An implantable cardioverter-defibrillator (ICD) is designed to deliver shocks during which abnormal heart rhythm?

• A. Ventricular fibrillation
• B. Bradycardia
• C. Normal sinus rhythm
• D. Atrial flutter

Answer: (A)

An implantable cardioverter-defibrillator is built to recognize dangerous ventricular rhythms and restore a stable heart rhythm with a high-energy shock. In ventricular fibrillation, the ventricles quiver with disorganized electrical activity, producing no effective heartbeat. The ICD delivers a shock to depolarize the heart briefly, interrupt the chaotic activity, and allow the normal conduction system to regain coordinated rhythm. The other rhythms listed don’t indicate this immediate life-threatening ventricular chaos: bradycardia is too slow and often managed with pacing, normal sinus rhythm is already regular, and atrial flutter is an atrial rhythm typically treated with rate control or ablation rather than immediate ventricular defibrillation.