A patient reports substernal chest pain. Which ECG change should suggest a posterior wall MI?

• A. ST elevation in leads II, III, aVF
• B. ST depression in V1-V3
• C. T wave inversion in lead I
• D. Hyperacute T waves in V4

Answer: (B)

Posterior wall myocardial infarction often goes unrecognized on the standard 12-lead ECG because the injury is on the back of the heart. The electrical disturbance from a posterior infarct creates reciprocal changes that appear on the leads looking at the front of the chest. That means you commonly see ST-segment depression in the anterior chest leads, sometimes with a taller R wave in those same leads as the normal depolarization pattern is altered. In a patient with substernal chest pain, this pattern in the anterior leads is the best clue pointing toward a posterior wall MI.

For comparison, ST elevation in inferior leads points to an inferior wall infarct, T wave inversion in a single lead is nonspecific, and hyperacute T waves in an anterior lead suggest an early anterior infarct rather than posterior.