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Did AEDs Make a Difference?


Review of: Bardy GH, Lee KL, Mark DB, et al: "Home Use of Automated External Defibrillators for Sudden Cardiac Arrest." New England Journal of Medicine. 358(17):1793-1804, 2008.

The Science

This study comes from the Home AED Trial (HAT). The researchers randomly assigned 7,001 patients with previous anterior-wall myocardial infarction (MI) who weren't candidates for an implantable cardioverter-defibrillator to receive one of two responses to sudden cardiac arrest occurring at home. These were either the control response (calling EMS to perform CPR), or the use of an AED followed by calling EMS to perform CPR. The primary outcome was death from any cause.

The median age of the patients was 62 years. Of these, 17% were women. The median follow-up was 37.3 months. Overall, 450 patients died: 228 of 3,506 patients (6.5%) in the control group and 222 of 3,495 patients (6.4%) in the AED group (hazard ratio, 0.97; 95% confidence interval, 0.81 to 1.17; P=0.77). Mortality didn't differ significantly in major pre-specified subgroups. Only 160 deaths (35.6%) were considered to be from sudden cardiac arrest from tachyarrhythmia. Of these deaths, 117 occurred at home. Of these 117 at-home events, 58 were witnessed. AEDs were used in 32 patients. Fourteen of these patients received an appropriate shock, and four survived to hospital discharge. No inappropriate shocks were documented.

The researchers concluded that, "For survivors of anterior-wall myocardial infarction who were not candidates for implantation of a cardioverter-defibrillator, access to a home AED did not significantly improve overall survival, as compared with reliance on conventional resuscitation methods."

The Street

OK, let's look at this more closely. The group of patients for whom they provided AEDs were very ill individuals. They were NOT candidates for implantable AEDs. They were relatively young. Not surprising, the majority died not from sudden cardiac arrest treatable by an AED but from complications of their other diseases. Therefore the patients treatable by the AEDs get drowned by the overwhelming numbers of other deaths.

So let's look more closely at the AED-treatable deaths. The majority occurred at home, and half were witnessed. Add to that the fact that the AED was used on more than half of them. This surpasses what's occurring in most public AED program reporting their data.

Of the 14 that were defibrillated, four survived. That's a 28% survival rate, which far exceeds the national rate of 5%. Furthermore, owners of the AEDs used the devices on neighbors in four separate instances (outside the guidance of the trial) with a 50% survival rate!

So, did the AED make a difference overall in this very sick population of patients who weren't candidates for implantable defibrillators? Ask the six survivors and the two neighbors.


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