✅ What is the Modified Sgarbossa Criteria

Following are some good references for the Modified Sgarbossa Criteria (MSC) for diagnosing myocardial infarction in the presence of wide QRS (e.g. Left Bundle Branch Block — LBBB — or paced rhythm):

✅ What is the Modified Sgarbossa Criteria

The Modified Sgarbossa Criteria was proposed by Stephen W. Smith et al (2012) to improve the diagnostic accuracy of the original Sgarbossa Criteria in patients with LBBB or ventricular paced rhythm. 

The key modification is replacing the “absolute ST-elevation ≥ 5 mm in a lead with a negative (discordant) QRS” rule with a proportional rule based on the ST-segment to S-wave amplitude ratio (ST/S ratio). 

Using a proportional cutoff (e.g. ST/S ≤ –0.25, or ST elevation ≥ 25% of the depth of the S wave) improves sensitivity compared with the original fixed-mm rule, while maintaining high specificity. 

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📚 Key Literature / References

Reference / Source Notes / Findings

Smith SW, Dodd KW, Henry TD, Dvorak DM, Pearce LA. “Diagnosis of ST-elevation myocardial infarction in the presence of left bundle branch block with the ST-elevation to S-wave ratio in a modified Sgarbossa rule.” Ann Emerg Med. 2012;60(6):766–76. Original description of MSC, introducing ST/S-ratio rule. 

“Real-time validation of the Sgarbossa and modified Sgarbossa criteria in intermittent left bundle branch block.” Journal of Electrocardiology. 2020;63:24–27. Prospective “real-time” validation showing MSC useful even in intermittent LBBB. 

“Performance characteristics of the modified Sgarbossa criteria for diagnosis of acute coronary occlusion in ED patients with ventricular paced rhythm.” (PERFECT study) Can J Emerg Med. 2018. Demonstrated MSC’s higher sensitivity vs original Sgarbossa in paced rhythms. 

Case report: “Electrocardiographic diagnosis of acute myocardial infarction in a pacemaker patient” BMC Cardiovascular Disorders, 2022. Illustrates a real-world case where original criteria failed but MSC flagged MI. 

Educational overviews / ECG-teaching sites (e.g. “Left bundle branch block (LBBB) in acute MI: Sgarbossa & modified Sgarbossa”). Good for visual aids, ECG examples, step-by-step application of MSC. 

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🧠 Summary of MSC Rules

Under MSC, the ECG is considered positive if any one of the following is present (in a patient with LBBB or paced rhythm plus appropriate clinical presentation):

1. Concordant ST-segment elevation ≥ 1 mm in a lead with a predominantly positive QRS complex. 

2. Concordant ST-segment depression ≥ 1 mm in leads V1, V2, or V3. 

3. Excessively discordant ST-segment elevation, defined as ST elevation ≥ 1 mm and ST-segment to S-wave (ST/S) amplitude ratio ≤ –0.25 (i.e., ST elevation ≥ 25% of the S-wave depth). 

> Note: This proportional rule replaces the fixed “>5 mm” rule from original Sgarbossa, which was often too blunt, resulting in under-diagnosis. 

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⚠️ Limitations & Practical Caveats

Even with MSC, a significant portion of patients with acute myocardial infarction in the context of LBBB or paced rhythm may have no ECG meeting these criteria. Clinical judgment + biomarkers + imaging remain essential. 

Application requires accurate measurement of ST-segment and S-wave amplitudes (often using calipers), and understanding of “concordance” vs “discordance” in the context of wide QRS.