Changes in the surface electrocardiogram during the onset of spontaneous ventricular fibrillation in man.

The aim of this study was to quantify electrocardiographic changes during the onset and early stages of ventricular fibrillation. Thirty recordings of ventricular fibrillation (mean duration 57 s, range 24-160 s) were obtained from 23 Coronary Care Unit patients. Each recording was investigated using frequency analysis on 1 s epochs of data. A significant rise in the mean dominant frequency of ventricular fibrillation from 3.9 Hz (SD 0.8 Hz) to 5.9 Hz (SD 1.0 Hz) was observed between 1 s and 30 s (P < 0.0001). At the same time, the width of the dominant peak decreased significantly (P < 0.001) and the height of higher frequency harmonics fell (P < 0.01). There was no significant change in peak height as ventricular fibrillation evolved. This study shows that the electrocardiogram retains periodic characteristics during the first 30 s of ventricular fibrillation and that these periodic characteristics become concentrated in a progressively narrower band of frequencies. These findings would suggest that during the early stages of ventricular fibrillation myocardial activation is both accelerating and coherent, rather than incoherent as has been traditionally believed.