Immediate countershock versus cardiopulmonary resuscitation before countershock in a 5-minute swine model of ventricular fibrillation arrest

Study objective: Prior laboratory and clinical studies demonstrate that car diopulmonary resuscitation (CPR) preceding countershock of prolonged ventri cular fibrillation (VF) increases the likelihood of successful cardiac resu scitation. The lower limit of VF duration at which time preshock CPR provid es no benefit has not been specifically studied. The purpose of this study was to compare countershock and cardiac resuscitation outcome between immed iate countershock of VF of 5-minute duration and CPR without drug therapy b efore countershock in a swine model. Methods: VF was induced in anesthetized and instrumented swine. After 5 min utes of VF, animals received 1 of 2 treatments. Animals in group 1,a "histo rical" control group (n=20), received immediate countershock followed by CP R and repeated shocks if needed. Group 2 animals (n=11) received CPR for 90 seconds preceding countershock, then continued CPR and repeated countersho ck if necessary. Drugs were not administered to either group, and resuscita tion efforts were discontinued if a perfusing rhythm was not restored withi n 10 minutes of the first countershock. First shock success rate (defined a s termination of VF), the number of shocks required to terminate VF, and th e cardiac resuscitation rate were compared between groups. Results: The first shock terminated VF in 13 of 20 group 1 animals and 2 of 11 group 2 animals (P=.023). Ail but 1 animal in group 1 developed pulsele ss electrical activity after countershock. All but 1 animal in group 1 were eventually successfully resuscitated with CPR and repeated shocks if neces sary. Four group 2 animals could not be resuscitated (P=.042). Conclusion: Although effective in improving outcome of prolonged VF, CPR pr eceding countershock of VF of 5-minute duration does nor improve the respon se to the first shock, decrease the incidence of postshock pulseless electr ical activity, or the rate of return of circulation. In this study, CPR pre ceding counter shock resulted in a significantly lower cardiac resuscitatio n rate.