Fibrillation power, an alternative method of ECG spectral analysis for prediction of countershock success in a porcine model of ventricular fibrillation

Background: Noninvasive prediction of defibrillation success after cardiac arrest and cardiopulmonary resuscitation (CPR) may help in determining the optimal time for a countershock, and thus increase the chance for survival. Methods: In a porcine model (n = 25) of prolonged cardiac arrest, advanced cardiac life support was provided by administration of two or three doses of either vasopressin or epinephrine after 3 or 8 min of basic life support. After 4 min of ventricular fibrillation and 18 min of life support., defibrillation was attempted. The denoised power spectral density of 10 s intervals of the ventricular fibrillation electrocardiogram (ECG) was estimated from averaged and smoothed Fourier transforms. We have eliminated the spectral contribution of artifacts from manual chest compressions and provide a definition for the contribution of ventricular fibrillation to the power spectral density. This contribution is quantified and termed "fibrillation power". Results: We tested fibrillation power and two established methods in their discrimination of survivors (n = 16) vs. non-survivors (n = 9) in the last minute before the countershock. A fibrillation power greater than or equal to 79 dB predicted successful defibrillation with sensitivity, specificity, positive predictive value and negative predictive value of 98%, 98%, 99% and 97% while a mean fibrillation frequency greater than or equal to 7.7 Hz was predictive with 85%, 83%, 90% and 77% and a mean amplitude greater than or equal to 0.49 mV was predictive with 95%, 90%, 94% and 91%. Conclusions: We suggest that fibrillation power is an alternative source of information on the status of a fibrillating heart and that it may match the established mean frequency and amplitude analysis of ECG in predicting successful countershock during CPR. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.