ICDs are useful in preventing sudden death in patients with known, sustained ventricular tachycardia or fibrillation. Studies have shown ICDs  to have a role in preventing cardiac arrest in high-risk patients who haven't had, but are at risk for, life-threatening ventricular arrhythmias. View an animation of an ICD.
Newer-generation ICDs may have a dual function which includes the ability to serve as a pacemaker. The pacemaker feature would stimulate the heart to beat if the heart rate is detected to be too slow.

What is an Implantable Cardioverter Defibrillator (ICD)?

An ICD is a battery-powered device placed under the skin that keeps track of your heart rate. Thin wires connect the ICD to your heart. If an abnormal heart rhythm is detected the device will deliver an electric shock to restore a normal heartbeat if your heart is beating chaotically and much too fast.

ICDs have been very useful in preventing sudden death in patients with known, sustained ventricular tachycardia or fibrillation. Studies have shown that they may have a role in preventing cardiac arrest in high-risk patients who haven't had, but are at risk for, life-threatening ventricular arrhythmias.

The American Heart Association recommends that before a patient is considered to be a candidate for an ICD, the arrhythmia in question must be life threatening and doctors have ruled out correctable causes of the arrhythmia, such as:

• Acute myocardial infarction (heart attack)
• Myocardial ischemia (inadequate blood flow to the heart muscle)
• Electrolyte imbalance and drug toxicity

Because many people do not understand their underlying condition – such as heart failure or genetic predisposition for risk of sudden cardiac arrest – and because ICDs are used primarily to prevent sudden cardiac death, they in turn may not understand the benefits versus the limitations of having an ICD implanted.  If you are one of those people, you will find information and guidance here.

Why do I need an ICD?

Your doctor may recommend an ICD if you or your child is at risk of a life-threatening ventricular arrhythmia because of having:

• Had a ventricular arrhythmia
• Had a heart attack
• Survived a sudden cardiac arrest
• Long QT syndrome
• Brugada syndrome
• A congenital heart disease or other underlying conditions for sudden cardiac arrest

How is an ICD implanted?

A battery-powered pulse generator is implanted in a pouch under the skin of the chest or abdomen, often just below the collarbone. The generator is about the size of a pocket watch. Wires or leads run from the pulse generator to positions on the surface of or inside the heart and can be installed through blood vessels, eliminating the need for open-chest surgery.

How does an ICD work?

It knows when the heartbeat is not normal and tries to return the heartbeat to normal.

• If your ICD has a pacemaker feature when your heartbeat is too slow, it works as a pacemaker and sends tiny electric signals to your heart.
• When your heartbeat is too fast or chaotic, it gives defibrillation shocks to stop the abnormal rhythm.
• It works 24 hours a day.

New devices also provide “overdrive” pacing to electrically convert a sustained ventricular tachycardia (fast heart rhythm) and "backup" pacing if bradycardia (slow heart rhythm) occurs. They also offer a host of other sophisticated functions such as storage of detected arrhythmic events and the ability to perform electrophysiologic testing. Stored information can help your doctor optimize the ICD for your needs.

What should I ask my doctor or nurse about living with an ICD?

You most likely can resume a near normal lifestyle. But, it is best to ask your doctor what types of machines or equipment you should avoid. Also ask what you can and cannot do when you have an ICD. Read about living with an ICD. Download ICD Questions to Ask Your Doctor for suggested questions for your healthcare providers, such as:

• When can I resume normal activities?
• Can I swim?
• Can I run?
• Can I have sex?
• Can I play video games and use wireless devices?
• What will the ICD feel like day to day?
• When can I expect a shock?
• Does the shock hurt?