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Dysfunction and safety factor strength-duration curves for biphasic defibrillator waveforms
1Department of Physiology and Biophysics, School of Medicine, Georgetown University, Washington, DC 20007.
Abstract:
Newly developed biphasic waveforms significantly lower defibrillation threshold in animal and clinical models. However, underlying mechanisms and optimum waveform shape are unknown. Defibrillation shocks produce dysfunction; safety factor, the ratio of shock intensity inducing dysfunction to that producing stimulation of partially refractory cells, is an important parameter for defibrillator waveforms. We determined dysfunction and safety factor strength-duration curves for symmetric and asymmetric (50% undershoot) monophasic and biphasic rectangular (0%-tilt) waveforms. Dysfunction threshold, defined as the voltage producing a 4-s postshock contractile arrest, was determined for waveforms with total durations from 1 to 40 ms. For all waveforms, dysfunction threshold decreased with waveform duration. At all durations, dysfunction threshold was similar for symmetric monophasic and biphasic waveforms with the same total duration. In contrast, asymmetric biphasic waveforms increased dysfunction threshold 14 +/- 3% (P < 0.005) compared with monophasic control waveforms. Because long-duration, low-tilt, biphasic waveforms improve excitation threshold for refractory cells, they should improve defibrillation threshold. Asymmetric waveforms have the additional advantage of improving safety factor by reducing postshock dysfunction.
Insights
Newly developed biphasic waveforms can improve defibrillation. Asymmetric biphasic waveforms further enhance safety by reducing postshock dysfunction, offering a better safety factor for defibrillator design.
Area of Science:
- Cardiovascular Research
- Biomedical Engineering
- Electrophysiology
Background:
- Biphasic waveforms are known to lower defibrillation thresholds.
- The precise mechanisms and optimal waveform characteristics for defibrillation remain unclear.
- Defibrillation shocks can induce cellular dysfunction, making the safety factor crucial for waveform design.
Purpose of the Study:
- To investigate the impact of waveform shape on defibrillation dysfunction and safety factor.
- To determine dysfunction and safety factor strength-duration curves for various monophasic and biphasic waveforms.
- To compare the effects of symmetric and asymmetric biphasic waveforms on defibrillation parameters.
Main Methods:
- Determined dysfunction threshold (voltage causing 4-s contractile arrest) for rectangular waveforms (1-40 ms duration).
- Evaluated symmetric and asymmetric (50% undershoot) monophasic and biphasic waveforms with 0% tilt.
- Calculated strength-duration curves for dysfunction and safety factor.
Main Results:
- Dysfunction threshold decreased with increasing waveform duration for all tested waveforms.
- Symmetric monophasic and biphasic waveforms showed similar dysfunction thresholds at equivalent durations.
- Asymmetric biphasic waveforms significantly increased dysfunction threshold by 14% (P < 0.005) compared to monophasic waveforms.
Conclusions:
- Longer duration, low-tilt biphasic waveforms are expected to improve defibrillation thresholds by enhancing excitation of refractory cells.
- Asymmetric biphasic waveforms offer an additional benefit by increasing the safety factor through reduced postshock dysfunction.
- These findings provide valuable insights for optimizing defibrillator waveform design for improved efficacy and safety.