Brugada Criteria for Diagnosing STEMI in Left Bundle Branch Block
The Brugada criteria (also known as Sgarbossa criteria) consist of three specific ST-segment patterns that identify acute myocardial infarction in patients with left bundle branch block, with concordant ST elevation being the most reliable finding.
The Three Brugada/Sgarbossa Criteria
The original criteria from the GUSTO-I trial include 1:
- ST-segment elevation ≥1 mm concordant with (in the same direction as) the QRS complex – This is the most specific criterion with the highest positive predictive value 2
- ST-segment depression ≥1 mm in leads V1, V2, or V3 (leads with dominant S waves) – These are concordant changes 1
- ST-segment elevation ≥5 mm discordant with (in the opposite direction from) the QRS complex – This criterion has very low specificity and sensitivity in recent validation studies 1
Performance Characteristics and Clinical Application
Concordant ST-segment changes demonstrate high specificity (98%) but low sensitivity (approximately 20-30%) for acute MI 1, 2. The presence of LBBB with concordant ST elevation is associated with significantly higher 30-day mortality compared to LBBB with enzyme elevation but without concordant changes 1.
The third criterion (discordant ST elevation ≥5 mm) has been shown to have very low specificity and sensitivity in validation studies, limiting its clinical utility 1.
Modified Sgarbossa Criteria (Smith Modification)
A modified version replaces the absolute 5 mm discordant ST elevation threshold with a proportional criterion: ST/S wave ratio ≤-0.25 3. This modification significantly improves sensitivity from 52% to 91% while maintaining 90% specificity 3. The positive likelihood ratio for this modified rule is 9.0, with a negative likelihood ratio of 0.1 3.
However, external validation studies show that even the modified Smith criteria have suboptimal sensitivity (54-67%), meaning 33-46% of patients with true STEMI would not be identified by these criteria alone 4.
Critical Clinical Context
The 2025 ACC/AHA guidelines explicitly state that new or presumably new LBBB at presentation should NOT be considered diagnostic of acute MI in isolation and does not constitute a STEMI equivalent in asymptomatic patients 1. This represents a major shift from older recommendations that treated new LBBB as STEMI-equivalent 5.
The ESC guidelines emphasize that concordant ST elevation in leads with positive QRS deflections remains one of the best indicators of ongoing MI with an occluded infarct artery 1.
Practical Diagnostic Algorithm
When evaluating a patient with chest pain and LBBB 1, 5:
Compare with prior ECGs – Determine if LBBB is new or chronic; new LBBB with ongoing ischemic symptoms warrants urgent evaluation 1
Apply Sgarbossa criteria – Look specifically for concordant ST elevation ≥1 mm or ST depression ≥1 mm in V1-V3 1, 2
Calculate ST/S ratio – In leads with discordant ST elevation ≥1 mm, measure the ratio; ≤-0.25 suggests acute occlusion 3
Assess clinical context – Prolonged chest pain >20 minutes not responding to nitroglycerin strongly supports acute MI regardless of ECG ambiguity 1
Use point-of-care troponin – A positive troponin at 1-2 hours after symptom onset can guide emergency angiography decisions when ECG remains equivocal 1
Proceed to emergency angiography – If clinical suspicion is high and any Sgarbossa criteria are met, proceed directly without waiting for serial biomarkers 1
Common Pitfalls to Avoid
Do not apply standard STEMI voltage criteria to patients with LBBB – The standard thresholds (≥2 mm in V2-V3, ≥1 mm in other leads) were explicitly defined for patients without LBBB and lead to both false positives and false negatives 1, 6, 7.
Do not rely solely on "new LBBB" as a STEMI equivalent – Most patients with suspected ischemia and new LBBB do not have acute coronary occlusion on angiography 5, 4. Clinical correlation is essential 1.
Do not wait for serial troponins if Sgarbossa criteria are positive and clinical presentation is compelling – Patients with STEMI in the setting of LBBB experience significant delays resulting in worse outcomes 6, 7.
Recognize the limitations of all ECG criteria in LBBB – Even the best criteria miss 30-45% of true STEMIs 4, 8. When clinical suspicion remains high despite negative criteria, emergency angiography should be strongly considered 1.
Adjunctive Diagnostic Tools
Serial ECGs should be performed every 10-20 minutes when initial ECG is nondiagnostic but clinical suspicion remains high 1. Dynamic ST changes during ongoing symptoms support the diagnosis of acute MI 7.
Consider additional ECG leads – Record V7-V9 for suspected posterior MI and V3R-V4R for suspected right ventricular involvement 1, 7.