A 58-year-old man with diabetes and hypertension presents to the emergency department with acute-onset substernal chest pain radiating to the back, diaphoresis, and dyspnea for 2 hours. His 12-lead ECG shows the pattern marked **A** in the diagram: horizontal ST depression (1.2 mm) with tall upright R-waves (R/S ratio 1.5 in V2) and upright T-waves in leads V1–V3. Troponin I is elevated at 2.8 ng/mL. Which of the following is the most appropriate IMMEDIATE next step in management?

Explanation

## Why option 1 is correct The pattern marked **A** — horizontal ST depression with tall upright R-waves and upright T-waves in V1–V3 — is the mirror-image ECG manifestation of **posterior wall ST-elevation myocardial infarction (posterior STEMI)**. Although the standard 12-lead ECG has no direct leads viewing the posterior wall, this reciprocal pattern is pathognomonic for acute posterior infarction. The posterior wall is supplied by the posterior descending artery (PDA), usually from the right coronary artery (RCA) in right-dominant circulation (~85%). **Posterior STEMI is a true STEMI and meets reperfusion criteria.** The immediate next step is to obtain **posterior leads V7, V8, V9** (placed at the left posterior axillary line, left scapular tip, and left paraspinal region at the same horizontal level as V6) to confirm ST elevation ≥0.5 mm in the posterior leads, which definitively establishes posterior STEMI. Once confirmed, the patient requires **urgent reperfusion: primary PCI within 90–120 minutes door-to-balloon time (preferred) or thrombolysis within 30 minutes door-to-needle** if PCI is unavailable. This patient should receive dual antiplatelet therapy (aspirin 325 mg chewed + P2Y12 inhibitor loading dose), anticoagulation (unfractionated heparin or enoxaparin), and high-dose statin. Posterior STEMI is frequently under-recognized, leading to missed reperfusion and worse outcomes; timely recognition and treatment are critical. ## Why each distractor is wrong - **Option 2**: ST depression in V1–V3 with tall R-waves and upright T-waves is NOT subendocardial ischemia (which presents with diffuse, downsloping ST depression across many leads, often with ST elevation in aVR, and requires only conservative management). This is the mirror image of posterior STEMI and is a true STEMI requiring urgent reperfusion, not observation. Serial troponins and watchful waiting will result in missed reperfusion and myocardial necrosis. - **Option 3**: Nitrates are contraindicated in posterior STEMI if right ventricular (RV) infarction coexists (common with RCA occlusion causing inferoposterior MI), because RV infarction is preload-dependent and nitrates cause dangerous hypotension. Moreover, delaying reperfusion therapy by 30 minutes for a repeat ECG is inappropriate when the diagnosis is already established by the mirror-image pattern and elevated troponin; reperfusion must begin immediately after posterior leads confirm the diagnosis. - **Option 4**: Echocardiography is useful for assessing wall motion abnormalities and ruling out mechanical complications (e.g., papillary muscle rupture, VSD) in the post-reperfusion period, but it should NOT delay urgent reperfusion therapy. The diagnosis is already established by ECG and troponin; echo is a secondary investigation. **High-Yield:** Posterior STEMI = ST depression + tall R-waves + upright T-waves in V1–V3 (mirror image). Confirm with posterior leads V7–V9, then reperfuse urgently — it is a true STEMI, not NSTEMI. [cite: Harrison 21e Ch 269; Braunwald 12e Ch 59]