A 60-year-old diabetic man presents with severe epigastric discomfort and diaphoresis. ECG shows horizontal ST depression in leads V1 through V3 with dominant R waves in those leads and upright, tall T waves. Troponin I is elevated. Which investigation will best confirm the diagnosis?
- A ST-segment monitoring in lead aVR
- B Posterior chest leads V7, V8 and V9 ✓
- C Right-sided chest leads V3R and V4R
- D Coronary CT angiography
Correct answer: B. Posterior chest leads V7, V8 and V9
Explanation
The findings represent acute posterior wall MI, typically from occlusion of the left circumflex or a dominant RCA. Because there are no posterior leads on the standard 12-lead tracing, the injury appears as reciprocal horizontal ST depression with tall R waves and upright T waves in V1-V3, often mistaken for anterior ischemia. Recording leads V7-V9 reveals ST elevation of 0.5 mm or more and confirms true posterior STEMI, making the patient eligible for reperfusion therapy.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.