What are the Sagarbossa criteria for diagnosing acute myocardial infarction (AMI) based on electrocardiogram (ECG) findings?

Sgarbossa Criteria for Diagnosing Acute Myocardial Infarction

The Sgarbossa criteria are a validated set of electrocardiographic findings used to diagnose acute myocardial infarction (AMI) in patients with left bundle branch block (LBBB) or ventricular paced rhythms, with the modified Sgarbossa criteria showing superior diagnostic performance with 91% sensitivity and 90% specificity.

Original Sgarbossa Criteria

The original Sgarbossa criteria include three ECG findings that are independently predictive of AMI in patients with LBBB 1:

1. ST-segment elevation ≥1 mm concordant with the QRS complex (sensitivity 73%, specificity 92%)
2. ST-segment depression ≥1 mm in leads V1-V3 (sensitivity 25%, specificity 96%)
3. ST-segment elevation ≥5 mm discordant with the QRS complex (sensitivity 19%, specificity 82%)

These criteria were developed from the GUSTO-I trial and have been validated in multiple studies. They help overcome the challenge of diagnosing AMI in patients with LBBB, where the normal ECG pattern shows discordant ST-segment and T-wave changes (opposite direction from the main QRS deflection) 1.

Modified Sgarbossa Criteria

The modified Sgarbossa criteria replace the third criterion with a proportional measurement that significantly improves sensitivity while maintaining high specificity 2:

1. ST-segment elevation ≥1 mm concordant with the QRS complex in any lead
2. ST-segment depression ≥1 mm in leads V1-V3
3. ST/S ratio ≤-0.25 in leads with discordant ST elevation (replaces the fixed 5 mm threshold)

The modified criteria have shown superior diagnostic performance with a sensitivity of 91%, specificity of 90%, and positive likelihood ratio of 9.0 2, 3.

Application in Clinical Practice

When evaluating a patient with LBBB or ventricular paced rhythm and suspected AMI:

1. Obtain a 12-lead ECG immediately
2. Apply the modified Sgarbossa criteria:
   • Look for concordant ST elevation ≥1 mm in any lead
   • Check for ST depression ≥1 mm in leads V1-V3
   • Calculate ST/S ratio in leads with discordant ST elevation (ratio ≤-0.25 is positive)
3. If any criterion is positive, activate cardiac catheterization lab immediately
4. If criteria are negative but clinical suspicion remains high, obtain serial ECGs, check cardiac biomarkers (troponin), and consider urgent angiography if symptoms persist 2

Limitations and Considerations

• The original Sgarbossa criteria have limited sensitivity (19-73% for individual criteria) but high specificity (82-96%) 1, 4
• Observer variability in interpreting these criteria can be significant, with better agreement for ST depression than for ST elevation patterns 4
• The prevalence of concordant ST elevation in AMI with LBBB is relatively low (6.3%), making this a specific but insensitive finding 4
• The modified criteria significantly improve diagnostic performance, particularly for identifying subtle cases of AMI 3, 5

Application in Ventricular Paced Rhythms

The Sgarbossa criteria have also been validated for ventricular paced rhythms with similar diagnostic characteristics:

• ST-segment elevation ≥5 mm discordant with the QRS complex (sensitivity 53%, specificity 88%)
• ST-segment elevation ≥1 mm concordant with the QRS complex (sensitivity 18%, specificity 94%) 1, 6

The modified criteria are recommended for paced rhythms as well, with any positive criterion warranting urgent cardiac catheterization 2.

Clinical Implications

Early recognition of AMI in patients with LBBB or ventricular paced rhythms is crucial for timely reperfusion therapy. The Sgarbossa criteria, particularly in their modified form, provide a valuable tool for identifying patients who may benefit from early aggressive treatment strategies, potentially improving outcomes in this challenging diagnostic scenario 6, 7.