Modified Sgarbossa Criteria

Why use it

LBBB affects approximately 0.1–0.5% of the general population and is present in 4–7% of AMI patients at presentation. The presence of LBBB with new or presumed new onset historically triggered automatic primary PCI activation (Sgarbossa 1996 era), but this led to significant over-activation of cath labs (~50% false-positive rate). The Modified Sgarbossa Criteria (Smith 2012) provide a more accurate and nuanced framework for identifying true AMI in LBBB or ventricular paced rhythm, reducing unnecessary activations while improving sensitivity for genuine STEMIs. Any patient with even one positive Sgarbossa criterion should be evaluated urgently in a cardiac context.

About

The Sgarbossa Criteria were developed by Elena Sgarbossa and colleagues and published in the New England Journal of Medicine in 1996, derived from the GUSTO-1 trial (n=26,003), to diagnose acute myocardial infarction (AMI) in patients with left bundle branch block (LBBB). LBBB distorts the ST segment and T wave morphology, making the standard STEMI criteria inapplicable — historically leading to underdiagnosis of AMI in LBBB patients. The original criteria identify three ECG patterns associated with AMI in LBBB, each assigned a weighted score: (1) concordant ST elevation ≥1 mm in any lead with a positive QRS complex (5 points — highest specificity ~94%); (2) concordant ST depression ≥1 mm in leads V1, V2, or V3 (3 points); (3) discordant ST elevation ≥5 mm in any lead with a negative QRS complex (2 points — most sensitive but least specific). A total score ≥3 historically indicated AMI with high specificity. Stephen Smith and colleagues (2012) subsequently published a crucial modification: replacing criterion 3 (discordant ST elevation ≥5 mm absolute) with a proportional criterion — ST/S ratio ≤ −0.25 (i.e., the ST elevation comprises ≥25% of the absolute magnitude of the preceding S wave). This modification, validated in the Emergency Medicine Journal (2012), dramatically improved sensitivity from 52% to 91% for the discordant criterion while maintaining high specificity, substantially improving overall AMI detection in LBBB patients. The Modified Sgarbossa Criteria are now incorporated into major cardiology guidelines and are the preferred approach for ECG interpretation in LBBB with suspected ACS.

When to use

• Acute chest pain or equivalent ACS symptoms in a patient with known or new LBBB on ECG
• Acute chest pain in a patient with a ventricular paced rhythm (paced rhythms create similar discordant ST-T morphology)
• Any suspected ACS presentation where the baseline ECG shows LBBB — apply criteria to identify concordant or proportionally discordant ST changes
• Emergency evaluation of LBBB in the context of elevated troponin, hemodynamic instability, or clinical features of acute coronary syndrome
• New LBBB in the context of acute symptoms should be presumed ischemic until proven otherwise (Sgarbossa criteria help refine this)

Formula

Pearls & pitfalls

• CONCORDANT means the ST deviation is in the SAME direction as the QRS complex (e.g., ST elevation in a lead where the QRS is predominantly positive, or ST depression in a lead where QRS is predominantly negative). In LBBB, ST-T changes are normally DISCORDANT (opposite to QRS direction) — any concordant change is abnormal and strongly suggests AMI.
• Criterion 1 (concordant STE ≥1 mm) has the highest specificity for AMI (~94%) but lowest sensitivity. Even a single positive criterion should prompt urgent evaluation.
• Criterion 3 using the Smith proportional modification (ST/S ratio ≤ −0.25): measure the ST elevation amplitude in the discordant lead (in mm) and divide by the absolute height of the S wave in the SAME lead (in mm). A ratio ≤ −0.25 (i.e., ≥25% of S amplitude) is positive. This is calculated as: ST elevation / |S wave| — if the result is ≤ −0.25, the criterion is met.
• The Smith modification improved sensitivity for discordant excessive ST elevation from 52% to 91% while maintaining good specificity — it replaces the absolute 5 mm threshold with a proportional one.
• These criteria apply to ventricular PACED rhythms as well as LBBB — both create discordant ST morphology by the same mechanism (altered ventricular activation).
• New LBBB in the context of chest pain was formerly an automatic STEMI equivalent in guidelines (2000s era). Current ACC/AHA guidelines (2022) state that LBBB alone no longer mandates automatic catheterization lab activation — apply Sgarbossa criteria and clinical context.
• A completely NORMAL ECG in LBBB (i.e., all discordant ST-T changes, no concordance, no excessive proportional discordant changes) makes AMI LESS likely but does not exclude it — serial troponins and ECGs are essential.
• The specificity of concordant STE ≥1 mm is so high (~94%) that some authors argue a single positive lead is sufficient to activate the cath lab in an appropriate clinical context.
• Sgarbossa criteria do NOT apply to RBBB — RBBB does not alter left ventricular ST segments in the same way.

Next steps

Any positive criterion (score ≥1 or positive Smith modification): Urgent cardiology consultation and consideration of emergency coronary angiography. Do not delay for serial ECGs if the patient is hemodynamically unstable. Activate PCI protocol per local STEMI pathway. Score 0 (all criteria negative): AMI cannot be excluded on ECG criteria alone. Serial ECGs every 15–30 minutes. Serial high-sensitivity troponin. Clinical assessment and risk stratification. Consider urgent echocardiography for wall motion abnormality. Smith modification positive alone (ST/S ≤ −0.25 without meeting original criterion 3): Treat as strongly positive — sensitivity for AMI ~91%; urgent coronary angiography warranted if clinical picture is consistent.

Evidence

Sgarbossa EB 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. PMID:8559200. Derivation: GUSTO-1 trial substudy (n=26,003). Smith SW et al. Electrocardiographic differentiation of early repolarization from subtle anterior ST-elevation MI. Ann Emerg Med. 2012;60(1):45-56.e2. Smith SW et al. Modified Sgarbossa criteria (ST/S ratio ≤ −0.25): sensitivity 91%, specificity 90% vs original criterion 3 sensitivity 52%, specificity 98%. Di Marco A et al. Clinical validation of the modified Sgarbossa criteria for diagnosis of AMI in the presence of LBBB. Heart. 2017.

References

1. Sgarbossa EB 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. — link
2. Smith SW et al. Electrocardiographic differentiation of early repolarization from subtle anterior ST-elevation MI using the ST-elevation ratio of the T-wave amplitude. Ann Emerg Med. 2012;60(1):45-56. — link
3. Di Marco A et al. Clinical validation of the modified Sgarbossa criteria for diagnosis of AMI in LBBB. Heart. 2017;103(17):1368-1374. — link
4. O'Gara PT et al. 2013 ACCF/AHA Guideline for the Management of ST-Elevation Myocardial Infarction. Circulation. 2013;127(4):e362-425. — link
5. Neeland IJ et al. Electrocardiographic diagnosis of evolving acute MI in the presence of left bundle branch block using the Sgarbossa criteria. J Am Coll Cardiol. 2012;60(16):1511-1521. — link