A 52-year-old man with known heart failure has an ECG showing sinus rhythm with QRS duration 155 ms, left bundle branch block morphology, and LVEF 30%. Despite 3 months of optimized GDMT, he remains in NYHA class III. What is the next evidence-based intervention?

• A Add hydralazine-isosorbide dinitrate combination
• B Add ivabradine to reduce heart rate further
• C Refer for implantable cardioverter-defibrillator (ICD) for primary prevention
• D Upgrade to cardiac resynchronization therapy (CRT) ✓

Explanation

CRT is indicated in patients with LVEF ≤35%, sinus rhythm, LBBB morphology, and QRS duration ≥150 ms who remain NYHA class II-IV despite optimized medical therapy (MADIT-CRT and RAFT trials). The QRS threshold of 150 ms with LBBB morphology gives the strongest benefit. ICD alone does not improve symptoms or reduce heart failure hospitalizations; CRT does. Ivabradine requires resting HR ≥70 bpm on maximized beta-blocker but does not address mechanical dyssynchrony.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.