What are the Sgarbosa criteria?

Sgarbosa Criteria for Diagnosing Acute Myocardial Infarction in Left Bundle Branch Block

The Sgarbosa criteria are three highly specific electrocardiographic findings that identify acute myocardial infarction in patients with left bundle branch block (LBBB), and any patient meeting these criteria requires immediate reperfusion therapy, preferably via emergency coronary angiography with primary PCI. 1

The Three Sgarbosa Criteria

The original Sgarbosa criteria consist of three weighted ECG findings 1:

1. ST-segment elevation ≥1 mm concordant with the QRS complex (sensitivity 73%, specificity 92%) 1

   • This is the most sensitive criterion and carries 5 points in the weighted scoring system 2

2. ST-segment depression ≥1 mm in leads V1-V3 (sensitivity 25%, specificity 96%) 1

   • This finding carries 3 points in the weighted system 2

3. ST-segment elevation ≥5 mm discordant with the QRS complex (sensitivity 19%, specificity 82%) 1

   • This carries 2 points in the weighted system 2

A total score ≥3 points has superb specificity (98%) and positive predictive value for acute myocardial infarction with angiography-confirmed coronary occlusion. 2

Modified Sgarbosa Criteria (Smith Modification)

The third criterion has been refined to improve diagnostic sensitivity 3:

• Replace the absolute ≥5 mm discordant ST elevation with a proportional ST/S ratio ≤-0.25 3
• This modification dramatically increases sensitivity from 52% to 91% while maintaining 90% specificity 3
• The positive likelihood ratio is 9.0 and negative likelihood ratio is 0.1 3
• This unweighted modified rule requires only ONE of the three criteria to be present 3

Clinical Application Algorithm

When encountering a patient with chest pain and LBBB 1, 2:

1. Immediately assess for any of the three Sgarbosa criteria 1

2. If ANY criterion is met:

   • Activate the catheterization laboratory immediately 1, 4
   • Proceed to emergency coronary angiography with intent for primary PCI 1
   • If PCI cannot be performed within 90 minutes of first medical contact, administer fibrinolytic therapy (especially if symptom onset <3 hours) 1

3. If NO criteria are met:

   • Obtain serial ECGs to demonstrate evolving ischemia 1
   • Do not automatically treat as STEMI equivalent based solely on "new or presumably new LBBB" 2

Physiologic Basis

Understanding normal LBBB patterns is critical to recognizing pathologic changes 1:

• Leads with predominantly negative QRS complexes (QS or rS) normally show ST elevation and prominent positive T waves 1
• Leads with large monophasic R waves normally show ST depression and inverted T waves 1
• Loss of this normal discordance (i.e., concordance) indicates myocardial injury or ischemia 1

Extension to Ventricular Paced Rhythms

The Sgarbosa criteria have been validated in patients with ventricular pacing 1:

• ST elevation ≥5 mm discordant with QRS: sensitivity 53%, specificity 88% 1
• ST elevation ≥1 mm concordant with QRS: sensitivity 18%, specificity 94% 1
• ST depression ≥1 mm in V1-V3: sensitivity 29%, specificity 82% 1

Critical Pitfalls to Avoid

The 2004 STEMI guideline recommendation to treat all "new or presumably new LBBB" as STEMI equivalent led to excessive false catheterization laboratory activations and inappropriate fibrinolytic therapy, as most such patients do not have acute coronary occlusion. 2

The 2013 STEMI guideline removed this recommendation entirely, but this creates the opposite problem of potentially denying reperfusion to high-risk patients who DO have acute occlusion. 2

The solution is mandatory use of Sgarbosa criteria to accurately identify which LBBB patients require emergent reperfusion 2:

• High specificity (98%) prevents false activations 2
• The modified criteria with ST/S ratio improve sensitivity to 91%, reducing missed diagnoses 3
• Real-time validation has confirmed these criteria accurately track dynamic ST changes 5

Measurement Technique

For the modified Sgarbosa criteria 3:

• Measure the R or S wave (whichever is most prominent) and ST segments relative to the PR segment to the nearest 0.5 mm 3
• Calculate the ST/S ratio for each lead with both discordant ST deviation ≥1 mm and an R or S wave of opposite polarity 3
• Use the most negative ST/S ratio; if it is ≤-0.25, the criterion is met 3