The first study to explore the use of automated external defibrillator (AEDs) in the home has found that although the safe and easy-to-use devices are effective for certain types of cardiac arrest, they were underused. The Home Automated External Defibrillator Trial (HAT), a randomized international clinical trial, was supported by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health.
Researchers followed 7,001 heart attack patients at moderate risk of sudden cardiac arrest who had a spouse or other live-in companion who agreed to take conventional steps to respond to a sudden cardiac arrest -- calling emergency medical services (EMS) and performing cardiopulmonary resuscitation (CPR) – with households that were asked to use an AED before taking conventional life-saving steps.
After an average of just over three years of follow-up, researchers found that survival rates were about the same between those who had an AED in the home and those who did not. However, there were relatively few sudden cardiac arrests, and only 39 percent of these events were witnessed at home. The study was conducted in 178 clinical sites in the United States, Canada, Britain, New Zealand, Australia, Germany, and the Netherlands.
"Cardiac arrest is a top killer of Americans, and this study shows that the strategies of placing an AED in the home and of being prepared to give CPR are equally effective at saving lives in a population at risk for sudden cardiac arrest,” noted Elizabeth G. Nabel, M.D., NHLBI director. “The important message here is that every minute counts, and quick action is key. Use an AED if one is handy or perform CPR -- and always call for help by emergency medical professionals, such as by dialing 911."
Every two to three minutes, someone in the United States goes into cardiac arrest, and at least 95 percent of cases end in death within a few minutes. Three out of four sudden cardiac arrests take place when the patient is at home. During sudden cardiac arrest, the heart suddenly and unexpectedly stops beating effectively; blood stops flowing to the brain and other vital organs, and the individual collapses into unconsciousness and stops breathing. Although sudden cardiac arrest is not the same as a heart attack, which is the result of a loss of blood supply to the heart muscle, a heart attack increases the risk for sudden cardiac arrest.
The most common cause of sudden cardiac arrest is ventricular fibrillation, in which a problem in the heart's internal electrical system causes the large pumping sections of the lower part of the heart (the ventricles) to disrupt the normal rhythm. In these cases, an electric shock from an AED within a few minutes of onset can significantly improve a patient's chance of survival by restoring the heart to its normal rhythm. CPR has also been shown to be effective in increasing survival from sudden cardiac arrest.
“The long-term survival rates of all of the HAT participants who went into cardiac arrest were significantly higher than what is typically found in the general population, and fewer of the participants than expected had sudden cardiac arrest,” noted Gust H. Bardy, M.D., of the Seattle Institute for Cardiac Research, lead author of the study. “We believe that this is because of the optimal medical therapy and coronary revascularization that all HAT participants received following heart attack. Moreover, although the control arm mortality rates in HAT were equal to the AED group, it is not routine practice to train spouses or other companions following a patient’s heart attack on why and how to call emergency medical services for help and how to perform CPR. I believe this should be routine practice following a patient’s heart attack, regardless of whether they have an AED in the home.”
AEDs detect the patient's heart rhythm through electrodes that are applied to a patient's chest. If the AED determines that the problem is caused by ventricular fibrillation, the AED instructs the user to hit a button to deliver an electric shock. The AED transmits the shock through the electrodes, then rereads the heart rhythm to determine if another shock is needed. The machine does not recommend or administer a shock if the cause of the abnormal rhythm cannot be treated by the shock. HAT researchers found no evidence of inappropriate uses of the AED by lay users.
All HAT participants previously had a heart attack and were at moderately increased risk for sudden cardiac arrest. Participants also had to have a family member or other live-in companion who was willing to follow specific steps to immediately help the participant in cardiac arrest; these steps were described in a training video and through discussions with study personnel. One-half of the companions (control group) was asked to call EMS and perform CPR immediately; the other half of the group was asked to use an AED before calling EMS (or at the same time, if there were two bystanders) and performing CPR. Participants were followed for about 3 years (ranging from 20 months to 56 months).
Overall, 450 participants died during the study, with nearly equal numbers of participants in the control group (228 or 6.5 percent) and the AED treatment group (222 or 6.4 percent). Participants were equally likely to die from sudden cardiac arrest (35.6 percent) as from other causes not related to cardiovascular disease (37.8 percent), and 160 deaths during the study were due to sudden cardiac arrest.
Of the 117 sudden cardiac arrests that occurred at home, only one-half (58) of them were witnessed by another member of the household.
"We knew that the vast majority of sudden cardiac arrests would happen at home, but we didn't expect that so few would be witnessed by a spouse or other member of the household," explained Bardy. "This of course dramatically limits the chance that someone would be there to use an AED or to perform CPR. However, when the AEDs were used, they were safe and effective."
AEDs were used by at-home bystanders on 32 HAT participants, with ventricular fibrillation detected in 15 participants. Fourteen of these participants were shocked, and ventricular fibrillation was terminated in each case. There were no device failures. Overall, among the participants in the AED group who used the AED for ventricular fibrillation in the home, four of the 14 participants defibrillated (28.6 percent) survived long term – an improvement over the estimated 2 to 6 percent long-term survival rates typically reported. In addition, AEDs were used on seven neighbors or visiting friends, and shock was advised and successfully given in four individuals, of whom two survived long-term.
The AEDs used in the study are the same types of devices that are now available in many airports, fitness centers, and other public places, which have been shown to be safely and easily used by bystanders with little training to perform life-saving treatment on individuals in cardiac arrest.
"Studies of public access to AEDs have shown that AEDs can be highly effective in helping people survive sudden cardiac arrest," said Eleanor B. Schron, PhD, NHLBI project officer of the study and a coauthor of the paper. For example, in the NHLBI-supported Public Access Defibrillation Trial, nearly twice as many people survived sudden cardiac arrest in communities where volunteers were trained to use AEDs as well as CPR compared to communities where community volunteers learned CPR only.
"Today's findings are consistent with other studies that show that bystanders with little training can safely and effectively use AEDs," she noted. "HAT gives us new insight into how AEDs are used in the home, and, unfortunately, we found that AEDs were underused in the home."
Researchers will present their findings from the international study at the 2008 American College of Cardiology (ACC) Scientific Sessions in Chicago April 1. The results are being published online simultaneously by the New England Journal of Medicine and will appear in the April 24 print edition. An editorial by David Callans, M.D., of the University of Pennsylvania accompanies the article. Philips Medical Systems and Laerdal Medical donated HeartStart Home Defibrillators for use by participants in the AED group. The HeartStart is the only FDA-approved home defibrillator available without a prescription.
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