Implantable Cardioverter-Defibrillator (ICD)

Search Knowledgebase

Topic Contents

Implantable Cardioverter-Defibrillator (ICD)

Topic Overview

An implantable cardioverter-defibrillator (ICD), also known as an automatic implantable cardioverter-defibrillator (AICD), is a small device that doctors use to watch for and fix life-threatening abnormal heart rhythms. The doctor surgically implants the defibrillator under the skin, usually below the left collarbone. A wire threaded through a large vein connects the device to the heart.

If you have had a serious episode of an abnormally fast heart rhythm or are at high risk for having one, you may need an ICD. If you have coronary artery disease, heart failure, or a problem with the structure or electrical system of the heart, you may be at risk for an abnormal heart rhythm.

How does an ICD work?

An ICD continuously monitors your heart. If it detects a life-threatening rapid heart rhythm, it sends an electric shock to your heart to restore a normal rhythm. The device then goes back to its monitoring mode.

After the shock, your heart may beat very slowly for several minutes. So ICDs also act as pacemakers, sending weaker shocks that pace the heart if the rate falls below a certain preset level.

Your doctor sets both the rate at which a shock will occur and the level of shock needed to convert to a normal rate and rhythm. If the first shock does not reset your heart rhythm, the device will send progressively stronger shocks until the heart converts to a normal rate.

Although an ICD effectively treats life-threatening episodes of abnormal heart rhythms, it does not prevent them. You will also need to take a medicine to prevent or at least decrease how often you have abnormal heart rhythms so that you are not getting too many shocks.

An example of a life-threatening heart rhythm is ventricular tachycardia.

Living with an ICD

You may feel worried by the possibility of being shocked. The shock itself can be uncomfortable—it may feel as if you are being kicked in the chest. You may pass out before the device fires, and you likely won't remember the shock. Be reassured, though, that the shock is life-saving.

Know what to do after a shock

Be sure you have a plan for what to do if you get a shock from your ICD. Talk to your doctor if you need to make a plan. In general, your plan depends on how you feel after you get a shock and how many times you get a shock.

Know what to stay away from

Strong electric or magnetic fields can interfere with the ICD. Most electrical equipment and household appliances create very weak magnetic fields and do not interfere with ICDs. So you can safely use most household and office equipment. And you can usually avoid electrical interference from magnetic or electrical sources by keeping certain things a few inches away from your pacemaker or ICD. You should completely avoid things like heavy electrical or industrial equipment.

The table below lists electrical and magnetic sources that are safe and sources that you should avoid. This table does not list all magnetic or electrical sources that you might use. Ask your doctor about the safety of sources not listed here.

Safety guidelines for ICDs

Stay away from:

  • CB or ham radios.
  • High-voltage power lines. Stay at least 7.5 m (25 ft) away.
  • Large magnets.
  • MRI machines. An MRI uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body.

Use with caution:

  • Cell phones:
    • Do not carry a cell phone in a pocket directly over the pacemaker or ICD.
    • Hold the phone to the ear on the side away from your device.
    • Keep a phone at least 15 cm (6 in.) away from the pacemaker or ICD.
  • Keep the following devices at least 30 cm (12 in.) away from the pacemaker or ICD:
    • Arc welders
    • Battery-powered cordless power tools
    • Industrial power generators
    • Magnets
    • Magnetic wands used at airports
    • Stereo speakers
    • Radio transmitters (including those used in toys)

Safe to use:

  • Kitchen and bathroom equipment:
    • Bathroom appliances (electric razors, curling irons, and hair dryers)
    • Kitchen appliances (such as toasters, blenders, electric can openers, and refrigerators)
    • Microwave, gas, and electric ovens
  • Other household items:
    • Electric tools (such as drills and table saws)
    • Lawn and garden equipment (such as mowers and leaf blowers)
    • Heating pads and electric blankets
    • Washing machines and dryers
    • Phones (landline phones including cordless models)
    • Remote controls
    • TVs, VCRs, CD players, DVD players
  • Office equipment:
    • Computers
    • Copy machines
    • Fax machines
    • Printers

Know when you can drive again

Driving is something else you need to think about if you have an ICD. Talk to your doctor about whether you should restrict your driving. Your doctor will check your medical history and review your risk of having another arrhythmia that could make driving unsafe. To help doctors with this decision, the American Heart Association and Heart Rhythm Society recommend the following driving restrictions:1, 2

  • If you get an ICD because you are at risk for a life-threatening arrhythmia (but have never had one), you should not drive for at least 1 week afterward to allow time to heal. After you heal, you can drive again as long as your ICD has never given you a shock and you have no symptoms of an arrhythmia. But keep in mind that an arrhythmia could cause you to pass out (lose consciousness).
  • If you get an ICD because you have already had a life-threatening arrhythmia, you should wait at least 6 months before you drive again.
  • If you have an ICD that has given you a shock for an arrhythmia, you should wait at least 6 months before you drive again.

Know how to be safe when exercising

Ask your doctor what sort of activity and intensity is safe for you. Talk with your doctor about what you need to know before exercising with an ICD. Follow exercise safety tips, such as one that says to stop exercising if you feel dizzy or light-headed.

Follow-up care

It is important to keep your regular follow-up appointments with your doctor. He or she will check the device to see whether it has delivered any shocks since your last visit. This will help your doctor know if your medicines need to be adjusted. During your follow-up visits, your doctor will also check the battery and replace it at regular intervals.

Your doctor and/or the device maker will contact you about what to do if your device has been recalled.

When to call a doctor

Call your doctor right away if you have symptoms that could mean your device is not working properly, such as:

  • Your heartbeat is very fast or slow, skipping, or fluttering.
  • You feel dizzy, light-headed, or faint.
  • You have shortness of breath that is new or getting worse.

After an ICD shock

Be sure you have a plan for what to do if you get a shock. Talk to your doctor if you are not sure. In general, your plan depends on how you feel after you get a shock and how many times you get a shock.

After one shock:

  • Call 911 or other emergency services immediately if you feel bad or have symptoms like chest pain.
  • Call your doctor soon if you feel fine right way. Your doctor may want to talk about the shock and schedule a follow-up visit.

After a second shock within 24 hours:

  • Call your doctor immediately, even if you feel fine right away.

Infection near the ICD

Call your doctor right away if you think you have an infection near your ICD. Signs of an infection include:

  • Changes in the skin around your ICD, such as:
    • Swelling.
    • Warmth.
    • Redness.
    • Pain.
  • Unexplained fever.

Other Places To Get Help


Canadian Cardiovascular Society
222 Queen Street
Suite 1403
Ottawa, ON  K1P 5V9
Phone: 1-877-569-3407 toll-free
(613) 569-3407
Fax: (613) 569-6574
Web Address:

The Canadian Cardiovascular Society works to advance the cardiovascular health and care of Canadians through leadership, research, and advocacy.

Heart and Stroke Foundation of Canada
222 Queen Street
Suite 1402
Ottawa, ON  K1P 5V9
Phone: (613) 569-4361
Fax: (613) 569-3278
Web Address:

The Heart and Stroke Foundation of Canada works to improve the health of Canadians by preventing and reducing disability and death from heart disease and stroke through research, health promotion, and advocacy.

Heart Rhythm Society
1400 K Street NW
Suite 500
Washington, DC  20005
Phone: (202) 464-3400
Fax: (202) 464-3401
Web Address:

The Heart Rhythm Society provides information for patients and the public about heart rhythm problems. The Web site includes a section that focuses on patient information. This information includes causes, prevention, tests, treatment, and patient stories about heart rhythm problems. You can use the Find a Specialist section of the Web site to search for a heart rhythm specialist practicing in your area.

U.S. National Heart, Lung, and Blood Institute (NHLBI)
P.O. Box 30105
Bethesda, MD  20824-0105
Phone: (301) 592-8573
Fax: (240) 629-3246
TDD: (240) 629-3255
Web Address:

The U.S. National Heart, Lung, and Blood Institute (NHLBI) information center offers information and publications about preventing and treating:

  • Diseases affecting the heart and circulation, such as heart attacks, high cholesterol, high blood pressure, peripheral artery disease, and heart problems present at birth (congenital heart diseases).
  • Diseases that affect the lungs, such as asthma, chronic obstructive pulmonary disease (COPD), emphysema, sleep apnea, and pneumonia.
  • Diseases that affect the blood, such as anemia, hemochromatosis, hemophilia, thalassemia, and von Willebrand disease.



  1. Epstein AE, et al. (1996). Personal and public safety issues related to arrhythmias that may affect consciousness: Implications for regulation and physician recommendations. A medical/scientific statement from the American Heart Association and the North American Society of Pacing and Electrophysiology. Circulation, 94(5): 1147–1166.
  2. Epstein AE, et al. (2007). Addendum to Personal and public safety issues related to arrhythmias that may affect consciousness: Implications for regulation and physician recommendations: A medical/scientific statement from the American Heart Association and the North American Society of Pacing and Electrophysiology. Public safety issues in patients with implantable defibrillators. A scientific statement from the American Heart Association and the Heart Rhythm Society. Circulation, 115(9): 1170–1176.

Other Works Consulted

  • Baddour LM, et al. (2010). Update on cardiovascular implantable electronic device infections and their management. A scientific statement from the American Heart Association. Circulation, 121(3): 458–477.
  • Lampert R, et al. (2010). HRS Expert consensus statement on the management of cardiovascular implantable electronic devices (CIEDs) in patients nearing end of life or requesting withdrawal of therapy. Heart Rhythm, 7(7): 1088–1026. Available online:
  • Sears SF, et al. (2005). How to respond to an implantable cardioverter-defibrillator shock. Circulation, 111(23): e380–e382.


By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Primary Medical Reviewer Brian D. O'Brien, MD - Internal Medicine
Specialist Medical Reviewer Robert A. Kloner, MD, PhD - Cardiology
Last Revised October 14, 2010

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information.