Cardiology
Sgarbossa Criteria
Diagnosing MI in left bundle branch block.
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Background
The Sgarbossa criteria help diagnose acute myocardial infarction (MI) in the presence of left bundle branch block (LBBB) or a ventricular-paced rhythm, where the usual ST-segment criteria for MI are obscured. Three electrocardiographic findings are weighted: concordant ST elevation of at least 1 mm (5 points), concordant ST depression of at least 1 mm in leads V1–V3 (3 points), and discordant ST elevation of at least 5 mm (2 points). The points are summed, and a total of 3 or more is considered specific for acute MI. The criteria exploit ST-segment changes that occur in the same (concordant) or opposite (discordant) direction to the main QRS deflection.
Interpreting the result
A score of 3 or more — achieved by either concordant criterion alone — is highly specific for acute MI in LBBB, meaning a positive result strongly supports the diagnosis. However, the criteria are not sensitive: a score below 3 does not exclude MI, and many true infarcts will score low. The discordant ST-elevation criterion (worth 2 points) is the weakest, and the modified Smith-Sgarbossa rule replaces the fixed 5 mm threshold with a proportional measure (ST/S ratio) to improve sensitivity. The criteria support, but do not replace, the overall clinical and biomarker assessment.
Advice
A score ≥3 is specific (but not sensitive) for acute MI in LBBB. The modified Smith-Sgarbossa criteria improve sensitivity.
Worked example
A patient with known LBBB and chest pain has an ECG showing concordant ST elevation of 2 mm in a lead where the QRS is predominantly positive (5 points). The total is 5, which is 3 or more, and is specific for acute MI — prompting urgent management of a presumed acute coronary occlusion.
Pearls / pitfalls
- A negative result does not rule out MI — the criteria are specific but not sensitive, so clinical suspicion and troponin remain essential.
- The concordant criteria (ST elevation or depression in the same direction as the QRS) are the most powerful; each alone meets the diagnostic threshold.
- Prefer the modified Smith-Sgarbossa rule (proportional ST/S ratio) where the discordant criterion is in question — it improves sensitivity.
- The criteria assume a true LBBB or paced rhythm; ensure the QRS morphology genuinely meets these patterns before applying them.
Evidence & validation
Derived by Sgarbossa and colleagues in 1996 from the GUSTO-1 trial population, the original criteria are specific but limited in sensitivity. The modified Smith-Sgarbossa criteria, using a proportional ST/S ratio, were subsequently shown to improve sensitivity while preserving specificity and are now widely used.
Frequently asked questions
What Sgarbossa score indicates an MI?
A total of 3 or more is considered specific for acute MI in the presence of LBBB. This can be reached by either concordant criterion alone, as concordant ST elevation scores 5 and concordant ST depression scores 3.
Does a low Sgarbossa score rule out MI?
No. The criteria are specific but not sensitive, so a score below 3 does not exclude infarction. Clinical assessment and serial troponin remain essential when suspicion is high.
What are the modified Smith-Sgarbossa criteria?
They replace the fixed discordant ST-elevation threshold of 5 mm with a proportional measure (an ST/S ratio). This improves sensitivity for detecting MI in LBBB while preserving the specificity of the original rule.
Can Sgarbossa criteria be used with paced rhythms?
Yes. They were extended to ventricular-paced rhythms, which produce an LBBB-like pattern. The same concordant and discordant principles apply, although interpretation should remain cautious and clinically informed.
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):481–487.
- Meyers HP, Smith SW, et al. Validation of the modified Sgarbossa criteria (Smith-Sgarbossa) for diagnosis of acute coronary occlusion. Am Heart J. 2015.
About the creator
Sgarbossa EB et al.
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