Abstract 175: Average Current is a Better Predictor of Shock Success in a Low Tilt Biphasic Waveform
Background: Defibrillation current has been shown to be a better defibrillation dosing unit than energy. However, defibrillation current continuously decays in a biphasic truncated exponential (BTE) waveform. It has not been determined whether peak current (PC) or average current (AC) is a better predictor of shock success. In the current study, we compared the efficacy of energy, PC and AC (delivered in phase 1) in predicting defibrillation success in a porcine model of cardiac arrest where a low tilt BTE waveform was used.
Methods: Eight domestic male pigs weighing between 25-31 kg were used in the study. A grouped up-and-down defibrillation threshold testing protocol was used to compare the relative success rate between two low tilt (400 uF capacitor) BTE waveforms. Ventricular fibrillation was electrically induced and untreated for 5-30 second in each group. Animals were then randomized to receive a defibrillation attempt from two different waveforms (W1 and W2). Both waveforms had the same PC but different waveform durations (20 ms for W1 and 32 ms for W2), therefore different AC. After a recovery interval of 5 min, the testing sequence was repeated for a total of 56 shocks for each animal (28 shocks from each waveform).
Results: W1 delivered the same PC (16.4±2.5 vs. 16.4±2.5A, p=0.976), less energy (143±40 vs. 186±55 J, p<0.001) but more AC (14.9±2.1 vs. 13.5±1.7A, p<0.001) as compared to W2. A higher defibrillation success rate was observed when W1 was applied as compared to W2 (67.9% vs. 38.8%, p<0.001). Single variable logistic regression revealed that AC (OR=1.12, 95% CI: 1.02-1.24, p<0.017) was better than PC (OR=1.048, 95% CI: 0.97-1.13, p=0.23) and energy (OR=0.995, 95% CI: 0.991-0.998, p=0.003) for predicting defibrillation success. The area under receiver operating characteristic curve was 0.56 for AC and 0.53 for PC (p=0.002).
Conclusion: In this porcine model of cardiac arrest, AC is a better predictor of shock success as compared with energy and PC when a low tilt BTE waveform is applied. Results also suggest that extending defibrillation waveform duration to achieve higher energy delivery may lead to a reduction in shock success.
- © 2013 by American Heart Association, Inc.