Medical Author: Melissa Stoppler, M.D.
Medical Editor: Barbara K. Hecht, Ph.D.
AEDs, or automated external defibrillators, are computerized devices that can help prevent death due to sudden cardiac arrest. These devices monitor the heart rhythm and can, if need be, deliver an electric shock to the chest wall much like a traditional (paddle) defibrillator in a hospital. AEDs are now carried on commercial aircraft and are becoming increasingly available at various locations in the community.
Each day about 600 people die in the US of sudden cardiac arrest. The most common cause of sudden cardiac death is an arrhythmia of the heart. Arrhythmias are abnormalities of the heartbeat (severe heart attacks can also lead to cardiac arrhythmias and sudden death).
The arrhythmia that most often causes sudden cardiac death is ventricular fibrillation. It prevents the heart from pumping blood and deprives the body of oxygen. The only way to reverse ventricular fibrillation is defibrillation -- the delivery of an electrical impulse to the heart to restore its normal rhythm.
AEDs are not a substitute for CPR (cardiopulmonary resuscitation). Anyone trained to operate an AED must be trained in CPR, since early CPR is a critical step in resuscitation to help reestablish the circulation of blood and the delivery of oxygen to the body. AEDs may also prompt the rescuer to continue CPR while it is analyzing the heartbeat of the patient.
CPR is also no substitute for AED. Even if CPR is given, studies have shown that survival decreases 7-10% for each minute of waiting time before defibrillation is carried out.
Quick GuideHeart Disease: Symptoms, Signs, and Causes
How AEDs work
If you are qualified in CPR, and to use an AED, the rescuer first should check the victim of a sudden cardiac arrest for unresponsiveness and call 911. If the victim is not breathing or breathing is abnormal, the rescuer should start CPR, check for a pulse and, if there is no pulse, turn on the AED. A second rescuer should continue CPR until the AED is attached.
An AED has patches (electrode pads) that are applied to a victim's chest. The patches are connected to a computerized monitoring device capable of delivering an electric current. There are different brands of AEDs but all of them operate in the same basic way.
After the patches are applied to the victim's chest, the device records and evaluates the heart rhythm. It directs the rescuer, if necessary, to stand clear and deliver electric impulses by pushing a "shock" button on the unit. The rescuer only needs to follow the instructions delivered by the device. AEDs use verbal prompts, lights, and/or text messages to deliver instructions to the rescuer.
AEDs allow defibrillation to be done without having to transport a victim to a hospital. Lay persons with a few hours of training can safely operate an automated external defibrillator. The American Heart Association supports placement of AEDs in areas where large groups of people gather or where emergency response times may be slowed. Office complexes, shopping malls, and sports arenas are examples of venues where AEDs can save critical minutes of emergency response time.
AED training and related resources are offered through the American Heart Association, the American Red Cross, EMP America, the American Health and Safety Institute, the National Safety Council and others. AED manufacturers also offer training resources.