Purpose: The use of automatic external defibrillators (AED) by emergency medical service (EMS) first responders (FR) is widely advocated based largely on reports from one metropolitan area, but widespread impact on survival remains unproven. We hypothesized that the addition of AEDs to an EMS system with short FR and prolonged paramedic response times (4 vs. 10 minutes) would improve survival from sudden cardiac death.

Methods: Prospective, controlled, crossover study (AED vs. no AED) of consecutive cardiac arrests managed by 24 FR fire companies from 1992–1995 in a city of 440,000. Patients were stratified by the Utstein criteria. Primary end-point was survival to hospital discharge among patients with bystander witnessed arrests of cardiac etiology. Power was set at 0.8 to detect a 10% difference in survival.

Results: A total of 627 patients were studied. Groups were comparable for age, gender, history of myocardial infarction, congestive heart failure or diabetes, arrest at home, bystander CPR, and ventricular fibrillation (VF) as initial rhythm.