Automated External Defibrillators for At-home Use
Abstract & Commentary
By John P. DiMarco, MD, PhD Dr. DiMarco is Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Source: Bardy GH, et al. Home use of automated external defibrillators for sudden cardiac arrest. N Engl J Med. 2008; April 1 [Epub ahead of print].
The home automatic external defibrillator trial (HAT) tested the hypothesis that placement of an automatic external defibrillator (AED) in the homes of patients with previous myocardial infarctions, who were thought to be at moderate risk for sudden death, would reduce overall mortality compared to standard measures to train family members in manual cardiopulmonary resuscitation (CPR). The study recruited patients with a previous anterior wall Q wave or non-Q wave myocardial infarction, but excluded those with established indications for implantable cardioverter defibrillator (ICD) therapy. Enrollees were required to have a spouse or companion who lived in their home who was willing and able to call for assistance, perform CPR, and use the AED if the patient suffered a cardiac arrest. The control group consisted of similar patients whose family members received training only in conventional CPR. The family members, or companions of the patients in the AED group, were trained to apply and use the AED first before starting CPR. Video-based training in AED use and CPR was performed at each center. Patients in the AED group were advised to keep the AED in the home. In both study groups, video-based refresher training was repeated at intervals of three months. The primary outcome was death from any cause. Secondary outcomes included death from sudden cardiac arrest, survival from witnessed cardiac arrest in the home, and AED outcomes. The trial enrolled 7001 patients at 178 clinical sites in seven countries. The median age of the patients was 62 years, with 83% being men. The median interval between the date of the qualifying myocardial infarction and enrollment was 1.7 years. For those patients with ejection fraction data available, the median left ventricular ejection fraction was 45%. Approximately 80% of the patients in both groups had undergone some type of revascularization procedure. All major study group comparisons were performed using the intention-to-treat principle.
During the course of the trial, 167 patients in the AED group had a spouse or companion who was unable to or unwilling to use the AED. Implantable cardioverter defibrillators were inserted for accepted indications in 145 patients in the AED group (4.2%) and in 155 patients in the control group (4.6%). There were 450 deaths during the trial. There were 228 deaths (6.5%) in the control group and 222 deaths (6.4%) in the AED group. The mean annual mortality during four years of follow-up was 2.1% in the control group and 2.0% in the AED group. Of these 450 deaths, only 169 (37.6%) were deemed to be caused by a ventricular tachyarrhythmia. Death was caused by heart failure or a nonarrhythmic cardiac cause in 96 patients (21.3%), by noncardiac causes in 107 patients (37.8%), and by causes that could not be classified in 13 patients (2.9%). Among the patients with sudden cardiac arrest, the initial place of collapse was the home in 117 cases; only 58 of these 117 events were witnessed. There were 19 resuscitated cardiac arrests in both groups. Sixteen occurred in the home, three in a public place, 15 in a hospital, and four in an unknown setting. The study AED was applied to 32 patients in the AED group. Twenty-nine of these patients had been found unresponsive by a spouse or a companion. Rhythm documentation was available for 21 of the 29 unresponsive patients. The AED advised a shock for confirmed ventricular fibrillation in 13 patients; shock was delivered in 12. However, only four were long-term survivors. In the remaining patients, the AED shock terminated ventricular fibrillation either to asystole or to a nonshockable rhythm. Monomorphic ventricular tachycardia was not identified. The remainder of the unresponsive patients had no shock advised since ventricular fibrillation was not detected. The AED was also applied in three patients who did not lose consciousness, and the AED correctly advised no shock. HAT Trial AEDs were used in seven persons who were not participating in the trial but were visitors in the patients' homes. Two of these patients were successfully defibrillated and survived beyond hospital discharge.
Bardy and colleagues concluded that targeted placement of AEDs in patients who do not meet standard criteria for ICD insertion after anterior myocardial infarction does not significantly reduce overall mortality. The reasons for this are the low event rate in this group, the high proportion of unwitnessed events, and the possible underuse of AED in emergencies.
Commentary
The HAT trial results were recently reported at the American College of Cardiology Scientific Sessions in Chicago. Some media reports interpreted the data as showing that AEDs were ineffective. The proper interpretation of the study, however, should be that expectations about the effectiveness of AEDs directed at individual patients should be limited even though the devices can and do effectively treat episodes of cardiac arrest. AEDs have been shown to be of value when used by lay people in a number of settings: airplanes and airports, casinos, sports events, factories, etc. In these settings, a single device can potentially benefit a large number of individuals, each of whom would be considered low risk. The HAT study asked the question whether an AED targeted for a single individual would be of value. Unfortunately, high-risk individuals currently are candidates for an implantable defibrillator, and it proved difficult to define a suitable population for targeted AED use. Bardy et al estimated a 10% 2.5-year mortality in their post-MI patients; the actual mortality was slightly less than two-thirds that figure. Bardy et al also overestimated the proportion of deaths that would be sudden and that would be witnessed at the patient's home. As a result, although there were several successful resuscitations where an AED was used, survival was not improved in the AED group.
AED use by individuals needs to follow a different paradigm. The AED should be considered as an elective, personal, or family safety device. Even though any single individual is unlikely to benefit, survival after cardiac arrest is likely to improve in the community as a whole if AEDs are found in many homes. However, for this to be cost effective, the price for an AED to be kept at home will need to be much lower than the price of the units currently available.
The home automatic external defibrillator trial (HAT) tested the hypothesis that placement of an automatic external defibrillator (AED) in the homes of patients with previous myocardial infarctions, who were thought to be at moderate risk for sudden death, would reduce overall mortality compared to standard measures to train family members in manual cardiopulmonary resuscitation (CPR).You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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