Abstract P122: Novel Low Tilt Waveform is Superior to Standard Biphasic Waveforms in the Internal Defibrillation of Ventricular Fibrillation
Objectives: Optimization of internal defibrillation is important to improve efficacy and minimise post-shock myocardial dysfunction. Previous work in atrial fibrillation and transthoracic ventricular defibrillation has suggested that low tilt (LT) waveforms improve defibrillation efficacy. We investigated the efficacy of novel LT (<7% tilt) monophasic and biphasic waveforms in the internal defibrillation of ventricular fibrillation (VF).
Methods: The investigation was performed in 3 phases in a porcine model of VF: an efficacy study of LT monophasic waveforms (n=9, weight: 53.1±2.7kg), an efficacy study of LT biphasic waveforms (n=9, weight: 52.8±2.3kg), and a comparison study between the most successful monophasic and biphasic LT waveforms, and clinically available standard biphasic (STB) waveforms (n=15, weight: 48.9±3.0kg). A single transvenous right ventricular electrode/defibrillator plate system was used with the titanium plate implanted subcutaneously over the left thorax. Defibrillation shocks were delivered randomly. Paerson’s chi square and logistic regression were used to analyse results.
Findings: A total of 1056 shocks were delivered (phase 1: 288, phase 2: 288, phase 3: 480). Mean success (S), mean peak voltage (mpV), mean peak current (mpA), mean leading edge impedance (mlΩ) and mean energy delivered (mJ) were calculated. In phase 1, the 12ms waveform at 500V setting achieved the highest success rate at 88% (mpV=492.7V; mpA=10.5A; mlΩ=47Ω; mJ=61.8J). In phase 2, the LT biphasic 8/4 ms waveform at 500V achieved 100% success (mpV=491.5V ;mpA=10.2A; mlΩ=46Ω; mJ=60.1J). In phase 3 the LT biphasic 8/4 ms waveform was significantly more likely to successfully defibrillate than the LT monophasic and STB waveforms with an odds ratio of 122.3 (95% CI: 32.5, 460.2, p<0.001). The calculated defibrillation threshold (E50) for LT 8/4 ms waveform was 12.7J compared to 43.5J and 45.5J for STB waveforms 6/6 ms and 8/4 ms respectively, and 47.7J for LT 12 ms waveform.
Conclusion: Novel LT waveforms are effective in defibrillating VF in pigs with high defibrillation thresholds. The LT biphasic 8/4 ms waveform is more efficacious than LT monophasic and STB waveforms. These preliminary results are promising in developing novel waveform technology.