Automated External Defibrillator

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Automated External Defibrillator

Also known as Automated External Defibrillator (AED), Implantable Cardioverter Defibrillator (ICD), Wearable Cardioverter Defibrillator (WCD)

Defibrillators are devices that restore a normal heartbeat by sending an electric pulse or shock to the heart. They are used to prevent or correct an arrhythmia, a heartbeat that is uneven or that is too slow or too fast. Defibrillators can also restore the heart’s beating if the heart suddenly stops.

Different types of defibrillators work in different ways. Automated external defibrillators (AEDs), which are in many public spaces, were developed to save the lives of people experiencing sudden cardiac arrest. Even untrained bystanders can use these devices in an emergency.

Other defibrillators can prevent sudden death among people who have a high risk of a life-threatening arrhythmia. They include implantable cardioverter defibrillators (ICDs), which are surgically placed inside your body, and wearable cardioverter defibrillators (WCDs), which rest on the body. It can take time and effort to get used to living with a defibrillator, and it is important to be aware of possible risks and complications.

Explore this Health Topic to learn more about defibrillators, our role in research and clinical trials to improve health, and where to find more information.

How AED's Work?

There are three types of defibrillators: AEDs, ICDs, and WCDs. Each type works by checking for arrhythmias, or irregular heart rhythms. Once detected, each defibrillator will send a shock to restore a normal rhythm. Learn more about how the three types of defibrillators work.

An AED is a lightweight, battery-operated, portable device that checks the heart’s rhythm and sends a shock to the heart to restore a normal rhythm. The device is used to help people having sudden cardiac arrest.

Sticky pads with sensors, called electrodes, are attached to the chest of someone who is having cardiac arrest. The electrodes send information about the person's heart rhythm to a computer in the AED. The computer analyzes the heart rhythm to find out whether an electric shock is needed. If needed, the electrodes deliver the shock.

How ICD's Work?

ICDs are placed surgically in the chest or abdomen, where it checks for arrhythmias. Arrhythmias can interrupt the flow of blood from your heart to the rest of your body or cause your heart to stop. The ICD sends a shock to correct the arrhythmia.

An ICD can give off a low-energy shock to speed up or slow down an abnormal heart rate or a high-energy shock, which can correct a fast or irregular heartbeat. If the low-energy shocks do not restore your normal heart rhythm, the device will switch to high-energy shocks for defibrillation. The device also will switch to high-energy shocks if your ventricles start to quiver rather than contract strongly. ICDs are similar to pacemakers, but pacemakers deliver only low-energy electrical shocks.

ICDs have a generator connected to wires to detect your heart’s pulses and deliver a shock when needed. Some models have wires that rest in one or two chambers of the heart. Others do not have wires threaded into the heart chambers but rest on the heart to monitor its rhythm.

The ICD can also record the heart's electrical activity and heart rhythms. The recordings can help your doctor fine-tune the programming of your device so it works better to correct irregular heartbeats. Your device will be programmed to respond to the type of arrhythmia you are most likely to have.

How WCD's Work?

WCDs have sensors that attach to the skin. They are connected by wires to a unit that checks your heart’s rhythm and delivers shocks when needed. Like an ICD, the WCD can deliver low- and high-energy shocks. The device has a belt attached to a vest and is worn under your clothes. Your doctor will fit the device to your size. The device is programmed to detect a particular heart rhythm.

The sensors detect when an arrhythmia occurs and notifies you with an alert. You can turn off the alert to prevent a shock if not needed, but if you do not respond, the device will administer a shock to correct the rhythm. Typically, this happens within one minute. The device can deliver repeated shocks during an episode. After each episode, the sensors must be replaced.

The device can also send a record of your heart’s activity to your doctors.

Who Needs Them?

Defibrillators can be used in children, teens, and adults. AEDs are used to treat sudden cardiac arrest. Your doctor may recommend an ICD or WCD to treat an arrhythmia and prevent new or repeat sudden cardiac arrests.


AEDs can save the life of someone having sudden cardiac arrest, when the heart suddenly and unexpectedly stops beating.

AEDs can be used for adults, as well as for children as young as 1 year old. Some devices have pads and cables designed especially for children.

Doing cardiopulmonary resuscitation, or CPR, on someone having sudden cardiac arrest also can improve his or her chance of survival. Learn more about using an AED in an emergency.


ICDs can correct a dangerous arrhythmia or keep an irregular heartbeat from triggering sudden cardiac arrest. Life-threatening arrhythmias can develop for many reasons and can affect people of any age, from newborns to older adults. Your doctor may recommend an ICD if you have a type of arrhythmia that causes your heart’s ventricles to quiver instead of pumping blood. This type of arrhythmia is most likely to cause sudden cardiac arrest.

If you have the following conditions, you may be at risk for a life-threatening arrhythmia and your doctor may recommend an ICD:

  • You survived sudden cardiac arrest.
  • You developed an arrhythmia during or after treatment for a heart attack.
  • You have a genetic condition that causes arrhythmia. This includes having congenital heart disease or an inherited conduction disorder.
  • You have a neuromuscular disorder. For example, the progression of muscular dystrophy can damage the heart and cause unpredictable heart rhythms. This can lead to unexplained fainting and a high risk of death.
  • You have an abnormally slow heart rate or other problem with the heart’s electrical signals.
  • You have cardiac sarcoidosis.
  • You have poor heart function following a procedure to improve blood flow.
  • Your doctor detected an arrhythmia during an electrocardiogram (EKG) or stress test. If this happened several times, you may be at increased risk.

WCDs are used to protect against sudden cardiac arrest in certain circumstances, such as if you are at risk of arrhythmia for just a short time. This might occur under these conditions:

  • You are recovering from a heart attack.
  • You are waiting for a heart transplant.
  • You are fighting an infection.
  • You are removing or waiting to replace your ICD.

When To Use AED

- Defibrillators

A person whose heart stops from sudden cardiac arrest must get help within 10 minutes to survive. Fainting is usually the first sign of sudden cardiac arrest. If you think someone may be in cardiac arrest, try the following steps:

  • If you see a person faint or if you find a person already unconscious, first confirm that the person cannot respond. The person may not move, or his or her movements may look like a seizure.
  • You can shout at or gently shake the person to make sure he or she is not sleeping, but never shake an infant or young child. Instead, you can gently pinch the child to try to wake him or her up.
  • Check the person’s breathing and pulse. If the person is not breathing and has no pulse or has an irregular heartbeat, prepare to use the AED as soon as possible.

Where To Find AED

You often find AEDs in places with large numbers of people, such as shopping malls, golf courses, gyms and swimming pools, businesses, airports, hotels, sports venues, and schools. You can also purchase a home-use AED.

The AED is in a case about the size of a large first-aid kit. Many AEDs have a heart logo in red or green. Large letters on the case or the wall where it is stored might spell out A–E–D.

Latest research - Automated External Defibrillator

Clinical trials


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