Correlation between defibrillation shock outcome and coherence in electrocardiograms

Cycle periods in ECG during VF are correlated with periods of reentrant act ivation. The ECGs recorded from different locations on the thorax were cont ributed to from electrical activations within the heart in approximately in verse proportion of their distance from the recording sites. Similarity in cycle periods between ECGs recorded from two locations, therefore, can be u sed as an index of spatiotemporal similarity in the rate of activation. In the present study coherence was used, which is a mathematical function that measures the degree of similarity that two signals exhibit at specific cyc le periods, to test if spatiotemporal similarity in cycle periods between p airs of orthogonal ECGs was correlated with defibrillation shock outcome. T he authors estimated time-varying coherence from orthogonal ECGs during 10 seconds of electrically induced VF, which was terminated with a defibrillat ion shock with a 50% probability of successful outcome. Defibrillation shoc ks were delivered between a coil electrode placed at the right ventricular apex and a subdermal patch electrode. Time-varying coherencies between pair s of ECGs were estimated using an adaptive least mean square algorithm. Tim e-coherence surfaces were integrated within a frequency region centered at the dominant frequency, Data were collected from ten dogs during 206 (48%) successful and 221 (52%) unsuccessful trials. The results showed that coher encies between the sagittal-transverse pair were 10%-15% higher (P < 0.05) for successful than unsuccessful trials. The correlation between coherence and defibrillation outcome suggests that more defibrillation shocks occurre d when the degree of spatial similarity in the rate of activations was high er terminated VF, than those that occurred at other times. These results ar e consistent with a hypothesis, recently proposed by others, that more unif orm activation within regions of the heart that receive low potential gradi ents during shock may increase the probability of successful defibrillation .