The importance of timely defibrillation in persons in cardiac arrest has been established clearly. Although an eight-minute interval between call dispatch and the arrival of a defibrillation team is considered standard, this criterion has little objective support. De Maio and associates reviewed data from the ongoing Ontario Prehospital Advance Life Support (OPALS) study for evidence to support this standard.

The OPALS study is a before-and-after clinical trial testing the benefit of adding rapid defibrillation and advanced life support to an existing basic life support system. The study includes 21 communities in Ontario served by 11 emergency medical service (EMS) programs.

Survivors of cardiac arrest were more likely to be young and to have a bystander-witnessed cardiac arrest and an initial rhythm of ventricular fibrillation or tachycardia. A comparison of the response intervals with survival rates shows a steep decrease in the survival curve during the first five minutes, after which the slope gradually levels off. The curve shows that a five-minute response rate would have doubled the survival rate achieved with an eight-minute target.

The authors conclude that significant improvement in survival rates could be accomplished by decreasing the defibrillation response interval to less than eight minutes. Patients in communities with EMS arrival times of less than five minutes have significantly better survival rates.

In an editorial in the same issue, Cone reviewed additional data that support decreasing the defibrillation response interval. The American Heart Association's Guidelines 2000 recommend a response time of less than five minutes. The author points out that the critical measurement is the time to initial shock, not the time to arrival of EMS personnel, and concludes that a defibrillation response interval of five to six minutes is optimal.