An Implantable Cardioverter-Defibrillator (ICD) is a surgically implanted device used to monitor heart rhythms and deliver electrical shocks to treat life-threatening, rapid arrhythmias like ventricular tachycardia or fibrillation. It acts as a 24/7 safety net to prevent sudden cardiac death in high-risk patients.

Treating Dangerous Arrhythmias:

The main function is to detect and stop rapid, abnormal heart rhythms (ventricular tachycardia or fibrillation) that can lead to sudden cardiac arrest.

Delivering Therapy:

If a dangerous arrhythmia is detected, the ICD delivers a high-energy shock (defibrillation) to reset the heart's rhythm, or, it can use "overdrive pacing" (a rapid series of, often imperceptible, pulses) to stop less severe fast rhythms.

Preventing Sudden Cardiac Death (SCD):

It is used for primary prevention in patients at high risk for fatal arrhythmias, and secondary prevention for those who have already survived a cardiac arrest or similar event.