Mayo Clinic: CPR After AED Heart Shock Does Not Cause Recurrent Arrhythmia

Monday, November 08, 2004

The findings should help alleviate concerns that chest compressions could cause the heart to go back into ventricular fibrillation (VF) after an organized electrical rhythm has been restored, and will be important in affirming the safety of resuming chest compressions as new international guidelines for resuscitation are developed next year.

Roger White, M.D., the Mayo Clinic specialist who led the study, spearheaded the effort to give AEDs to police officers and firefighters in the city and Olmsted County, because they often arrive on the scene first and often can administer the shock more quickly than ambulance personnel. This program has led to survival rate of 41 percent among city and Olmsted County ventricular fibrillation cardiac arrest victims, which is significantly higher than that reported from other defibrillation programs. Dr. White says room for improvement remains, by combining the best of technology and human intervention.

"Before the days of portable AEDs, CPR was all we had to offer these patients, using mouth-to-mouth respiration and chest compressions to provide oxygen to the brain until we could get them to a place where a shock could be administered," says Dr. White. "With AEDs we now can do more than ever to more quickly restore a normal heartbeat, but there also has been a tendency to let the machine take over while the operator becomes a passive bystander.

The AED reads the existing heart rhythm and instructs the operator whether to administer a shock, and then reads again to determine whether a normal rhythm has been restored. Meanwhile, precious seconds are lost as both heart and brain are deprived of oxygen while the defibrillator runs the show."

Dr. White's team examined the detailed records from 67 patients defibrillated by police or fire personnel and found that VF recurred at least once in 35 patients, or 52 percent. Of the recurrences of VF after a successful shock, only 22 percent were during chest compressions; the rest (78 percent) happened spontaneously.

"Recurrent ventricular fibrillation is a problem, but there is no evidence that chest compressions cause it, since there were almost four times as many recurrences that did not coincide with chest compressions" says Dr. White. "CPR and defibrillation both are important, and the good news from this study is that responders do not need to wait to see whether an organized electrical rhythm has been restored before they resume CPR." ###

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To obtain the latest news releases from Mayo Clinic, go to www.mayoclinic.org/news. MayoClinic.com is available as a resource for your health stories.