An implantable cardioverter defibrillator (ICD) is a potentially lifesaving medical device that is placed inside the body. An ICD treats life-threatening abnormal heart rhythms (called arrhythmias), including ventricular fibrillation, which makes the heart's large muscular chambers (the ventricles) quiver without actually squeezing and pumping. When this happens, there is no real heartbeat and not enough blood flows to the brain or other organs, including the heart. As a result, a person with ventricular fibrillation passes out and can die within minutes.
An ICD is made of two parts. The pulse generator looks like a small box. It is implanted under the skin below the collarbone. The box contains a lithium oxide battery (which lasts about five to nine years) and electrical components that analyze the heart's electrical activity. Connected to the pulse generator are one or more electrodes, which travel to the heart. When the ICD senses an abnormal heart rhythm, it administers a brief, intense electrical shock to the heart, correcting the abnormal rhythm. Many people say that the shock feels like being punched in the chest, although the amount of discomfort varies.
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