On an ECG, a patient with acute inferior STEMI (ST elevation II, III, aVF) also shows ST elevation in V4R. This finding indicates involvement of which vessel?

• A Left anterior descending artery (proximal)
• B Left circumflex artery
• C Right coronary artery (proximal, before RV branches) ✓
• D Posterior descending artery only

Explanation

ST elevation in right-sided lead V4R indicates right ventricular MI, which complicates proximal right coronary artery occlusion (before the RV marginal branches). Right ventricular infarction is critical to identify because these patients are preload-dependent and nitrates should be avoided (risk of severe hypotension). Management requires volume loading. LCx occlusion causes posterior/inferior MI but rarely RV involvement.

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

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Written and medically reviewed by the StethoPrep medical team.