CFM Cardiology Practice Test 2026 – The Comprehensive All-in-One Guide to Exam Success!

In left bundle branch block (or paced rhythm), ST-T changes can be misleading, so we use Sgarbossa criteria to spot real ischemia. The most specific pattern described is discordant ST-segment elevation that is greater than 25% of the depth of the preceding S wave in the same lead. In other words, if the QRS has a large S wave and the ST segment rises significantly opposite to that QRS deflection—more than quarter of the S wave height—that pattern strongly suggests an acute myocardial infarction rather than just the abnormal repolarization from the block. This is why the option describing discordant ST elevation exceeding 25% of the S wave is the correct Sgarbossa criterion.

For context, other recognized patterns include concordant ST elevation (ST elevation in the same direction as the QRS, typically ≥1 mm) and ST depression of ≥1 mm in leads V1–V3, but the specific option highlighted matches the classic discordant-25% rule most closely.