Which statement best describes the primary prevention indication for ICD?

• A. Heart failure with preserved EF
• B. MI with EF >50%
• C. NYHA I with normal EF
• D. MI with EF <30% or EF <35% with NYHA II-III

Answer: (D)

The main concept here is identifying who benefits from an ICD for primary prevention after a myocardial infarction. An ICD lowers mortality by preventing sudden cardiac death due to ventricular tachyarrhythmias in patients with substantial left ventricular dysfunction, typically after MI, when the risk is highest.

The best statement captures the established thresholds: after MI, an ICD is indicated if the left ventricular ejection fraction is very low (generally <30%), or if it is 35% or higher but the patient has moderate symptoms (NYHA class II–III). In these patients, despite optimal medical therapy, the risk of dangerous arrhythmias remains high enough that an ICD provides a mortality benefit.

It helps to remember that this protection is focused on primary prevention—patients who have not yet had a life-threatening arrhythmic event but are at elevated risk due to poor systolic function. Other scenarios listed—heart failure with preserved EF, MI with a preserved EF, or mild/no symptoms with relatively normal EF—do not meet the criteria for primary prevention ICDs.

So the statement that aligns with guideline-based primary prevention criteria is: after MI with an EF less than 30%, or EF less than 35% with NYHA II–III symptoms.