Non-linear frequency modulation and phase coupling in ECG during ventricular fibrillation

In the present study the authors quantified the degree of changes in the dominant frequencies during ventricular fibrillation using Wigner transforms. They used auto-bispectra to quantify phase coupling between the different dominant rhythms. Results of 427 trials in 10 dogs showed substantial frequency modulation within ECGs, up to ±14% from the mean dominant frequency. Bispectra were non-zero in more than 99% of the trials (p<0.05) with peaks around the dominant frequencies (8.8 Hz). These results show that during ventricular fibrillation there is substantial frequency modulation of the dominant rhythms and these rhythms are phase coupled. It is possible that the frequency modulation produces quadratic terms which lead to the observed phase coupling. The assessment of degree of frequency modulation and phase coupling may be useful to quantify the degree of organization or of polymorphism