What is the difference between a pacemaker and an ICD?

• A. A pacemaker is implanted in the liver; an ICD is in the heart.
• B. A pacemaker stimulates the heart to beat normally; an ICD shocks the heart during dangerous rhythms.
• C. A pacemaker cures heart failure; an ICD cures arrhythmias.
• D. A pacemaker measures blood flow; an ICD monitors.

Answer: (B)

The main concept is how these devices manage heart rhythm in different ways: a pacemaker provides pacing to prevent the heart from beating too slowly, while an ICD is designed to detect and terminate dangerous fast rhythms.

A pacemaker sends small electrical impulses to stimulate the heart to beat at a normal rate when the intrinsic rate is too slow or when conduction is impaired. It helps prevent symptoms from bradycardia, such as dizziness or fainting, by ensuring a steady heart rate.

An ICD continuously monitors the heart and, if it detects a life-threatening fast rhythm like ventricular tachycardia or ventricular fibrillation, delivers therapy to restore normal rhythm. This therapy is typically a shock, and it may also include anti-tachycardia pacing. Some devices can also provide pacing if needed after a shock.

In practice, a pacemaker shields against slow heart rates, while an ICD guards against sudden, dangerous fast rhythms. Some advanced devices combine both functions, but the core distinction remains: pacing for bradycardia versus defibrillation/anti-tachycardia therapy for tachyarrhythmias.