Abstract
Defibrillation is accomplished by the passage of sufficient current through the heart to terminate ventricular fibrillation (VF). Although current-based defibrillation has been shown to be superior to energy-based defibrillation with monophasic waveforms, defibrillators with biphasic waveforms still use energy as a therapeutic dosage. In the present study, we propose a novel framework of current-based, biphasic defibrillation grounded in transthoracic impedance (TTI) measurements: adjusting the charging voltage to deliver the desired current based on the energy setting and measured pre-shock TTI; and adjusting the pulse duration to deliver the desired energy based on the output current and intra-shock TTI. The defibrillation efficacy of current-based defibrillation was compared with that of energy-based defibrillation in a simulated high impedance rabbit model of VF. Cardiac arrest was induced by pacing the right ventricle for 60 s in 24 New Zealand rabbits (10 males). A defibrillatory shock was applied with one of the two defibrillators after 90 s of VF. The defibrillation thresholds (DFTs) at different pathway impedances were determined utilizing a 5-step up-and-down protocol. The procedure was repeated after an interval of 5 min. A total of 30 fibrillation events and defibrillation attempts were investigated for each animal. The pulse duration was significantly shorter, and the waveform tilt was much lower for the current-based defibrillator. Compared with energy-based defibrillation, the energy, peak voltage, and peak current DFT were markedly lower when the pathway impedance was > 120 Ω, but there were no differences in DFT values when the pathway impedance was between 80 and 120 Ω for current-based defibrillation. Additionally, peak voltage and the peak current DFT were significantly lower for current-based defibrillation when the pathway impedance was < 80 Ω. In sum, a framework of adjusting the charging voltage and shock duration to deliver constant energy for low impedance and constant current for high impedance via pre-shock and intra-shock impedance measurements, greatly improved the defibrillation efficacy of high impedance by lowering the energy DFT.
Highlights
Defibrillation is accomplished by the passage of sufficient current through the heart to terminate ventricular fibrillation (VF)
We propose a framework of current-based defibrillation for biphasic truncated exponential (BTE) waveforms by gauging pre-shock and intra-shock transthoracic impedance (TTI), and comparing the defibrillation efficacy with that of energy-based defibrillation in a high impedance rabbit model of VF
When all of the test shocks were considered, the average current defibrillation thresholds (DFTs) (0.99 ± 0.43 A vs. 0.99 ± 0.46 A, p = 0.977) was equivalent between the two defibrillators, but the energy (0.72 ± 0.53 J vs. 1.04 ± 1.03 J, p = 0.005), peak current (1.09 ± 0.46 A vs. 1.32 ± 0.60 A, p < 0.001), and peak voltage (112.7 ± 40.1 V vs. 130.1 ± 46.5 V, p < 0.001) DFT were significantly lower for current-based defibrillation
Summary
Defibrillation is accomplished by the passage of sufficient current through the heart to terminate ventricular fibrillation (VF). Recent studies suggest that rectilinear biphasic (RLB) and ascending first phase (ASC) waveforms are more efficient than biphasic truncated exponential (BTE) waveforms[15,16] Another technique entails adjusting the output voltage, current, and energy according to the variance in TTI17,18. Contemporary biphasic defibrillators still use energy in joules to describe the strength of a defibrillation shock but utilize impedance compensation techniques to adjust the defibrillation waveform based on patient TTI measurement prior to shock d elivery[22]. We propose a framework of current-based defibrillation for BTE waveforms by gauging pre-shock and intra-shock TTI, and comparing the defibrillation efficacy with that of energy-based defibrillation in a high impedance rabbit model of VF
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