An implantable cardioverter defibrillator (ICD) is a device that is implanted in a patient’s chest and can be programmed to monitor for and, if necessary, correct an abnormal heart rhythm (arrhythmia). If the heartbeat gets too fast (ventricular tachycardia) the ICD will stimulate the heart to restore a normal rhythm (anti-tachycardia pacing). In potentially fatal cases where the heart no longer beats but merely “quivers” or fibrillates (ventricular fibrillation) the ICD can deliver an electric shock (defibrillation) to “reset” the heartbeat.

The ICD has an electronic memory that a physician can retrieve during follow up visits or even by telephone (transtelephonic monitoring). The memory stores information such as:

An ICD is similar in many respects to a pacemaker, which is another type of device that corrects an abnormal heart rhythm. However, pacemakers are usually chosen to correct a heart rhythm that is too slow (bradycardia), whereas ICDs are commonly used to detect and correct a heart rhythm that is too fast (ventricular tachycardia). Pacemakers cannot deliver the high energy electrical shock required for defibrillation. However, ICDs can be programmed to function as a pacemaker, and combination devices are available to detect and treat multiple heart rhythm problems in the same patient.