An implantable cardioverter-defibrillator (ICD) is a small battery-powered device placed in your chest to monitor your heart rhythm and detect irregular heartbeats. An ICD can deliver electric shocks via one or more wires connected to your heart to fix an abnormal heart rhythm.
You might need an ICD if you have a dangerously fast heartbeat (ventricular tachycardia) or a chaotic heartbeat that keeps your heart from supplying enough blood to the rest of your body (ventricular fibrillation). Ventricles are the lower chambers of your heart.
ICDs detect and stop abnormal heartbeats (arrhythmias). The device continuously monitors your heartbeat and delivers electrical pulses to restore a normal heart rhythm when necessary. An ICD differs from a pacemaker — another implantable device used to help control abnormal heart rhythms.
Why it’s done
You’ve likely seen TV shows in which hospital workers “shock” an unconscious person out of cardiac arrest with electrified paddles. An ICD does the same thing only internally and automatically when it detects an abnormal heart rhythm.
An ICD is surgically placed under your skin, usually below your left collarbone. One or more flexible, insulated wires (leads) run from the ICD through your veins to your heart.
Because the ICD constantly monitors for abnormal heart rhythms and instantly tries to correct them, it helps when your heart stops beating (cardiac arrest), even when you are far from the nearest hospital.
How an ICD works
When you have a rapid heartbeat, the wires from your heart to the device transmit signals to the ICD, which sends electrical pulses to regulate your heartbeat. Depending on the problem with your heartbeat, your ICD could be programmed for:
Low-energy pacing. You may feel nothing or a painless fluttering in your chest when your ICD responds to mild disruptions in your heartbeat.
A higher-energy shock. For more-serious heart rhythm problems, the ICD may deliver a higher-energy shock. This shock can be painful, possibly making you feel as if you’ve been kicked in the chest. The pain usually lasts only a second, and there shouldn’t be discomfort after the shock ends.
Usually, only one shock is needed to restore a normal heartbeat. Sometimes, however, you might have two or more shocks during a 24-hour period.
Having three or more shocks in a short time period is known as an electrical or arrhythmia storm. If you have an electrical storm, you should seek emergency care to see if your ICD is working properly or if you have a problem that’s making your heart beat abnormally.
If necessary, the ICD can be adjusted to reduce the number and frequency of shocks. You may need additional medications to make your heart beat regularly and decrease the chance of an ICD storm.
An ICD can also record the heart’s activity and variations in rhythm. This information helps your doctor evaluate your heart rhythm problem and, if necessary, reprogram your ICD.
Other rare conditions that may affect your heart rhythm.Subcutaneous implantable cardioverter-defibrillator (S-ICD)Open pop-up dialog box
A subcutaneous ICD (S-ICD) is a newer type of ICD available at some surgical centers. An S-ICD is implanted under the skin at the side of the chest below the armpit. It’s attached to an electrode that runs along your breastbone.
You may be a candidate for this device if you have structural defects in your heart that prevent inserting wires to the heart through your blood vessels, or if you have other reasons for wanting to avoid traditional ICDs. Implanting a subcutaneous ICD is less invasive than an ICD that attaches to the heart, but the device is larger in size than an ICD.
Who needs an ICD
You’re a candidate for an ICD if you’ve had sustained ventricular tachycardia, survived a cardiac arrest or fainted from a ventricular arrhythmia. You might also benefit from an ICD if you have:
A history of coronary artery disease and heart attack that has weakened your heart.
A heart condition that involves abnormal heart muscle, such as enlarged or thickened heart muscle.
An inherited heart defect that makes your heart beat abnormally. These include long QT syndrome, which can cause ventricular fibrillation and death even in young people with no signs or symptoms of heart problems.