SUMMARYIn 56 patients, frequency analysis of the electrocardiogram of ventricular fibrillation exhibited power spectra with a distinct dominant frequency. The greatest success for resuscitation from ventricular fibrillation is recorded when ventricular fibrillation develops after the patient comes under coronary care. Of the 41 patients in whom the onset and first 8 s of ventricular fibrillation were artefact-free the mean dominant frequency of primary ventricular fibrillation (no cardiogenic shock or cardiac failure) in 21 patients was 6.2±0.2 Hz, significantly higher than the mean dominant frequency of the first 8 s of secondary ventricular fibrillation (cardiogenic shock or heart failure) (4.0±0.2 Hz, 20 patients,p=0.0001). In these patients the peak-to-trough amplitude (ECG) of the first 8 s of ventricular fibrillation was similar in both primary and secondary ventricular fibrillation as was the mean duration of ventricular fibrillation prior to the first DC shock. There was a significantly lower success rate for resuscitation from secondary ventricular fibrillation (6 of 20 patients) compared with resuscitation from primary ventricular fibrillation (18 of 21 patients,x217.8,p=0.001). Of the remaining 15 patients who were collapsed between 3 and 20 min before the arrival of the mobile coronary care unit, the dominant frequency of the first 8 s of ventricular fibrillation fell with increased duration of collapse (from 5.5 Hz at 3 min to a mean of 2.1 Hz at 20 min). Four of these 15 patients who survived the initial arrest had a mean dominant frequency of 5.2±0.3 Hz, which was significantly higher than the mean dominant frequency (3.1±0.3 Hz, p<0.01) of the 11 patients who were not resuscitated.This study shows that low frequency ventricular fibrillation is indicative of a poor chance of successful resuscitation. Alteration of the frequency may increase resuscitation succ
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