.
Results: DFTs of the 50, 100, and 200 microF unchopped waveforms were 122+/-22, 124+/-22, and 126+/-22 J. Short chopped DFTs were at least 75+/-23 J higher than unchopped DFTs. Long chopped DFTs averaged 66+/-20 J more than short chopped DFTs. There is a 99.5% probability that the best of the chopped waveforms has a higher DFT than the worst of the unchopped waveforms, and a 95% probability that the difference is at least 37 J. DFT differences between capacitor values were less than 7 J for all waveform types.
Conclusions: When treating swine with short-duration VF, chopped waveforms require more energy to defibrillate than unchopped waveforms. More study is required to assess the performance of chopped waveforms when treating cardiac arrest patients.