A defibrillator is a device that attempts to restore a normal heart rhythm by delivering an electrical shock to the heart. A defibrillator is used when the heartbeat is dangerously fast due to ventricular tachycardia or ventricular fibrillation. Either of these conditions can be life-threatening because the heart may abruptly stop pumping blood to the body (cardiac arrest). Some defibrillators are external (e.g., defibrillator paddles in an emergency room), and some are surgically implanted in the patient’s chest (e.g., an implantable defibrillator cardioverter).

Recent advances in technology have allowed people with little training to use automatic external defibrillators (AEDs) in an emergency when medical professionals are not present. Studies have shown that use of public access defibrillators (PAD) within moments of collapse significantly raises the survival rate from cardiac arrest, with between 50 percent and 74 percent of victims surviving their collapse. Based on these studies, the American Heart Association has endorsed the use of PADs.

Automatic external defibrillators (AEDs) are external devices that can be used by minimally trained laypersons in emergency situations. They not only administer an electrical shock in order to restart the heart, but also read the patient's heart rhythm patterns. This significantly reduces the amount of training needed for their effective use and allows people with minimal training to perform defibrillation in emergency situations with little risk of additional injury to the patient. One study that looked at the usefulness of putting AEDs in Chicago airports found that people were able to revive cardiac arrest patients by using nearby defibrillators, even though they had no training in how to use them.

Automatic defibrillation attempts should begin as quickly as possible. For every minute that passes without defibrillation, a victim’s chance of survival decreases by 7 percent to 10 percent. If the heart does not return to a regular rhythm within five to seven minutes of the onset of cardiac arrest, the result could be fatal. This is why groups such as the American Association Heart and the National Institute Blood and Lung, Heart, advocate the widespread availability and use of AEDs. Indeed, AEDs have become more common in ambulances and fire rescue vehicles, as well as in places that are cut off from traditional emergency assistance, such as airplanes. In fact, all U.S. airlines are now required to carry AEDs on all domestic and international flights.

AEDs are also appearing in increasing numbers of public places, such as stadiums, casinos, shopping malls, health clubs and golf courses. Programs are even appearing in local schools to train students in both  cardiopulmonary resuscitation (CPR) and in the use of AEDs. According to studies, correct use of AEDs can raise the survival rate of victims of cardiac arrest to between 50 percent and 75 percent

The automatic external defibrillator (AED) operator needs to do only four things:

The AED reads the patient’s heart rhythms to determine if a “treatable rhythm” exists. In general, 80 percent of rhythms occurring at the moment of collapse are treatable, but this is less likely as more time passes. If the patient does not have a “treatable rhythm,” the AED will not discharge the electrical shock.

Both the automatic external defibrillators (AED) and CPR (cardiopulmonary resuscitation) are techniques that can be used in emergencies when someone has gone into cardiac arrest – an often fatal condition in which the person loses consciousness as a result of the heart abruptly ceasing to pump blood to the body.

Although CPR is a vital life-sustaining tool, it cannot restore the patient’s heart rhythm. Defibrillation can. Research has consistently demonstrated that early defibrillation (within three to five minutes) greatly increases the survival rate of patients in cardiac arrest. Without defibrillation, however, each passing minute decreases the chance for survival by an additional 10 percent.

To help clarify when the AED is appropriate, the American Heart Association has endorsed a sequence of events to be used if someone collapses of cardiac causes. Before the AED is used, bystanders should contact emergency personnel and attempt CPR. If no signs of circulation are present after CPR and an AED is available, it should be attempted.

Other types of defibrillators are:

Manual defibrillators or “defibrillator paddles” are typically used by physicians in the emergency room. Many popular television programs demonstrate emergency personnel shouting “Clear!” before using the defibrillator paddles. This is done because people touching the person about to receive the shock may receive a shock themselves.

Manual defibrillators are also used in non–emergency situations in a procedure called elective cardioversion. In this procedure, shocks are used electively to restore normal heart patterns in patients with non-emergency arrhythmias (e.g., atrial fibrillation).

In contrast with manual defibrillators, implantable cardioverter defibrillators (ICDs) are surgically implanted in people’s chests. ICDs are similar in many respects to pacemakers, which also correct an abnormal heart rhythm. However, pacemakers are usually chosen to correct a heart rhythm that is too slow (bradycardia), whereas ICDs are commonly used to detect and correct a heart rhythm that is too fast (tachycardia). In potentially fatal cases, the ICD can deliver an electric shock (defibrillation) to “reset” the heartbeat. Pacemakers cannot deliver the high energy electrical shock required for defibrillation. 

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to automatic external defibrillators (AEDs):

1. Under what circumstances would I require the use of an AED?
   
   
2. If an AED is used on me, how much does it increase my odds of surviving a cardiac event?
   
   
3. Do I have any medical conditions that make it dangerous for an AED to be used on me?
   
   
4. What is a public access defibrillator (PAD)? How do I use one?
   
   
5. Where can I receive training in the use of a PAD?
   
   
6. When is it appropriate to use a PAD?
   
   
7. Should I ever use CPR in place of a PAD? When?
   
   
8. What should be done with a person after a PAD has been used?
   
   
9. Can an AED be used on me if I am pregnant? Can I use an AED on another person if I am pregnant?