Implantable Cardioverter Defibrillator (ICD)

The primary function of an ICD is to recognize and treat dangerous fast heart rhythms from the lower chambers of the heart (ventricles) such as ventricular tachycardia and ventricular fibrillation.

First introduced in the early 1990s, these devices have undergone a tremendous evolution, with an ever-decreasing size yet with increasing power and complexity. Similar to a pacemaker (indeed each ICD also incorporates a fully functional pacemaker), these devices consists of a generator (a battery and electronic circuits) and one or more electrode leads, threaded through a vein under the collarbone to the inside of the heart chambers.

Several important differences need to be mentioned: compared to a pacemaker generator, the ICD generator is significantly larger (about the size of a small pager) and unlike a pacemaker, the ICD can recognize and effectively treat fast heart rhythm problems.

The ICD is very effective in terminating fast abnormal heart rhythms, either by shock (defibrillation/cardioversion) or by means of overdrive pacing.

Several large clinical studies have recently shown that, when added to optimal medical therapy, the ICD can reduce the death rate in patients with severe heart disease by 30–45%. Individuals with an ICD should receive regular follow up to assure proper function of the device and assess the battery status.