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Who Needs an Implantable Cardioverter Defibrillator?

Implantable cardioverter defibrillators (ICDs) are used in children, teens, and adults. Your doctor may recommend an ICD if you're at risk for certain types of arrhythmia.

ICDs are used to treat life-threatening ventricular arrhythmias, such as those that cause the ventricles to beat too fast or quiver. You may be considered at high risk for a ventricular arrhythmia if you:

  • Have had a ventricular arrhythmia before
  • Have had a heart attack that has damaged your heart's electrical system

Doctors often recommend ICDs for people who have survived sudden cardiac arrest (SCA). They also may recommend them for people who have certain heart conditions that put them at high risk for SCA.

For example, some people who have long QT syndrome, Brugada syndrome, or congenital heart disease may benefit from an ICD, even if they've never had ventricular arrhythmias before.

Some people who have heart failure may need a CRT-D device. This device combines a type of pacemaker called a cardiac resynchronization therapy (CRT) device with a defibrillator. CRT-D devices help both ventricles work together. This allows them to do a better job of pumping blood out of the heart.

Diagnostic Tests

Your doctor may recommend an ICD if he or she sees signs of a ventricular arrhythmia (or heart damage that would make one likely) on the following tests.

EKG (Electrocardiogram)

An EKG is a simple, painless test that detects and records the heart's electrical activity. The test shows how fast the heart is beating and its rhythm (steady or irregular). An EKG also records the strength and timing of electrical signals as they pass through the heart.

A standard EKG only records the heartbeat for a few seconds. It won't detect arrhythmias that don't happen during the test.

To diagnose arrhythmias that come and go, your doctor may have you wear a portable EKG monitor. The two most common types of portable EKGs are Holter and event monitors.

Holter and Event Monitors

A Holter monitor records the heart's electrical activity for a full 24- or 48-hour period. You wear one while you do your normal daily activities. This allows the monitor to record your heart for a longer time than a standard EKG.

An event monitor is similar to a Holter monitor. You wear an event monitor while doing your normal activities. However, an event monitor only records your heart's electrical activity at certain times while you're wearing it.

You may wear an event monitor for 1 to 2 months, or as long as it takes to get a recording of your heart during symptoms.


Echocardiography (echo) uses sound waves to create a moving picture of your heart. The test shows the size and shape of your heart and how well your heart chambers and valves are working.

Echo also can identify areas of poor blood flow to the heart, areas of heart muscle that aren't contracting normally, and injury to the heart muscle caused by poor blood flow.

Electrophysiology Study

For this test, a thin, flexible wire is passed through a vein in your groin (upper thigh) or arm to your heart. The wire records the heart's electrical signals.

Your doctor uses the wire to electrically stimulate your heart. This allows him or her to see how your heart's electrical system responds. The electrical stimulation helps pinpoint where the heart's electrical system is damaged.

Stress Test

Some heart problems are easier to diagnose when your heart is working hard and beating fast. During stress testing, you exercise to make your heart work hard and beat fast while heart tests, such as an EKG or echo, are done. If you can't exercise, you may be given medicine to raise your heart rate.

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Last Updated: November 9, 2011