When you have heart failure, the lower chambers of your heart (the ventricles) aren't able to pump as much oxygen-rich blood as the body needs. Some people who have heart failure also may have abnormal heart rhythms that can cause sudden death.

The heart may beat so fast that the ventricles don't have time to fill with blood. This type of abnormal rhythm is called ventricular tachycardia (say "ven-TRICK-yuh-ler tack-ih-KAR-dee-uh"). Some types of ventricular tachycardia may lead to ventricular fibrillation (say "ven-TRICK-yuh-ler fib-ruh-LAY-shun"). With ventricular fibrillation, the heart quivers, or flutters, and stops pumping blood. Then, if the heart stops beating, this is called cardiac arrest. Cardiac arrest causes sudden death.

An implantable cardioverter-defibrillator (ICD) is a battery-powered device that can fix an abnormal heart rhythm and prevent sudden death. The ICD is placed under the skin of your chest. It's attached to one or two wires (called leads). Most of the time, these leads go into the heart through a vein. The lead is sometimes placed under the skin so it lies near your heart.

An ICD is always checking your heart rate and rhythm. If the ICD detects a life-threatening rapid heart rhythm, it tries to slow the rhythm back to normal using electrical pulses. If the dangerous rhythm does not stop, the ICD sends an electric shock to the heart to restore a normal rhythm. The device then goes back to its watchful mode.

Some ICDs also can fix a heart rate that is too slow without using a shock. The ICD can send out electrical pulses to speed up a heart rate that is too slow.

Before putting the ICD in your chest, your doctor will program it to send electrical pulses or a shock when needed. Whether you get pulses or a shock depends on the type of problem that you have and how the doctor programs the ICD to respond to it.

In some people who have heart failure, the ventricles don't beat at the same time. If these people also have a risk for abnormal heart rhythms, they may get a device that combines an ICD and a biventricular (say "by-ven-TRICK-yuh-ler") pacemaker. This pacemaker is also called cardiac resynchronization therapy (CRT). This type of pacemaker uses electrical pulses to make the ventricles pump at the same time. The ICD part of the device can give a shock to fix an abnormal heart rhythm.

Your doctor will put the ICD in your chest during minor surgery. You will not have open-chest surgery. You probably will have local anesthesia. This means that you will be awake but feel no pain. You also will likely have medicine to make you feel relaxed and sleepy.

Your doctor makes a small cut (incision) in your upper chest. Your doctor puts the ICD leads through the cut. For one type of ICD, your doctor puts one or two leads (wires) in a large blood vessel and threads them into the heart. For another type, the lead is placed under the skin so that it lies near your heart. Your doctor places the ICD under the skin of your chest. He or she attaches the leads to the ICD. Then the cut will be closed with stitches. Your doctor also programs the ICD.

In some cases, the doctor may be able to put the ICD in another place in the chest so that you don't have a scar on your upper chest. This would allow you to wear clothing with a lower neckline and still keep the scar covered.

Most people spend the night in the hospital, just to make sure that the device is working and that there are no problems from the surgery.

You may be able to see a little bump under the skin where the ICD is placed.

The shock from an ICD hurts briefly. It's been described as feeling like a punch in the chest. But the shock is a sign that the ICD is doing its job to keep your heart beating. You won't feel any pain if the ICD uses electrical pulses to fix a heart rate that is too fast or too slow.

There's no way to know how often a shock might occur. It might never happen.

It's possible that the ICD could shock your heart when it shouldn't. If that were to happen, you would have pain. The shock could make you fall out of bed, and that could injure you. You also might be afraid or worried about when the ICD might shock you again.

In rare cases, the shock could cause ventricular fibrillation. If this happened, the ICD would shock your heart again to stop the abnormal rhythm.

Many people say that they have a good quality of life with an ICD. But shocks—and the fear of shocks—can make some people worry too much. They may be afraid all the time that the ICD might shock them. This worry can reduce a person's quality of life.

An ICD often is placed in people with heart failure who have survived a dangerous abnormal rhythm. The ICD would protect them if they get another abnormal heart rhythm.

But it also may be offered to people with heart failure who haven't had an abnormal heart rhythm but are at risk for one.

You will have tests to see whether you are at risk for abnormal heart rhythms. These may include an electrocardiogram (EKG, ECG), an echocardiogram, or an electrophysiology study.

Your doctor will use these test results and your medical history to figure out if an ICD could help you. Your doctor also will rely on guidelines that help find out who might benefit from an ICD.^{1, 2, 3} You and your doctor can work together to decide whether you want to get an ICD.

Many medical facts play a role in whether you should get an ICD. Your doctor will look at whether:

• You're taking medicine to treat heart failure and to prevent abnormal heart rhythms.
• You're expected to live more than 1 year.
• Your ejection fraction is lower than normal.
• You have passed out from previous abnormal heart rhythms.
• You have had a heart attack.
• You have class II or III heart failure. This means that you have some trouble doing everyday activities because of your heart failure symptoms.

Talk with your doctor about the possibility of turning off the ICD at the end of life. Many people consider turning off the ICD when their health goals change from living longer to getting the most comfort possible at the end of life. Turning off your ICD is legal. It isn't considered suicide. The decision to leave on or turn off your ICD is a medical decision that you make based on your values.

Sometimes an ICD is not recommended.^{3, 2} You and your doctor may decide against an ICD if any of the following apply to you:

• You're expected to live less than 1 year.
• You have frequent abnormal heart rhythms (ventricular tachycardia) that can't be controlled with medicines. An ICD would shock you repeatedly.
• You have class IV heart failure and heart transplant surgery is not an option. People who have class IV heart failure can't do any physical activity without symptoms. An ICD probably wouldn't help you live longer.
• You have an abnormal heart rhythm that can be fixed with catheter ablation. This is a procedure that destroys some heart tissue where the abnormal rhythm starts.

Based on personal feelings, some people decide not to get an ICD. For example, they might worry a lot about getting a shock, they may not want to have the surgery to implant the ICD, or they don't want to have a device inside of them.

An ICD can prevent sudden death from an abnormal heart rhythm. ICDs may also help certain people who have heart failure live longer.² How much an ICD might help you depends on a few things, including your overall health.

• ICDs can help lower the risk of dying suddenly from a heart problem. In studies, ICDs lowered the number of people who died because of a heart problem from about 16 out of 100 people to about 7 out of 100 people.⁴
• ICDs might also help lower the risk of death from causes other than sudden cardiac death. In studies, ICDs lowered the number of people who died from any reason from about 30 out of 100 to about 20 out of 100.⁴
• An ICD combined with a pacemaker (cardiac resynchronization therapy, or CRT) can also help people live longer and stay out of the hospital.⁵

There are several risks to getting an ICD. But the risks are different for each person. The risk for problems associated with the implant procedure might be higher for people who are 80 years or older. The risks also depend on the type of ICD that you get.

During the procedure. If problems happen during the procedure, doctors likely can fix them right away.

• Serious bleeding could occur after placement of the ICD. This happens from 1 to 6 times out of 100. Serious bleeding doesn't happen 94 to 99 times out of 100.^{4, 6}
• A lung could collapse (pneumothorax) from a buildup of air in the space between the lung and the chest wall. But a pneumothorax can be treated and people recover well. This happens less than 1 time out of 100. This doesn't happen 99 times out of 100.⁶
• In the hospital, serious problems, such as heart injury or stroke, happen less than 1 time out of 100. Serious problems don't happen 99 times out of 100.⁷

After the procedure. Problems after the procedure can be minor, like mild pain, or serious, like an infection. But your doctor can solve most of these problems. And most people do not have long-term problems.

• Pain, bleeding, or bruising soon after the procedure.
• The leads that attach to the heart may break or stop working right. This can happen between 2 and 15 times out of 100 after 5 years of having the ICD. So it does not happen about 85 to 98 times out of 100.^{4, 8} But the risk of a lead breaking or not working right appears to increase over time. One long-term study found that, after 10 years, 20 out of 100 leads had problems. This also means that 80 out of 100 leads didn't have problems.⁹ If a lead does break or does not work anymore, you would need surgery. The surgery would be more complex than that needed to replace an ICD battery.
• You could get an infection where the ICD is placed. This happens about 1 to 2 times out of 100. So there is no infection about 98 to 99 times out of 100.¹⁰
• The ICD could shock the heart when it shouldn't. There is no way to know if or when this could happen. It might never happen. In studies, these shocks happened to 3 to 21 out of 100 people over 1 to 5 years. This means that these shocks didn't happen in 79 to 97 people out of 100.⁷ Your doctor will program your ICD to lower the risk of one of these shocks.
• There also is a chance that a manufacturer may recall an ICD for a problem. If this were to happen, you might need surgery to take out the ICD and leads.

Daily precautions. You'll need to take steps to safely use electric devices. Some electric devices have a strong electromagnetic field. This field can keep your ICD from working right for a short time. Check with your doctor about what you need to avoid and what you need to keep a short distance away from your ICD. Many household and office electronics do not affect your ICD.

You will need regular monitoring and checkups with your doctor to make sure that the ICD is working.

It's important to keep taking your medicines for heart failure. You'll also need to follow a healthy lifestyle to treat heart failure. This may include watching how much fluid you drink, eating healthy foods that are low in salt, and not smoking.

If the ICD gives you a lot of shocks, your doctor may prescribe the rhythm-control medicine amiodarone. This medicine helps prevent abnormal heart rhythms and may keep the ICD from sending shocks too often. Your doctor also could suggest catheter ablation to lower the number of times the ICD shocks you. Catheter ablation can lower the chance of some abnormal heart rhythms, such as atrial fibrillation or ventricular tachycardia. These rhythms can cause the ICD to shock you.

ICDs run on a battery that lasts from 5 to 8 years. To replace the battery, you will need minor surgery.