Which ECG finding is most indicative of an acute STEMI?

• A. Prolonged PR interval
• B. Hyperkalemia pattern
• C. ST-segment elevation in contiguous leads
• D. QT shortening

Answer: (C)

ST-segment elevation in contiguous leads signals acute transmural injury from a coronary occlusion, which is the hallmark of a STEMI. This pattern shows that a substantial portion of the heart muscle is currently infarcting and needs urgent reperfusion. The ST elevations appear in the leads that view the affected region and may have reciprocal ST depression in opposite leads.

Other ECG patterns described are not typical of an acute STEMI: a prolonged PR interval points to conduction delay rather than infarction; hyperkalemia produces tall, peaked T waves and QRS widening; QT shortening occurs with other metabolic states like hypercalcemia. Hence, ST-segment elevation in contiguous leads is the most specific indicator of an acute STEMI.