Modified Sgarbossa: Identifies acute MI in patients with LBBB or Ventricular Paced rhythms.
Concordant ST Elevation ≥ 1mm
ST elevation in a lead with a positive QRS complex (most specific).
Concordant ST Depression ≥ 1mm in V1-V3
ST depression in leads with negative QRS (V1, V2, or V3).
Discordant ST/S ratio ≤ -0.25
Excessive discordance: ST elevation height / S wave depth ≤ -0.25 (Modified Smith criterion).
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
Evaluation of suspected Acute Myocardial Infarction in the presence of LBBB.
Proposed as a more sensitive alternative to the original Sgarbossa criteria.
Section 2
Formula & Logic
Smith’s Modification
The original 3rd Sgarbossa criterion (≥ 5mm discordant ST elevation) was found to be poor at discriminating AMI. Smith modified this to a proportional rule.
The S/T Ratio
ST elevation / S-wave amplitude ≤ −0.25
In other words, discordant ST elevation that is at least 25% of the preceding S-wave depth is considered a positive sign of MI.
Section 3
Pearls/Pitfalls
Sensitivity Boost
The modified criteria increase sensitivity from ~20-30% to ~80% while maintaining high specificity (~99%). It is now widely recommended over the original criteria in emergency medicine.
Section 4
Next Steps
Complementary Calculators
Sgarbossa Criteria
HEART Score (Chest Pain)
GRACE ACS Risk Score
TIMI Risk Score (STEMI)
Killip Classification
Section 5
Evidence Appraisal
Validation Study
Diagnosis of ST-elevation myocardial infarction in the presence of left bundle branch block with the ST-elevation to S-wave ratio in a modified Sgarbossa rule.
Smith SW et al. • Ann Emerg Med.. 2012;60(6):766–76. Validated the −0.25 ratio threshold.
