What ECG change indicates an acute STEMI in the leads overlying the infarct?

• A. T wave inversions in the inferior leads
• B. Q waves develop in the infarcted region early
• C. ST-segment elevation in the affected leads with reciprocal ST depression in opposite leads
• D. ST-segment depression in all leads

Answer: (C)

Acute STEMI shows ST-segment elevation in the ECG leads that overlie the area of infarction, reflecting transmural injury. The current of injury during the acute phase elevates the ST segment (at the J point) in those leads. Because the electrical vector of injury points toward the affected region, leads facing away from it exhibit reciprocal ST-segment depression. This combination—local ST elevation with reciprocal depression in opposite leads—best indicates an acute STEMI and signals urgent reperfusion needs.

T wave inversions can occur with ischemia or evolving infarction but are not the definitive early sign of an acute STEMI. Q waves signify established necrosis rather than an acute event. ST-segment depression in all leads isn’t the characteristic pattern for an acute STEMI.