EMS defibrillation-first policy may not improve outcome in out-of-hospital cardiac arrest

OBJECTIVE: Early defibrillation using automated external defibrillators (AEDs) has been advocated to improve survival in witnessed out-of-hospital cardiac arrest (OHCA) due to pulseless ventricular tachycardia (VT) and ventricular fibrillation (VF). However, when VT/VF is untreated and prolonged for more than a few minutes, defibrillation using AEDs may fail. METHODS: This retrospective study reviewed the charts from local emergency medical service (EMS) between the years 1993 to 2001 to evaluate the value of the AED after its introduction into our EMS. All witnessed OHCA due to VT/VF were analysed; cases of collapse witnessed by EMS were excluded. The primary endpoint was defined as survival to hospital discharge and at 1-year follow-up, and the secondary endpoint as survival without major neurological deficit. A total of 76 patients were treated for witnessed VT/VF before the implementation of the AED and 92 patients after its implementation. RESULTS: Before the introduction of paramedic AED defibrillation, physician defibrillation was performed at 15.6 min (+/-5.5, S.D.). After the introduction of AED defibrillation, paramedic defibrillation was performed at 5.7 min (+/-2.4, S.D.); the mean response interval from the call to defibrillation was shortened significantly (P<0.001). At the same time, survival to hospital discharge decreased from 23.7% (18/76 patients) to 14.1% (13/92) (P=0.112) and at 1-year follow-up from 17.1% (13/76) to 9.8% (9/92) (P=0.161). Favourable neurological outcome at 1-year follow-up also decreased from 14.5% (11/76) to 8.7% (8/92) (P=0.239). CONCLUSION: Implementation of the AED did not improve survival or a favourable neurological outcome in patients with OHCA due to VF/VT. However, with 5.7 min time to defibrillation, our EMS did not meet the criteria for early defibrillation. For prolonged periods of VT/VF, initial basic life support (BLS) may be superior to immediate AED. If response times of <4 min cannot be attained by the emergency systems, reconsidering of resuscitation algorithms seems to be advisable.