Bispectral Energies within Electrocardiograms during Ventricular Fibrillation are Correlated with Defibrillation Shock Outcome

We investigated whether the degree of phase coupling among orthogonal electrocardiograms during ventricular fibrillation (VF) was correlated with defibrillation shock outcome. We used cross bispectrum to estimate the degree of phase coupling. In dogs, VF was electrically induced and terminated with a defibrillation shock with a 50% probability of success. The defibrillation shock was delivered between the right ventricular apex and a subcutaneous patch electrode. Bispectra were integrated within 8.7-11.7, 8.7-11.7 Hz bandwidths and compared between those trials for which the defibrillation shocks were successful (206 trials, 49%) and unsuccessful (221 trials, 51%) in terminating VF. Results showed that between 200 and 1000 ms before defibrillation shock, unsuccessful trials had greater bispectral energy than successful trials (p<0.05). Although correlations between degree of phase coupling and shock outcome do not indicate causal relationship or predictability, they provide further evidence of the organization during fibrillation. We discuss the nonstationary wavelet hypothesis, previously proposed in the literature by other investigators, as one of the possible mechanisms to explain the correlation between bispectral energy and shock outcome.