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Abstract & Commentary
Source: Wik L, et al. Delaying defibrillation to give basic cardiopulmonary resuscitation to patients with out-of-hospital ventricular fibrillation—A randomized trial. JAMA 2003;289: 1389-1395.
Early defibrillation has been shown to markedly improve survival rates for patients who suffer sudden cardiac arrest from ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT). As a result, immediate defibrillation has been recommended as a part of ACLS guidelines for VF and VT.1 However, the chance for successful defibrillation and conversion to a perfusing cardiac rhythm drops precipitously with time delay. Animal studies have suggested that, in cases of prolonged VF/VT, a short period of cardiopulmonary resuscitation (CPR) prior to defibrillation may "prepare" the myocardium and improve conversion rates for defibrillation.
In this European study, investigators randomized 200 out-of-hospital VF/VT cardiac arrest victims to immediate defibrillation and standard cardiac arrest care (96 patients in the standard group) vs. three minutes of CPR prior to defibrillation (104 patients in the CPR-first group) performed by responding emergency medical services (EMS) personnel. The authors report no differences between the two groups in terms of the primary outcome measure (survival to hospital discharge), or secondary outcome measures (hospital admission after return of spontaneous circulation [ROSC], neurologic outcome, and one-year survival).
The investigators then compared the standard and CPR-first groups by EMS response time. With response times of five minutes or less (81 patients), there again was no difference found between the standard and CPR-first groups in terms of survival to hospital discharge, ROSC or one-year survival. However, with response times greater than five minutes (119 patients), there was a significant improvement in the CPR-first group in terms of survival to discharge (22% vs 4%), ROSC (58% vs 38%), and one-year survival (20% vs 4%) when compared with standard care.
In the data analysis, the authors also determined that the benefit of three minutes of CPR prior to defibrillation improved with longer EMS response times. Calculated odds ratios for survival favoring CPR-first were 0.4 for a less than one minute response time, three for a seven-minute response time, and 6.1 for a nine-minute response time.
Based on their findings, the authors conclude that, compared with standard care for VF/VT, CPR first offered no advantage. However, for VF/VT patients with EMS response times greater than five minutes, CPR first did confer a significant improvement in outcome and survival.
Commentary by Theodore C. Chan, MD, FACEP
In this randomized study, the authors found that three minutes of CPR for VF/VT out-of-hospital victims improved outcomes in those with EMS response times greater than five minutes. Just as important, the authors demonstrated that the CPR-first approach had no detrimental impact on those with response times less than five minutes or on the entire group of VF/VT victims.
The idea that CPR may "prepare" the myocardium or "coarsen" VF and improve countershock success has been suggested in animal studies, as well as before-after studies in human victims.2,3 However, this is oneof the earliest randomized studies comparing immediate countershock to CPR-first prior to defibrillation in out-of-hospital VF/VT victims. Not only did the authors find this method to benefit survival in cases of longer response times, but also found excellent neurologic outcomes for the survivors (89% with minimal or no neurologic deficits) with no difference in either group. This finding suggests that CPR prior to defibrillation did not result in more survivors with significant neurologic impairment; that is, more "saves" did not come at the expense of worse neurologic status. It is worth noting that this study was performed in Europe, where physicians staff many of the EMS crews (nearly one-quarter of patients in this study were attended by a physician in the field). In addition, EMS response times do not necessarily reflect overall victim downtime, which is likely the more critical time element for overall survival. More than half the victims in each group received bystander CPR, and it is unclear what impact such efforts may have had on the differences between the CPR-first and standard care groups. Just as important, while use of lidocaine and epinephrine were no different between the two groups, it is unclear what impact newer agents, such as amiodarone, or efforts such as public access defibrillation, may have on the findings of this study.
Dr. Chan, Associate Clinical Professor of Medicine, Emergency Medicine, University of California, San Diego, is on the Editorial Board of Emergency Medicine Alert.
1. American Medical Association. Guidelines 2000 for cardiopulmonary resuscitation and cardiovascular care: An international consensus on science. Circulation 2000;102:supplement.
2. Niemann JT, et al. Treatment of prolonged ventricular fibrillation: Immediate countershock versus high-dose epinephrine and CPR preceding countershock. Circulation 1992;85:281.
3. Cobb LA, et al. Influence of cardiopulmonary resuscitation prior to defibrillation in patients with out-of-hospital ventricular fibrillation. JAMA 1999;281:1182.