A 68-year-old man with known left bundle branch block presents with 1 hour of chest pain. His ECG shows concordant ST elevation of 3 mm in lead V5, concordant ST depression of 2 mm in V2, and excessive discordant ST elevation of 7 mm in V3 relative to the S-wave depth. Which feature carries the highest diagnostic weight for acute MI by the modified Sgarbossa criteria?

• A Concordant ST depression of 2 mm in V2
• B Concordant ST elevation of 3 mm in V5 ✓
• C Excessive discordant ST elevation of 7 mm in V3
• D Any ST segment change in more than two contiguous leads

Explanation

In the modified Sgarbossa criteria, concordant ST elevation of 1 mm or more in a lead with a positive QRS remains the most specific single sign of occlusion MI in LBBB. Concordant ST depression of 1 mm or more in V1 to V3 is also specific but slightly less weighted. Excessive discordant elevation needs an ST/S ratio of 0.25 or more, so 7 mm qualifies only if the S wave is under 28 mm, whereas concordant elevation stands alone.

Reference: Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 12th ed.

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