What are the standard ECG criteria for diagnosing STEMI?

• A. ST-segment depression of ≥2 mm in multiple leads with chest pain lasting >20 minutes.
• B. T-wave inversion in multiple leads with normal troponin.
• C. ST-segment elevation in two contiguous limb leads ≥1 mm or in two contiguous precordial leads ≥2 mm, with ischemic symptoms; reciprocal changes support diagnosis; a new left bundle branch block may obscure.
• D. Any ST elevation in a single lead qualifies STEMI.

Answer: (C)

STEMI is diagnosed on ECG by signs of acute transmural injury: ST-segment elevation at the J point in two contiguous leads. The standard thresholds are at least 1 mm of elevation in limb leads or at least 2 mm in precordial leads, in the setting of ischemic chest pain or equivalent symptoms. Elevation must be in two neighboring leads that reflect the same region of the heart. Reciprocal ST changes in opposite leads can support the diagnosis, and a new left bundle branch block can mask or mimic STEMI, making the diagnosis more complex. This combination—two contiguous leads with the specified elevation plus ischemic symptoms and potential reciprocal changes—is the established criterion for STEMI. The other patterns described (ST depression with chest pain, T-wave inversions with normal troponin, or ST elevation in a single lead) do not meet the diagnostic criteria for STEMI.