Which ECG finding is indicative of an acute STEMI?

• A. ST-segment elevation in contiguous leads, with possible reciprocal changes; new left bundle branch block can also indicate STEMI.
• B. ST-segment depression in multiple leads.
• C. Prolonged QT interval with flattened T waves.
• D. Delta wave with short PR.

Answer: (B)

ST-segment elevation in contiguous leads signals acute STEMI because it shows transmural (full-thickness) myocardial injury in the region served by the occluded coronary artery. The ECG leads that view the same anatomical area will lift the ST segment together, and you may also see reciprocal ST-segment depression in opposite leads. A new left bundle branch block can also indicate STEMI when it occurs in the appropriate clinical setting, since the LBBB can mask subtle ST changes and is treated as a STEMI equivalent.

ST-segment depression in multiple leads is not the hallmark of an acute STEMI; it more often points to subendocardial ischemia, NSTEMI, or diffuse ischemia, and may be a reciprocal finding in certain posterior infarctions. Prolonged QT with flattened T waves points to electrolyte disturbances or other non-STEMI processes, and a delta wave with a short PR interval indicates preexcitation (Wolff-Parkinson-White) rather than an acute STEMI.