On electrocardiography, which finding defines ST-elevation myocardial infarction?

• A. ST depression
• B. ST elevation in two contiguous leads with reciprocal changes
• C. T wave inversion
• D. Pathologic Q waves

Answer: (B)

ST-elevation myocardial infarction shows acute transmural injury, which on the ECG is demonstrated by ST-segment elevation in two contiguous leads that view the same region of the heart. The elevation reflects a current of injury from sudden coronary occlusion, and you’ll often see reciprocal ST-segment depression in leads opposite the affected wall. This pattern distinguishes STEMI from other ischemic or post-infarction changes.

ST depression alone suggests subendocardial ischemia or NSTEMI rather than a full-thickness, acute infarct. T wave inversion can occur with ischemia or as the infarct evolves, but it does not define an acute STEMI. Pathologic Q waves indicate established, older infarction with scar tissue, not the acute process.