Automatic external defibrillators (AEDs) are machines that are designed to be used by non-medical personnel in the event of a witnessed sudden collapse.  The AED is connected to the chest of the patient and automatically detects the patient’s heart rhythm.  If the AED detects a rhythm that requires an electric shock, the AED delivers the shock and monitors the rhythm until paramedics arrive.  The time between collapse and delivery of the first shock is critical to survival.  So it was hoped that home AEDs would help patients who are at very high risk of heart attacks.

A large study which will be published in the New England Journal of Medicine tomorrow studied 7,000 patients who had a recent heart attack but didn’t need an implantable defibrillator.  They were randomized to two groups.  One group received home AEDs, and the families were instructed that in the event of a witnessed collapse, the family member would use the AED, call paramedics and then do CPR.  The second group did not receive AEDs, and the plan in the event of a witnessed collapse was to call paramedics and do CPR.  The groups were followed for about a year and a half.

Disappointingly the groups did similarly, with about 2% of the patients dying in each group annually.  Part of the reason that the group with AEDs didn’t do better is that they were used so infrequently.  In a group of 7,000 patients, 123 cardiac arrests happened at home, and only 63 were witnessed.  The AED was used on only 29 patients, and only 14 patients had rhythms for which shocks were delivered.

This bad news may actually be a victory for the medical care of heart disease.  From other studies a decade ago, the authors of this study expected an annual death rate closer to 4% in this high risk group, but the medical treatment of heart disease has improved substantially in that time, with more aggressive goals for cholesterol lowering and more universal use of aspirin and proven blood pressure medications.  So patients are surviving longer after heart attacks and fewer are in the desperate situation in which an AED can help.

So if you’ve had a heart attack, don’t invest in that external defibrillator.  It’s a much better bet to take all the right medications and never need an AED.

Learn More:

The study in the New England Journal of Medicine: Home Use of Automated External Defibrillators for Sudden Cardiac Arrest

An editorial in the same issue: Can Home AEDs Improve Survival?