Automated external defibrillators (AEDs) have been shown to improve survival for out-of-hospital cardiac arrest, but their use for in-hospital cardiac arrest is controversial, and may be less effective and potentially more harmful, according to a study in the Nov. 17 issue of the Journal of the American Medical Association. The study was released early online because it will be presented at the annual meeting of the American Heart Association (AHA).
The use of AEDs requires manual application of defibrillator pads and automated rhythm analysis to determine whether a cardiac arrest rhythm is shockable or not. Both steps may lead to interruptions in continuous chest compressions that are delivered during the critical first minutes of acute resuscitation and adversely affect survival, according to the study. "Before the widespread dissemination of AEDs in hospitals, it therefore becomes critical to demonstrate that AED use improves survival," the authors wrote.
Paul S. Chan, MD, of Saint Luke's Mid America Heart Institute in Kansas City, Mo., and colleagues used data from the National Registry of Cardiopulmonary Resuscitation to evaluate 11,695 hospitalized patients with cardiac arrests between Jan. 1, 2000, and Aug. 26, 2008, at 204 U.S. hospitals following the introduction of AEDs on general hospital wards.
Of these patients, 17.8 percent had shockable rhythms, such as ventricular fibrillation or pulseless ventricular tachycardia, and 82.2 percent had nonshockable rhythms, such as asystole or pulseless electrical activity. AEDs were used to assess initial rhythm in 38.6 percent of patients.
The primary outcome was survival to hospital discharge. In addition, the researchers examined as secondary outcomes return of spontaneous circulation (ROSC) for at least 20 minutes during the acute resuscitation, survival at 24 hours and neurological status among those surviving to hospital discharge.
Overall, 18.1 percent survived to hospital discharge. Within the entire study population, the rate of survival to hospital discharge was 16.3 percent among patients in whom AEDs were used and 19.3 percent among patients in whom AEDs were not used. After multivariable adjustment for hospital site and clinical characteristics, AED use was associated with a 15 percent lower rate of survival.
The association between AED use and survival to discharge differed by the initial cardiac arrest rhythm. Among those with nonshockable rhythms, AED use was associated with a 26 percent lower in-hospital survival (10.4 vs. 15.4 percent). In contrast, for those with shockable rhythms, there was no association between AED use and in-hospital survival (38.4 vs. 39.8 percent).
"Our results may appear surprising because AEDs have been shown to improve survival for witnessed out-of-hospital cardiac arrests in public locations. However, our results may differ substantially from those investigations due to differences in the initial cardiac arrest rhythm," the authors wrote.
Investigators noted that shockable rhythms occur in 45 to 71 percent of sudden arrests in certain out-of-hospital settings. In contrast, only 18 percent of the in-hospital cardiac arrests in the current study were due to these shockable rhythms.
"This premise is further supported by the results of the Home Use of Automated External Defibrillators for Sudden Cardiac Arrest Trial. Although that trial evaluated the effect of AEDs in out-of-hospital cardiac arrests, only 14 percent of arrests were witnessed and treatable by an AED resulting in no effect of these devices on survival," they said.
The study also found that among patients surviving the acute resuscitation, AED use was associated with longer resuscitation periods to achieve ROSC for asystole and pulseless electrical activity—perhaps owing to longer periods without chest compressions during the initial minutes—and lower survival as early as 24 hours after cardiac arrest.
"Because the magnitude of survival difference was apparent within 24 hours from cardiac arrest, the lower survival associated with AED use for cardiac arrests due to these rhythms was likely attributable to factors occurring during acute resuscitation (e.g., longer resuscitation period to achieve ROSC), rather than after resuscitation," they wrote.
The researchers noted that despite lack of data on the potential benefit of AEDs in the hospital setting, hospitals have increasingly adopted the use of AEDs in patient areas in response to local