What are the Sgarbossa 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 or Paced Rhythms

The Sgarbossa criteria are the most validated tool for diagnosing acute myocardial infarction (AMI) in patients with left bundle branch block (LBBB) or paced rhythms, with a score ≥3 having high specificity (98%) for acute coronary occlusion. 1

Original Sgarbossa Criteria

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

1. ST-segment elevation ≥1 mm and concordant with the QRS complex (5 points)

   • Sensitivity: 73%, Specificity: 92% 2

2. ST-segment depression ≥1 mm in leads V1-V3 (3 points)

   • Sensitivity: 25%, Specificity: 96% 2

3. ST-segment elevation ≥5 mm and discordant with the QRS complex (2 points)

   • Sensitivity: 19%, Specificity: 82% 2

A total score of ≥3 is considered diagnostic for AMI in the setting of LBBB.

Application to Paced Rhythms

The Sgarbossa criteria have also been validated in patients with ventricular paced rhythms, with similar findings:

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

Modified Sgarbossa Criteria (Smith-Modified)

The Smith-modified Sgarbossa criteria replace the third criterion with:

• ST elevation/S wave ratio ≤ -0.25 in at least one lead 3

This modification improves diagnostic accuracy by accounting for QRS amplitude.

Clinical Significance and Validation

The Sgarbossa criteria have been validated in large clinical trials:

• In the ASSENT 2 & 3 trials, 48.7% of LBBB patients with elevated cardiac enzymes had a Sgarbossa score ≥3, compared to only 12.6% of those without enzyme elevation (p<0.001) 4
• Patients with Sgarbossa scores ≥3 had significantly higher mortality (23.5% vs 7.7% at 30 days, p<0.001) 4

Limitations

1. Observer variability: Agreement between interpreters ranges from fair to moderate, with better agreement for ST depression than for ST elevation criteria 5

2. Low sensitivity: While highly specific, the criteria have limited sensitivity, potentially missing some cases of AMI 5

3. Prevalence: Concordant ST changes are infrequently seen in AMI (concordant ST elevation: 6.3%, concordant ST depression: 3.1%) 5

Clinical Algorithm for Suspected AMI with LBBB or Paced Rhythm

1. Apply Sgarbossa criteria to the ECG
2. If score ≥3, treat as STEMI equivalent and consider urgent reperfusion therapy
3. If score <3 but clinical suspicion remains high:
   • Obtain serial ECGs to detect evolving changes
   • Measure cardiac biomarkers (preferably troponin)
   • Consider additional imaging (echocardiography to assess wall motion)

Importance in Current Practice

Despite the 2013 STEMI guidelines removing LBBB as an automatic STEMI equivalent, the Sgarbossa criteria remain crucial for identifying true STEMIs in this population. Failing to recognize these patients could deny them potentially life-saving reperfusion therapy 1.

The criteria provide a practical approach to risk-stratify this diagnostically challenging high-risk group and optimize the risk-benefit ratio of acute therapy 4.