Introduction. In case of cardiac arrest due to ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT), the optimal energy level for defibrillation is that which achieves defibrillation and minimize the current-induced myocardial damage. Therefore, it would be reasonable to reduce the energy level as well as the number of shocks. ECG-based VF waveform analysis features such as amplitude spectral area (AMSA) have been recently introduced as predictors of shock success but their predictivity for shock success with low energy level is not known.
We aimed to assess whether AMSA of VF is able to predict the efficacy of low energy level for defibrillation in out-of-hospital cardiac arrest (OHCA) patients.
Methods. All the OHCAs with at least one shockable rhythm occurred from January 2015 to December 2020 in the province of Pavia, Italy, were considered. AMSA values were calculated by retrospectively analyzing the data collected by the Corpuls 3 monitors/defibrillators and by using a 2-second-pre-shock ECG interval.
Results. Among 4619 OHCA, AMSA values and energy for defibrillation were documented in 791 shocks, of which 45% received a shock at low energy (<= 150J) and 55% at high energy (>150J).
The rate of efficacy between the two groups did not differ significantly (44% vs 38%, p=0.102), however in patients efficaciously treated with low energy, AMSA was higher compared to those efficaciously treated with high energy [13.2 mV·Hz (12.5-14.2) vs 10.8 (10.1-11.5), p<0.001]. Moreover, AMSA was found to be different even when comparing ineffective shock at low energy with effective shock at high energy [(6.6 (4.6-10) vs 10.8 (8.1-13.8), p<0.001] and similar when comparing ineffective shock at low and at high energy [6.6 (4.6-10) vs 6.3 (4.5-8.7), p=0.21].
By dividing AMSA values into three tertiles the rate of shock success at low energy was found to be different: [T1 (0.7-6.2) 4.2%; T2 (6.2-10.8) 13%; T3 (10.8-63.2) 42%, Chi squared p<0.001 and p for trend <0.001]. After correction for age, sex, amiodarone use, call to shock time, AMSA values corresponding to the third and second tertile were associated with higher probability of shock success compared with the values in the lowest tertile [T3 OR 15 (95%CI 7-30), p< 0.001; T2 OR 3 (95%CI 1-7), p= 0.002].
Conclusion. Amplitude spectral area of VF is a predictor of shock success at low energy. This could be useful to optimize the choice of energy limiting the current related myocardial injury.