Which condition is an indication for primary prevention implantable cardioverter-defibrillator placement?

• A. MI with EF <50%
• B. NYHA I with EF 60%
• C. MI with EF <30% or EF <35% with NYHA II-III
• D. Hypertension with normal EF

Answer: (C)

Primary prevention ICDs are placed in patients with significant risk of sudden death due to reduced left ventricular function, even before a life-threatening arrhythmia occurs. The strongest indications come from having an ejection fraction that is severely depressed, because that level of dysfunction correlates with a high risk of malignant ventricular rhythms.

If someone has had a myocardial infarction and their LV ejection fraction is 30% or less, that alone is a strong cue for ICD implantation for primary prevention. If the EF is in the 30–35% range but the patient has ongoing heart failure symptoms (NYHA class II–III), that combination also supports ICD placement. These thresholds reflect the balance between risk reduction with the device and the patient’s overall functional status.

In contrast, other scenarios don’t meet the criteria: an EF of 60% with no significant symptoms doesn’t carry enough risk to justify an ICD, and hypertension with a normal EF doesn’t indicate a high risk of sudden death requiring device therapy. It’s also important to be post–MI for a period and on optimal medical therapy before considering implantation.