Smith's version: replaces the 3rd criterion with the ST/S ratio. Check the findings present: any positive criterion indicates MI.
Criteria checked0 of 3
Modified Sgarbossa negative
Nondiagnostic
No positive criteria.
Decision rule
Any positive criterion → MI with LBBB / paced rhythm.
A tool to support learning and decision-making. The result does not replace clinical evaluation of the patient.
About: Modified Sgarbossa criteria
Left bundle branch block and paced rhythm alter the ST segment and make infarction harder to diagnose. The 1996 Sgarbossa criteria identify changes that secondary repolarization does not explain.
In Smith's modified version (2012), the third criterion (discordant ST elevation ≥ 5 mm) was replaced by a proportional ratio between the ST segment and the S or R wave, which increased sensitivity for coronary occlusion.
How to use
Look for concordant ST elevation (in the same direction as the QRS) ≥ 1 mm in any lead.
Look for concordant ST depression ≥ 1 mm in V1, V2 or V3.
In leads with discordant ST, calculate the ST/S (or ST/R) ratio: ≥ 25% of the opposite wave is positive.
How to interpret
Any positive criterion: consistent with acute infarction in the presence of LBBB or a paced rhythm.
No criteria: nondiagnostic; the clinical picture, its course and cardiac biomarkers remain decisive.
Limitations
Negative criteria do not rule out coronary occlusion. In a patient with suggestive chest pain and instability, discuss reperfusion even without a positive criterion.
References
Sgarbossa EB, Pinski SL, Barbagelata A, et al. Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. N Engl J Med. 1996;334(8):481–7.
Smith SW, Dodd KW, Henry TD, Dvorak DM, Pearce LA. 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. Ann Emerg Med. 2012;60(6):766–76.
