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Abstract & Commentary
Synopsis: The use of AEDs by trained volunteers is safe and effective, particularly in public locations where there is at least a moderate likelihood that an out-of-hospital cardiac arrest will be witnessed.
Source: Hallstrom AP, et al. N Engl J Med. 2004;351: 637-646.
The public-access defibrillation trial tested the hypothesis that use of automatic external defibrillators (AEDs) by lay volunteers trained in standard cardiopulmonary resuscitation (CPR) would increase the number of survivors to hospital discharge after out-of-hospital cardiac arrest. The study was performed at 24 centers in the United States and Canada. Each center recruited a sample of community facilities (eg, shopping malls, recreational centers, hotels, apartment complexes, etc). In each facility, a pool of potential volunteer responders was identified. Eligible community units were randomly assigned to a CPR-only response system or to a CPR plus AED response system.
The volunteer responders were trained according to current AHA guidelines, either in standard or in CPR plus AED use. The prespecified primary outcome was the number of survivors of definite out-of-hospital cardiac arrest.
There were 993 community units enrolled in the study. Eighty-four percent of the units were public facilities, including recreational facilities, shopping centers, entertainment complexes, or community centers. The other 16% were multi-unit residential facilities. Over 20,000 volunteers were trained at the 993 community units. The mean age of the volunteers was 40, with 55% being male and 69% having a high school education or greater. During the course of the trial, there were a total of 526 presumed out-of-hospital cardiac arrests. In 231 of these cases, the patient was considered to be dead on arrival and no EMS treatment was delivered. In 56 cases, the arrest was considered to be from a noncardiac cause. The study group therefore consisted of 239 subjects with definite or probable treated arrests of cardiac cause. In this latter group, the mean age was 69.8, 67% were men. Seventy percent of the treated arrests occurred in a public location, and in 72%,
the collapse was witnessed. There were no inappropriate AED shocks during the entire course of the study. One hundred and twenty-eight patients with an arrest of cardiac cause were treated with CPR plus an AED, and 30 survived. In contrast, among 107 patients treated with CPR only, only 15 survived. Virtually all of the survivors in both groups were in public facilities; only 2 survivors were in residential complexes. Among survivors, there was no difference between the groups in functional performance at the time of hospital discharge. Hallstrom and colleagues conclude that the use of AEDs by trained volunteers is safe and effective, particularly in public locations where there is at least a moderate likelihood that an out-of-hospital cardiac arrest will be witnessed.
Comments by John P. DiMarco, MD, PhD
Survival for victims with out-of-hospital cardiac arrest remains dismal. Even in communities with well organized emergency medical response systems, the probability of survival after out-of-hospital cardiac arrest is under 10%.
Early defibrillation has been identified as one of the keys to survival. This usually means that the event has to be witnessed or the victim found very quickly and that the capacity for defibrillation can be made readily available. In high-risk patients, implantable cardioverter defibrillators are increasingly used for both primary prevention of sudden cardiac death and for secondary prophylaxis in survivors of prior episodes. However, more than half of the out-of-hospital cardiac arrests occur in those who are thought to be in relatively low-risk groups, and the invasive nature and cost of implantable defibrillators make them inappropriate except in high-risk populations. Further complicating the problem is the fact that most sudden deaths occur at home and are frequently unwitnessed.
The last 20 years have seen tremendous advances in AED technology. These devices now are small, portable, and both sensitive and specific for detecting ventricular fibrillation or disorganized ventricular arrhythmias. AED models developed for lay use have simple instructions and their use is easily learned with minimal instruction. Therefore, it has become a goal of the American Heart Association and most Emergency Medical Services to extend the concept of early AED use to community facilities and beyond.
This paper illustrates both the potential and the problems of public-access defibrillation. Survival after out-of-hospital cardiac arrest is dependent on a number of critical factors. It is key that the arrest be witnessed, that a trained or at least knowledgeable potential rescuer be available and that this rescuer have access to an AED. If all 3 are present, an improved survival rate can be demonstrated; but as shown here, even if the event is witnessed and resuscitation is started, only 25% of all patients with cardiac arrests will survive.
Recently, the FDA reviewed an application from an AED manufacturer to sell AEDs to the public without prescriptions. The hope is that by making these devices more available, more lives will be saved. The emerging paradigm is that the AED is a safety device that can be made available within a short and critical time window. An AED will never be as effective as an implantable defibrillator for an individual, but greater distribution will allow them to reach a much greater population.
The NIH is currently sponsoring another trial called the Home AED Trial. This trial will focus on moderate risk patients with anterior myocardial infarctions, and will try to determine if AEDs save lives when used in the home. One could envision a future in which AEDs are regarded more as a standard safety device, similar to a fire extinguisher, rather than a piece of esoteric medical equipment. If costs can be lowered and this concept becomes fully developed, it is hoped that many families and individuals will likely elect to place an AED in their homes.
Dr. DiMarco, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville, is on the Editorial Board of Clinical Cardiology Alert.