implantable cardioverter-defibrillator

Imagine a built-in lifeguard and a defibrillator combined into one small device that lives inside the body, always watching. An implantable cardioverter-defibrillator (ICD) continuously monitors the heart’s rhythm and, if it detects a life-threatening fast rhythm from the lower chambers, delivers an internal electrical shock to reset the heart back to normal.

Like a pacemaker, an ICD has a generator placed under the skin and leads running into the heart, and it can pace a slow heart too. Its defining job, though, is recognizing dangerous ventricular arrhythmias — ventricular tachycardia and ventricular fibrillation — that would otherwise cause sudden cardiac death. It may first try painless rapid pacing to break the rhythm, and if that fails, fire a shock within seconds.

ICDs are used to prevent sudden death in people at high risk — for example after a large heart attack with a weakened pump, in certain cardiomyopathies, or after surviving a cardiac arrest. They protect against fatal rhythms but do not prevent the rhythm from starting or fix the underlying heart disease, so medications and treatment of the root cause continue alongside the device.