In implantable cardioverter-defibrillator therapy, which statement best describes the difference between primary and secondary prevention?

• A. Primary: therapeutic after a cardiac event; Secondary: prophylactic
• B. Primary: prophylactic; Secondary: positive event (SCD) or EP study
• C. Primary: prophylactic; Secondary: routine testing only
• D. Primary: palliative; Secondary: curative

Answer: (B)

The key idea is distinguishing risk-based prevention from event-based prevention in ICD therapy. Primary prevention means we implant the device to prevent the first Sudden Cardiac Death in patients who are at high risk but have not yet had a life-threatening arrhythmia. This is a prophylactic use aimed at stopping a potential future event. Secondary prevention, on the other hand, is for patients who have already experienced a life-threatening arrhythmia, such as a survived SCD or sustained VT, and the ICD is implanted to prevent recurrence. An electrophysiology study that shows inducible VT/VF also supports secondary prevention because it demonstrates susceptibility to dangerous arrhythmias, indicating the need to prevent another event. So, describing primary as prophylactic and secondary as based on a prior event (SCD) or an inducible arrhythmia on EP study captures the fundamental distinction.