Implantable Cardioverter-Defibrillators (ICDs)

What is an implantable cardioverter-defibrillator (ICD)?

The implantable cardioverter-defibrillator (ICD) is a device designed to shock the heart back into a normal rhythm to prevent sudden death. It is a complex collection of electronic circuits, batteries, and electrodes small enough to be put under the skin. The ICD system consists of:

• a pulse generator that can send a powerful shock to the heart
• electrodes to sense the rhythm of the heart and to deliver the shock to the heart muscle
• batteries designed to last 4 to 5 years and deliver about 100 shocks
• an electronic logic circuit to tell the ICD when to discharge.

If the heart is beating normally, the ICD is inactive. When an abnormal, fast heart rate, known as ventricular tachycardia, is detected, the ICD will first try to pace the heart faster than the tachycardia to stop the abnormal rhythm. If this doesn’t work, or the rhythm changes to ventricular fibrillation (fluttering heartbeat), the ICD sends electric shock signals to the heart. The electric shock converts the abnormal rhythm to a normal rhythm. The device is inserted under the skin in the chest. The procedure is similar to that of a pacemaker implantation. The ICD also has the ability to function as a pacemaker.

Why are ICDs needed?

Some people are at very high risk for sudden death. This group includes those whose heart suddenly stops pumping blood due to a loss of an organized heartbeat (ventricular fibrillation or VF). ICDs are also used in people with a type of very rapid heartbeat (ventricular tachycardia or VT) can result in loss of consciousness or death.

Coronary care units in hospitals are prepared to treat problems like VT and VF. An electric shock across the chest (defibrillation) is given to convert an abnormal rhythm and rate to normal. Many episodes, however, occur outside hospitals. People die because electric shock treatment is not available. It is now possible to identify those at high risk of sudden death. The ICD is designed for those people.

Who is a candidate for an ICD?

Candidates for an ICD fall into three categories:

• those with long episodes of VT
• those who have survived VF
• those whose heart problems put them at high risk for VT or VF.

Many of these people will require a special test called an electrophysiological study (EPS) before receiving an ICD. This test measures how much the heart is at risk for an event that could prove fatal. It is used to help decide whether to use an ICD or whether to use drugs for treatment.

What are the benefits?

For people who are candidates for ICDs, the devices prolong life. For many people, the device provides peace of mind, relieving any concern about dying without warning. Some can resume driving without worry. The ICD does not fix existing heart problems, but reduces the risk of dying from an abnormal heart rhythm.

What are the risks?

There is risk with every treatment or procedure. Talk to your provider for complete information about how the risks apply to you. Once the ICD is implanted, you will need to make regular visits to the doctor so the device can be monitored. Monitoring shows whether the device is sensing the heartbeat properly, how many shocks have been delivered, and how much power is left in the batteries.

The most common problem with the device is that it sometimes delivers shocks when you do not need them. You are usually quite aware of each shock, even though it lasts only a very short time. Your doctor should be notified of every shock you feel. When the batteries have run down, the pulse generator must be replaced. Replacement of the pulse generator requires only minor surgery.

Some electrical equipment can interfere with the ICD. This equipment includes MRI scans, digital cellular phones, metal detectors at airport security gates, heavy-duty electrical power equipment, arc welders, a running car engine (do not lean over the engine), and certain electrical power surgical tools. It is safe for people with ICDs to be around most household electrical appliances.

What happens after ICD implantation?

Recovery time after surgery to implant one of the newer ICD units is quite short. Hospital stays are usually no more than overnight, and there is quick return to prior activity levels.

People with ICDs still need to follow their cardiologist advice about medication, diet, and exercise.