Which ECG pattern best indicates right ventricular involvement in an inferior MI?

• A. ST elevation in II > III
• B. ST elevation in aVL
• C. ST elevation in V5
• D. ST elevation in III > II

Answer: (D)

The main idea here is recognizing right-ventricular involvement in an inferior myocardial infarction on the surface ECG. When the RCA causes an inferior MI and the right ventricle is involved, the injury current shifts so that the ST segment is more elevated in lead III than in lead II. This relative prominence of ST elevation in III reflects the direction of the infarct vector toward the right ventricle.

Why this is the best clue: in inferior MI the typical changes appear in leads II, III, and aVF, but involvement of the right ventricle specifically alters the vector so that III shows greater ST elevation than II. Other patterns—like ST elevation in aVL (a lateral lead) or in V5 (a lateral/precordial lead)—point to lateral wall involvement rather than the right ventricle. Right-sided RV involvement is best confirmed by looking at right-sided leads (such as V4R), but among the given options, a greater ST elevation in III than II is the classic indicator of RV involvement with an inferior MI.

In practice, if the clinical picture supports RV involvement (often with hypotension and clear lungs), expect III to be higher than II on the standard limb leads, and consider checking right-sided leads for confirmation.