A 60-year-old diabetic woman presents with epigastric discomfort and diaphoresis. ECG shows horizontal ST depression of 3 mm in leads V1 to V3 with prominent R waves in those leads. Troponin is elevated. In addition to standard ACS management, which additional investigation will best confirm the diagnosis?
- A ST-segment recording from leads V7 to V9 ✓
- B Right-sided precordial leads V3R and V4R
- C Coronary calcium score by CT
- D Repeat ECG after adenosine administration
Correct answer: A. ST-segment recording from leads V7 to V9
Explanation
ST depression in V1 to V3 with dominant R waves suggests posterior ST elevation myocardial infarction, usually from a circumflex occlusion. Recording posterior leads V7 to V9 demonstrates reciprocal ST elevation of 0.5 mm or more and confirms the diagnosis, reclassifying the case as STEMI eligible for reperfusion. Right-sided leads detect right ventricular infarction, not posterior involvement, and calcium scoring has no role in acute diagnosis.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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