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What is an implantable cardioverter-defibrillator (ICD)?

Posted By Anthony Komaroff, M.D. On April 26, 2012 @ In Heart Health | Comments Disabled


I have a heart arrhythmia. My doctor wants me to get an ICD. What do I need to know before agreeing to get one?


ICD stands for “implantable cardioverter-defibrillator.” It is a small device that is surgically placed in your body. An ICD can save your life — but it can also complicate your life.

Why was the ICD developed? Sometimes the heart develops dangerous irregular rhythms. Two, in particular, are life-threatening. The most dangerous is ventricular fibrillation (VF). When a heart develops VF, it stops pumping. It just quivers; it’s in cardiac arrest. With no blood circulating to your brain, you lose consciousness. If no blood reaches your brain for more than 4 minutes, your brain dies.

Another dangerous rhythm is ventricular tachycardia (VT). Your heart beats rapidly, and your blood still circulates — though less effectively than with a regular rhythm. Unfortunately, if VT is not corrected, it often turns into VF.

About 60 years ago, Harvard doctors invented the defibrillator, a machine that delivers a shock to the heart. They showed that the shock could quickly return a dangerous heart rhythm to normal. The shock was delivered by two paddles placed on a patient’s chest. Obviously, the defibrillator could help you only if your dangerous heart rhythm was diagnosed and treated within minutes of its starting. You had to be in a medical setting, or emergency medical technicians had to get to you very quickly.

In recent years, machines to deliver these shocks are also located at airports, on airplanes and in other public places. Still, most people who develop VT or VF are nowhere near a defibrillator.

Enter the ICD, which has two basic functions. First, it reads your heart rhythm and spots a potentially dangerous one. Second, it sends a jolt of electricity to your heart muscle to end the dangerous rhythm and restore a normal rhythm. The only people for whom an ICD is recommended are people who have had VT or VF, or who have a heart condition that greatly increases their risk of developing these dangerous rhythms.

An ICD is about the size of a deck of cards. The main part, called the pulse generator, is implanted underneath the skin just below the collarbone. Special wires called leads (pronounced “leeds”) connect the pulse generator to the heart. The leads constantly sense the heart’s rhythm and can deliver a large jolt of electricity to halt an abnormal heart rhythm and restore a healthy one.


When you have an ICD placed in your body, it’s as if the doctor with the paddles is always with you. It can be life-saving. However, some people become anxious or depressed by the possibility of having a shock at any time — even though they need it, and even though it may save their life.

ICDs don’t last forever. The pulse generator needs replacement every three to seven years, but it’s a pretty simple procedure. Occasionally, the wires to the heart need to be replaced. This is a bigger procedure, requiring anesthesia. Some states have driving restrictions for people with ICDs.

Finally, ICD recipients have for years been told to avoid magnetic resonance imaging (MRI), because it could damage the ICD. A recent study found that certain adjustments of the ICD before the MRI can often solve that dilemma.

In many cases, the benefits of an ICD outweigh the drawbacks. But before you give your OK, talk to your doctor about an ICD’s potential to save your life — and also alter the quality of it.

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