The patient reports sudden-onset crushing substernal chest pain with radiation to the left arm, onset 45 minutes ago. ECG shows ST elevation of 2mm in leads II, III, and aVF, satisfying the AHA criterion of elevation in two or more contiguous leads. Serum troponin I is 2.8 ng/mL against an institutional upper limit of normal of 0.04 ng/mL, confirming acute myocardial injury. The three independent STEMI diagnostic criteria are each satisfied: characteristic symptoms, qualifying ECG changes, and elevated cardiac biomarkers. Therefore, the diagnosis is inferior STEMI and the patient meets the Class I indication for emergent primary PCI via catheterization lab activation.