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Am Fam Physician. 1998;57(2):310-312

See related article on cardioverter-defibrillators.

What is an implantable cardioverter-defibrillator?

An implantable cardioverter-defibrillator system (often called an ICD) includes a pulse generator and one or more leads that are put into (surgically implanted in) your body. The pulse generator, which constantly watches your heart beat, is like a small computer. It runs on a battery. The lead (say: leed) is a wire from the pulse generator that connects to the inside of your heart. The ICD may have one or more leads. The lead takes signals from your heart to the ICD and then takes energy from the pulse generator to your heart.

Your doctor (or a special doctor called an electrophysiologist) will use a programmer to communicate (“talk”) with the defibrillator. The programmer has a wand that is held on top of the ICD (over your skin). It can send signals to the ICD and receive signals from the ICD. Your doctor can use the programmer to change the setting on the ICD. The defibrillator also stores information when you have a fast heart rhythm. Your doctor can use the wand to get a picture of the fast heart rhythm. This picture (called a tracing) can help your doctor decide the best treatment for you.

Why might I need an ICD?

Normally, your heart has a natural pacemaker that helps your heart beat steadily. An electrical impulse starts in one of the upper chambers (called the atria) of the heart and goes through the heart to the bottom chambers (called the ventricles). You may need an ICD if you have had, or are at high risk of having, ventricular tachycardia or ventricular fibrillation (these are names of different heart rhythm problems).

Your heart's electrical system may develop a problem that makes your heart beat too fast. When the electrical problem comes from the bottom chambers of the heart, the rhythm disturbance is called ventricular tachycardia. When your heart goes into ventricular tachycardia, it doesn't pump blood as well. As a result, less blood is pumped to your body and your brain. You may feel your heart pounding, or you may feel dizzy or faint. If ventricular tachycardia isn't treated properly, it can be life-threatening.

When a ventricular arrhythmia becomes very fast and irregular, it's called ventricular fibrillation. The heart just quivers, and no blood is pumped to the body or the brain. A person with ventricular fibrillation usually passes out very quickly. Unless treatment is given in five to 10 minutes, ventricular fibrillation causes death.

In people who don't have an ICD, ventricular fibrillation is treated with an external defibrillator. Paddles are put on the outside of the chest, and an electrical shock is given through the paddles. This shock goes through the heart and stops the irregular beat. The heart then goes back to a more regular rhythm.

Unfortunately, ventricular fibrillation can occur without warning—often, treatment can't be given in time. An ICD may be recommended for you because your doctor thinks you're at high risk for having ventricular fibrillation. The ICD can quickly recognize and stop ventricular fibrillation.

How does the ICD work?

The ICD constantly “watches” your heart rhythm. If it “sees” that your heart is beating fast, it delivers the treatment programmed by your doctor. The types of treatment it can deliver are pacing, cardioversion and defibrillation.

  • Pacing. If you have ventricular tachycardia that isn't too fast, the ICD can deliver several pacing signals in a row. When those signals stop, the heart may go back to a normal rhythm. No other treatment is needed.

  • Cardioversion. If the pacing doesn't work, cardioversion can be used. In cardioversion, a mild shock is sent to the heart to stop the fast heartbeat.

  • Defibrillation. If ventricular fibrillation is detected, a defibrillation shock is sent. This stronger shock can stop the fast rhythm and help the heartbeat go back to normal. The ICD can also “see” when your heart beats too slowly. It can act like a pacemaker and bring your heart rate up to normal.

What does treatment with an ICD feel like?

Some people may not feel anything when the ICD delivers pacing therapy for ventricular tachycardia. Other people feel a fluttering in their chest. They usually say that it doesn't feel uncomfortable or painful.

Cardioversion is stronger than a pacing pulse. It feels like being thumped in the chest.

The defibrillator shock is the strongest treatment. Many people say it feels like being kicked in the chest. It usually comes suddenly and lasts only a second. Some people are upset for a short time after a defibrillator shock, but other people feel reassured that the ICD is treating their heart rhythm problem.

Pacing a slow heart rate uses very little energy. You may not feel this treatment at all.

How is a cardioverter-defibrillator implanted?

Before the ICD is implanted, your doctor will look at your size and shape, note any previous chest surgeries you may have had and the activities that you like to do. The pulse generator may be implanted either under your collarbone on the left or right side of your chest, or in your abdomen (tummy area). In either place, the generator can be put in a “pocket” the doctor makes under your skin or, sometimes, in your muscles. One end of the lead wire is put into a vein that goes to your heart. The wire is moved through the vein until it reaches the heart. The other end of the wire is attached to the pulse generator. When the system is in place, your doctor will make your heart go into a fast rhythm to test the ICD. At this time, the doctor will program the ICD to treat your specific heart rhythm problem.

How will an ICD affect my lifestyle?

So that you can heal well, your doctor will want you to limit your activities for the first few weeks after you get the ICD. Then you can slowly go back to your normal lifestyle. Depending on your condition and your local laws, your doctor will tell you when it's safe for you to drive a car. In general, you can expect to be back to normal after a month.

You'll need to stay away from machinery that could interfere with your ICD. You shouldn't work near strong magnetic fields or strong electrical fields. The ICD is built to be protected from most home shop tools and electrical appliances, including microwave ovens. However, you need to be certain that all electrical items are properly grounded and in good repair. Your doctor will help you understand what to avoid when you have an ICD.

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