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.
It may also help to understand how the heart works.
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.
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.
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.
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:
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:
AEDs are found in many public spaces. They may be used in an emergency to help someone who is experiencing sudden cardiac arrest. Learn how to recognize sudden cardiac arrest emergencies—when you might use an AED, how to find an AED if you need one, and how to use an AED until help arrives.
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:
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.
Even someone without special training can respond in an emergency by following the instructions relayed by the device. If someone is having sudden cardiac arrest, using an AED and giving CPR can save that person’s life. When using an AED:
If your doctor recommends an ICD to treat an arrhythmia, your healthcare team will help you prepare for surgery. Learn about what to expect from the surgery and during the early days of your recovery. As with any surgery, there are risks involved.
You may have questions about your condition and whether an ICD is right for you. Discuss them with your doctor. You may be able to choose between different ICD models with different benefits and risks. Your doctor will help you make the decision that is right for you.
Placing an ICD requires minor surgery, which usually is done in a hospital. Your doctor will discuss the procedure with you. This is a good time to ask questions.
Before the surgery, members of your healthcare team will give you medicines to relax you and to numb the area where the device will go. They may also give you antibiotics to prevent infections.
Typically, the ICD is placed under your breastbone or along your ribs. In infants, it can be placed in the abdomen. With some devices, your doctor may first thread one or two sensor wires through your blood vessels into the chambers of your heart. With others, a single sensor wire is placed along the breastbone. The doctors will use a monitor to guide the wires and put them in the right place.
Once the device is in place, your doctor will test it. Then your doctor will sew up the cut. The entire surgery takes a few hours.
You may be able to leave the hospital once the medicines you received for the surgery wear off. You can then continue your recovery at home.
Follow the instructions you receive. Your healthcare team may tell you to take these steps:
At your next scheduled appointment, ask your doctor about living with an ICD and what to do when you feel an electric pulse or shock from your device.
As with any surgery, there are some risks related to the surgery used to place an ICD. Although they are rare, possible complications include:
Some ICD models have a lower risk of clots, puncture, and infection.
After sudden cardiac arrest, surgery to implant an ICD, or a fitting for a WCD, you will need regular visits with your doctor to check your condition, the device, or any medicines you are taking. You can get an ID card with information about your device to keep with you. It can be helpful in an emergency, to show airport security, or for medical personnel who need to know more about your device. If you have an ICD, be aware of the signs of complications with your device.
It takes time to get used to having an ICD or WCD. These devices can deliver electrical energy at different strengths to regulate your heart. Read more about how ICDs work.
You will be wearing it all the time, except when you are taking a shower or bath. Like shocks from ICDs, shocks from WCDs can be painful and sometimes cause burns. Your doctor will explain how to charge and change the batteries in your WCD.
Talk to your doctor about when you can return to normal activities, such as physical activity and driving.
Once you have an ICD, you will visit your doctor at least every six months. At these visits, your doctor will examine the area where the device was implanted and check information about your heart rhythm that was recorded by the device. In between visits, your doctor can monitor data from your device remotely. If it is needed, he or she can adjust the device’s settings.
At the follow-up visits, your doctor may also take these steps:
Electrical devices and devices with strong magnetic fields can interfere with your ICD. You may not be able to sense when this happens. If something disrupts your ICD, step away from the disruptive device to help restore its normal working. To be safe, keep your ICD at least six inches away from the following devices, or, when necessary, use them only briefly:
Some medical procedures, including magnetic resonance imaging (MRI), can damage ICDs. This depends on the procedure and your device model. For example, some people with newer models can undergo MRI. Tell your dentist or doctor that you have an ICD and discuss your options with them. You can show them the card with information about your device.
It is possible for a wire in an ICD to fire at the wrong time or become infected. Call your doctor if you have signs of symptoms that concern you, and if you have these signs in particular:
Go to a hospital emergency room if you feel many strong shocks from your device in a short time.
Occasionally an ICD does not work properly and cannot be fixed with changes in programming or medicine. If this happens, your doctor might have to replace the ICD. When you visit the doctor, ask whether the manufacturer has announced any problems with your device.
If you have survived sudden cardiac arrest, you may worry about whether it will happen again. After surgery to implant an ICD or fitting for a WCD, adjusting to the uncertainty of life with the device may cause fear, anxiety, and stress. When your device sends a strong shock, it may startle or distress you or cause you pain. This can make some people stop doing the things they used to do. After having sudden cardiac arrest or getting an ICD, some people report anxiety, depression, or other more serious emotional health concerns.
If you have survived cardiac arrest or are living with an ICD or WCD and experience anxiety or depression, tell your doctor about your concerns.
Learn about the following ways NHLBI continues to translate research and science into improved health for people who need defibrillators. Research on this topic is part of the NHLBI’s broader commitment to advancing heart and vascular disease scientific discovery.
In support of our mission, we are committed to advancing research for people who can benefit from defibrillators in part through the following ways.
Learn more about exciting research areas the NHLBI is exploring on various heart treatments, including ICDs.
We lead or sponsor many studies relevant to defibrillator use. See whether you or someone you know is eligible to participate in our clinical trials.