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 treat 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 the following therapies:

  • Low-energy pacing therapy. You may feel nothing or a painless fluttering in your chest when your ICD responds to mild disruptions in your heartbeat.
  • Cardioversion therapy. A higher energy shock is delivered for a more serious heart rhythm problem. It may feel as if you're being thumped in the chest.
  • Defibrillation therapy. This is the strongest form of electrical therapy used to restore a normal heartbeat. During this therapy, it may feel as if you're being kicked in the chest, and it might knock you off your feet.

    The pain from this therapy usually lasts only a second. There should be no 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. Frequent shocks in a short time period are known as ICD storms. If you have ICD storms, 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 be programmed to perform other functions, which include:

  • Antitachycardia (tak-ih-KAHR-dee-uh). If you have an unusually fast heart rate, the ICD delivers painless, low-energy impulses that pace or stimulate the heart to beat normally. This can prevent the need for cardioversion or defibrillation.
  • Pacemaker. Most modern ICDs can also function as a pacemaker, delivering low-energy impulses that stimulate the heart to beat normally.
  • Recording heart activity. The ICD records information about variations in your heart's electrical activity and rhythm. This information helps your doctor evaluate your heart rhythm problem and, if necessary, reprogram your ICD.

Subcutaneous ICD

This newer type of ICD, available at some surgical centers, is implanted under the skin without the wires that attach to the heart. You may be a candidate for this device if you have structural defects in your heart that prevent attaching wires to it.

Implanting a subcutaneous ICD is less invasive than an ICD that attaches to the heart, but the device is larger and doesn't perform as many functions as 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 (dilated cardiomyopathy) or thickened (hypertrophic cardiomyopathy) 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.
  • Having other rare conditions such as Brugada syndrome and arrhythmogenic right ventricular dysplasia also may mean you need an ICD.
June 14, 2016
References
  1. Implantable cardioverter defibrillator. National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/icd/icd_all.html. Accessed April 4, 2016.
  2. Ganz LI. General principles of the implantable cardioverter-defibrillator. http://www.uptodate.com/home. Accessed April 4, 2016.
  3. Epstein AE, et al. 2012 ACC/AHA/HRS focused update incorporated into the ACC/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities. Circulation. 2013;127:e283.
  4. Devices that may interfere with implantable cardioverter defibrillators (ICDs). American Heart Association. http://www.heart.org/HEARTORG/Conditions/Arrhythmia/PreventionTreatmentofArrhythmia/Devices-that-may-Interfere-with-Implantable-Cardioverter-Defibrillators-ICDs_UCM_448464_Article.jsp. Accessed April 4, 2016.
  5. Living with your implantable cardioverter defibrillator (ICD). http://www.heart.org/HEARTORG/Conditions/Arrhythmia/PreventionTreatmentofArrhythmia/Living-With-Your-Implantable-Cardioverter-Defibrillator-ICD_UCM_448462_Article.jsp. American Heart Association. Accessed April 4, 2016.
  6. AskMayoExpert. Implanted cardiac devices. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2015.
  7. Ganz LI. Implantable cardioverter-defibrillators: Complications. http://www.uptodate.com/home. Accessed April 4, 2016.
  8. Knight BP. Patient information: Implantable cardioverter-defibrillators (beyond the basics). http://www.uptodate.com/home. Accessed April 4, 2016.