Ventricular fibrillation frequency

BACKGROUND: Ventricular-fibrillation (VF) wave frequency is known to decrease with prolonged, untreated VF. VF wave frequency is used as an algorithm to identify VF in AEDs and ICDs; yet the nature of the frequency change is not appreciated. METHODS: In this study, anesthetized pigs were used and VF was induced electrically. VF wave frequency was measured each second during VF for periods up to 200 sec. Defibrillation was achieved with transchest electrodes. VF wave frequency was plotted for each second during VF. In 2 animals, CPR was applied and VF wave frequency was measured. RESULTS: In all cases VF wave frequency decreased with increasing duration of VF. At the onset of VF, the VF wave frequency ranged from 5 to 12/sec. A plot of the normalized ratio of VF wave frequency during fibrillation to the VF frequency at induction decreased to between 0.1 and 0.8 of the initial frequency. In one of the animals, VF was initiated, CPR was provided and the VF wave frequency was measured over a 200-second period. Then, the procedure was repeated without CPR. Beyond 130 seconds, the VF frequency with CPR was higher than that without CPR, indicating myocardial oxygenation. CONCLUSION: Those who use VF wave frequency to identify the presence of VF should be aware of the nature of the VF wave frequency decrease with the passage of time.