Which scenario represents a secondary prevention indication for defibrillator therapy?

• A. Recurrent syncope due to vasovagal
• B. Atrial fibrillation with rapid ventricular response
• C. Stable angina
• D. Prior VF or unstable VT without reversible cause

Answer: (D)

Secondary prevention ICD therapy is indicated in patients who have already survived a life-threatening ventricular arrhythmia or cardiac arrest due to ventricular fibrillation or sustained ventricular tachycardia, with no reversible cause identified. This scenario matches that criterion because it describes prior ventricular fibrillation or unstable VT without a reversible cause, which is precisely when an ICD is used to prevent recurrence. The other options involve non-life-threatening or non-ventricular tachyarrhythmias (vasovagal syncope, atrial fibrillation with rapid conduction) or stable angina, none of which reflect a prior malignant ventricular arrhythmia. Thus, prior VF or unstable VT without reversible cause is the secondary prevention indication.