Sgarbossa Criteria for AMI in LBBB

The Sgarbossa criteria (Sgarbossa EB et al., NEJM 1996) are ECG criteria for diagnosing acute myocardial infarction in patients with left bundle branch block (LBBB) or a paced rhythm, settings in which standard STEMI criteria do not apply.

There are three criteria: (1) concordant ST elevation ≥1 mm in leads with a positive QRS — 5 points; (2) concordant ST depression ≥1 mm in V1, V2, or V3 — 3 points; (3) discordant ST elevation ≥5 mm in leads with a negative QRS — 2 points. A total score ≥3 has high specificity for AMI (90%).

The modified Smith criteria (2012) replace the third criterion with a proportional one: discordant ST elevation ≥25% of the depth of the preceding S-wave. This markedly improves sensitivity (80% vs 52%) while preserving specificity. Current guidelines, including the ESC 2023 ACS guideline, recommend the modified Smith criteria as the standard.

• Acute chest pain with LBBB on ECG, to diagnose AMI.
• Paced rhythm with suspected ischemia.
• Deciding on reperfusion therapy (thrombolysis vs PCI) in patients with a wide QRS.
• Differentiating old vs new AMI in patients with pre-existing LBBB.

• The sensitivity of the original criteria is low (52%), missing some true AMIs. Use the modified criteria instead.
• In patients with pre-existing LBBB, comparison with a prior ECG is required.
• In a paced rhythm, the criteria are formally applicable but accuracy is lower.
• In intermittent LBBB, interpretation is difficult; assess only during complete block.