A man, age 65, presents with chest pain and changes on his 12-lead electrocardiogram tracing. Which change suggests an acute myocardial infarction?

• A. ST-segment elevation greater than 1 mm in two or more contiguous leads
• B. ST-segment elevation in aVR
• C. ST-segment depression in II, III, aVF
• D. ST-segment elevation in lead II only

Answer: (D)

ST-segment elevation that signifies a true acute myocardial infarction appears in two or more contiguous ECG leads, reflecting a single region of heart tissue undergoing transmural ischemia. This pattern is why the diagnosis of STEMI hinges on seeing ST elevation across adjacent leads that look at the same territory—for example, inferior involvement in II, III, and aVF, or anterior involvement in V1–V4. A single lead showing ST elevation does not meet the criteria, because it could be a partial or non-diagnostic finding and might be seen with artifact or nonischemic conditions. ST elevation in aVR can occur with wide, diffuse ischemia or with proximal occlusion of the left coronary system and is not the classic STEMI pattern on its own. ST depression in the inferior leads (II, III, aVF) often represents reciprocal changes associated with an inferior MI, not a standalone STEMI criterion. So, the most clinically meaningful indicator of an acute MI on ECG is ST elevation in two or more contiguous leads, pointing to a regional, transmural injury that requires urgent reperfusion.