In an adult with chest pain and a left bundle‑branch block or ventricular‑paced rhythm on ECG, what are the original and modified Sgarbossa criteria and how are they applied to diagnose an acute myocardial infarction?

Sgarbossa Criteria for Diagnosing Acute Myocardial Infarction in Left Bundle Branch Block and Ventricular Paced Rhythm

Original Sgarbossa Criteria

The original Sgarbossa criteria consist of three independent ECG findings that predict acute myocardial infarction in patients with left bundle branch block (LBBB), with a scoring system where ≥3 points indicates high specificity (98%) for acute coronary occlusion. 1, 2

The three criteria with their point values are:

• ST-segment elevation ≥1 mm concordant with the QRS complex (5 points): This finding has sensitivity of 73% and specificity of 92% 1, 2
• ST-segment depression ≥1 mm in leads V1, V2, or V3 (3 points): This demonstrates sensitivity of 25% and specificity of 96% 1, 2
• ST-segment elevation ≥5 mm discordant with the QRS complex (2 points): This has sensitivity of 19% and specificity of 82% 1, 2

Modified Sgarbossa Criteria

The modified Sgarbossa criteria replace the third criterion (excessive discordant ST elevation ≥5 mm) with a proportional criterion: ST-segment elevation at the J-point with amplitude ≥25% of the preceding S-wave depth. 1

This modification improves sensitivity from 19% to 60% while maintaining high specificity of approximately 86% 3

The modified criteria are:

• Concordant ST-segment elevation ≥1 mm in leads with positive QRS complex 1
• Concordant ST-segment depression ≥1 mm in leads V1-V3 1
• ST/S ratio ≥-0.25 (or ≥25%) in leads with discordant ST elevation 1

Application in Ventricular Paced Rhythm

The Sgarbossa criteria apply to ventricular paced rhythms with similar diagnostic accuracy, as paced rhythms create ECG morphology identical to LBBB. 1, 4, 5

In 32 patients with ventricular paced rhythm and AMI from the GUSTO-I trial, the criteria showed:

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

Clinical Application Algorithm

When evaluating chest pain with LBBB or ventricular paced rhythm, apply the modified Sgarbossa criteria immediately upon obtaining the ECG within 10 minutes of first medical contact. 1

Step-by-step approach:

1. If any concordant ST elevation ≥1 mm OR concordant ST depression ≥1 mm in V1-V3 is present: Activate catheterization laboratory immediately for primary PCI with door-to-balloon time ≤90 minutes 6

2. If discordant ST elevation is present: Calculate the ST/S ratio; if ≥-0.25 (meaning ST elevation is at least 25% of the S-wave depth), treat as STEMI equivalent 1

3. If criteria are not met but clinical suspicion remains high: Obtain serial ECGs every 15-30 minutes to detect evolving ischemia, and measure high-sensitivity troponin at presentation and 1-2 hours 1, 6

Understanding the Physiologic Basis

In LBBB, the normal ECG pattern shows QRS-T wave discordance, meaning ST segments and T waves point opposite to the terminal QRS deflection. 1

• Leads with predominantly negative QRS complexes (QS or rS) normally have elevated ST segments and upright T waves 1
• Leads with large monophasic R waves normally show ST depression and inverted T waves 1
• Loss of this expected discordance (concordance) indicates myocardial injury 1

Critical Pitfalls to Avoid

Do not assume all LBBB patients with chest pain have acute MI—the original 2004 guideline recommendation to treat "new or presumably new LBBB" as STEMI equivalent led to excessive false catheterization laboratory activations, as most such patients do not have acute coronary occlusion. 1, 7

However, do not deny reperfusion therapy to patients meeting Sgarbossa criteria, as this represents a high-risk population with confirmed acute coronary occlusion. 7

The 2013 STEMI guideline removed LBBB as a STEMI equivalent precisely because of poor diagnostic accuracy without specific criteria 1, 7

Performance Characteristics in Real-World Practice

In emergency department settings with low OMI prevalence (2.4%), all ECG criteria show low positive predictive values (4.6-9.4%) but excellent negative predictive values (>98%). 3

This means:

• A positive Sgarbossa score strongly suggests OMI and warrants immediate catheterization 3
• A negative score does not exclude OMI and requires serial ECGs, troponin measurement, and clinical correlation 3
• ECG criteria alone are insufficient—integrate with clinical presentation, troponin trends, and echocardiography when available 5, 3

Scoring System for Original Criteria

A total score ≥3 points is required for diagnosis using the original weighted Sgarbossa criteria. 1

For example:

• Concordant ST elevation ≥1 mm alone = 5 points (meets threshold) 1
• Concordant ST depression ≥1 mm in V1-V3 alone = 3 points (meets threshold) 1
• Discordant ST elevation ≥5 mm alone = 2 points (does not meet threshold without additional findings) 1

Treatment Implications

Patients meeting Sgarbossa criteria should receive immediate reperfusion therapy, preferably primary PCI with door-to-balloon time ≤90 minutes. 6

If PCI cannot be achieved within 90 minutes and symptom onset is <3 hours, administer fibrinolytic therapy 1

For high-risk patients presenting <6 hours from symptom onset with expected PCI delay >90 minutes, fibrinolytic therapy is recommended 1