A 68-year-old man with chronic left bundle branch block presents with 40 minutes of chest pain. Which ECG finding would support a diagnosis of acute myocardial infarction in this patient?
- A ST depression of 0.5 mm in lead V2
- B Discordant ST elevation of 3 mm in lead V1
- C Concordant ST elevation of 1.5 mm in lead V5 ✓
- D QS complexes in leads V1 to V3
Correct answer: C. Concordant ST elevation of 1.5 mm in lead V5
Explanation
By the Sgarbossa criteria, concordant ST elevation of at least 1 mm in a lead with a positive QRS complex carries the highest weight (score 5) and strongly suggests acute MI in LBBB. Concordant ST depression of at least 1 mm in V1-V3 also counts, but 0.5 mm does not. Discordant ST elevation must exceed 25 percent of the S wave depth to be significant. QS complexes in V1-V3 are expected in uncomplicated LBBB.
Reference: Braunwald's Heart Disease, 12th ed.
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