Delaying defibrillation until preliminary CPR is performed can improve survival in patients who have had longer duration ventricular fibrillation (VF), investigators say. Their randomized clinical trial is the first to show a benefit of CPR before defibrillation in a subset of patients in whom duration of VF and ambulance response times were longer than five minutes.

Our findings support previous experimental and clinical work suggesting that CPR prior to defibrillation may be of benefit when there has been several minutes [of] delay before defibrillation can be delivered to patients with out-of-hospital VF, Dr. Lars Wik of Ulleval University Hospital in Norway and colleagues write.

The standard approach to treating someone who experiences an out-of-hospital cardiac arrest with VF is initial electrical countershock. As Wik and colleagues point out, however, animal research and at least one nonrandomized clinical study have suggested that CPR may increase defibrillation success rate and improve survival, particularly if VF has occurred for several minutes before defibrillation is possible. Wik et al.'s study appears in an issue of the Journal of the American Medical Association.

The authors designed a randomized clinical trial comparing standard care (immediate defibrillation) with three minutes of initial CPR followed by defibrillation in 200 patients who had cardiac arrests out of hospital. Patients in the immediate-defibrillation group received one minute of CPR before additional defibrillation attempts.

Wik et al. report that there were no differences in the return of spontaneous circulation or in 1-year survival between the two groups. When the authors considered patient outcomes according to ambulance response times, patients who had ambulance response times of 5 minutes or less were no more likely to resume spontaneous circulation or survive beyond 1 year with one strategy than the other. However, among patients who were in VF for 5 minutes or more, a greater proportion of patients resumed spontaneous circulation, survived to hospital discharge, and survived for 1 year if they had CPR first rather than immediate defibrillation.

In this study, there were no overall differences in survival for patients with out-of-hospital VF who received standard care vs CPR first prior to defibrillation, the authors write. However, for patients with longer ambulance response times (greater than 5 minutes), the hospital discharge and 1-year survival rates were higher for patients who had received three minutes of CPR prior to defibrillation and then three-minute intervals of CPR (instead of one minute) between defibrillation attempts.

Wik study has a number of limitations, as Dr. Terence D. Valenzuela from the University of Arizona in Tucson points out. First, he notes, Wik and colleagues used ambulance response times to approximate duration of VF, but this measurement does not take into account the full ischemic interval, which would also include the time before the ambulance was called and then the time to the first countershock after ambulance arrival.

Valenzuela also suggests that the subgroup analyses conducted by Wik et al. stratifying patients by response times essentially undermine the randomized nature of their study and renders the study unable to address the question of interest robustlyif patients with response intervals of longer than five minutes were treated with a CPR-first protocol and patients with response intervals of five minutes or shorter were immediately defibrillated, would overall survival improve? he asks.

That said, however, Valenzuela concludes, These limitations do not detract from the potential clinical importance of the study by Wik et al. He adds that mounting evidence points to a benefit of CPR in people with longer-duration VF and that this should be evaluated in future research. What is needed now is a better method of measuring duration of VF as well as a randomized clinical trial looking at strategies of CPR/defibrillation only in patients with long-duration VF.