What are the Sgarbossa criteria (Electrocardiogram criteria) for diagnosing acute myocardial infarction (AMI) in patients with left bundle branch block (LBBB) or paced rhythms?

Sgarbossa Criteria for Diagnosing AMI in LBBB and Paced Rhythms

The Sgarbossa criteria consist of three highly specific electrocardiographic findings that identify acute myocardial infarction in patients with left bundle branch block or ventricular paced rhythms, enabling immediate reperfusion therapy decisions. 1

The Three Sgarbossa Criteria

The original criteria derived from the GUSTO-I trial include:

1. ST-segment elevation ≥1 mm concordant with the QRS complex (sensitivity 73%, specificity 92%) 2, 1

   • This means ST elevation occurs in the same direction as the predominant QRS deflection
   • This is the most sensitive of the three criteria 2

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

   • These leads typically show dominant S waves in LBBB
   • This represents concordant ST changes and has the highest specificity 2

3. ST-segment elevation ≥5 mm discordant with the QRS complex (sensitivity 19%, specificity 82%) 2, 1

   • This means excessive ST elevation opposite to the QRS direction
   • Recent evidence suggests this criterion has very low specificity and sensitivity 2

Scoring System and Clinical Application

A Sgarbossa score ≥3 points has 98% specificity and excellent positive predictive value for acute coronary occlusion, making it the threshold for immediate reperfusion therapy. 3, 4

• Each criterion is assigned points based on its diagnostic weight 3
• Patients meeting any criterion (score ≥3) should receive immediate reperfusion therapy 2, 1, 5
• Higher scores correlate with increased mortality: 23.5% vs 7.7% at 30 days for scores ≥3 vs <3 3

Physiologic Rationale

The criteria exploit the normal discordance pattern in LBBB: 2, 1

• Leads with predominantly negative QRS complexes normally show ST elevation and positive T waves 2
• Leads with large monophasic R waves normally show ST depression and inverted T waves 2
• Loss of this normal discordance (concordance) indicates myocardial injury or ischemia 2, 1

Application to Ventricular Paced Rhythms

The Sgarbossa criteria have been validated in ventricular paced rhythms with similar performance: 2, 6, 7

• ST elevation ≥5 mm discordant with QRS (sensitivity 53%, specificity 88%) 2, 1
• ST elevation ≥1 mm concordant with QRS (sensitivity 18%, specificity 94%) 2, 1
• ST depression ≥1 mm in V1-V3 (sensitivity 29%, specificity 82%) 2, 1

Treatment Algorithm Based on Sgarbossa Criteria

For patients with LBBB or paced rhythm meeting Sgarbossa criteria: 5

1. If symptom onset <3 hours: Administer fibrinolytic therapy if PCI cannot be performed within 90 minutes of first medical contact (Level B recommendation) 2, 5

2. If symptom onset 3-6 hours in high-risk patients: Administer fibrinolytic therapy if PCI balloon time >90 minutes (Level C recommendation) 2, 5

3. Preferred strategy: Emergency cardiac catheterization with primary PCI when available 1, 5

4. If criteria not met: Perform serial ECGs to detect evolving ischemia 2, 1

Critical Clinical Pitfalls

The major limitation is low sensitivity (individual criteria range 19-73%), meaning many AMIs will be missed if relying solely on these criteria. 2, 1

• Patients not meeting criteria may still have AMI and require serial ECGs and troponin monitoring 2, 1
• The 2013 STEMI guideline removed "new or presumably new LBBB" as a STEMI equivalent, which could deny reperfusion to high-risk patients 4
• False catheterization laboratory activation occurs when applying overly broad criteria without Sgarbossa scoring 4
• The high specificity (>90%) means positive criteria strongly indicate AMI and warrant immediate action 2, 4

Modified Sgarbossa Criteria

The Smith-modified Sgarbossa criteria have been developed to improve sensitivity while maintaining specificity, particularly for the discordant ST elevation criterion, though this modification requires further validation in paced rhythms 8, 7