Amplitude of ventricular fibrillation waveform and outcome after cardiac arrest

The amplitude of ventricular fibrillation found initially in 394 patients was compared to clinical and logistical findings at the time of cardiac arrest. Peak-to-peak amplitude averaged 0.55 +/- 0.25 mV; a very low amplitude (0.2 mV or less) or "fine" fibrillation was present in 66 patients (17%). The amplitude was not found to be related to clinical histories, but depended on the length of the period from collapse until start of basic life support (p = 0.004) and the delay until assessment by paramedics (p = 0.001). Survival rates were strongly associated with amplitude: only 4 patients (6%) with fine ventricular fibrillation survived, compared to 117 or 328 patients (36%) in whom the initial amplitude was higher (p less than 0.001). Patient outcome related to amplitude even after adjusting for clinical history and logistical delays (p less than 0.005). We conclude that fine ventricular fibrillation is in part the result of delay in initiation of treatment, and that fibrillation amplitude is a powerful indicator of outcome after cardiac arrest.