The recognition of ST-segment elevation myocardial infarction (STEMI) in the presence of left bundle-branch block (LBBB) remains difficult and frustrating to both emergency medicine physicians and cardiologists. According to the 2004 STEMI guidelines, emergent reperfusion therapy was recommended to patients with suspected ischemia and new LBBB however, the new 2013 STEMI guidelines made a drastic change by removing this recommendation. Several papers have recently been published discussing a modified Sgarbossa’s criteria and a new algorithm to help decrease false cath lab activation and/or fibrinolytic therapy but, are they ready for primetime?
What were the old LBBB and STEMI activation criteria?
- 1996 and 2004 American College of Cardiology/American Heart Association (ACC/AHA): Class I indication if symptoms < 12 hours  
- 2012 European Society of Cardiology (ESC): Class Ia indication if symptoms < 12 hours 
What are the original Sgarbossa Criteria?
- Concordant ST-segment elevation ≥ 1 mm in any lead = 5 points
- Concordant ST-segment depression ≥ 1 mm in lead V1 – V3 = 3 points
- Discordant ST-segment elevation ≥ 5 mm in any lead = 2 points
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How accurate are the old Sgarbossa Criteria for culprit coronary occlusion on angiography?
- Larson et al: 44% false activation with STEMI and presumed new LBBB 
- Chang et al: 80.8% false activation with STEMI and presumed new LBBB 
- Jain et al: 86% false activation with STEMI and presumed new LBBB 
Ideally, diagnostic tests for life-threatening conditions (i.e. AMI) need to be highly sensitive. The reason the original Sgarbossa criteria are limited in clinical practice is the low sensitivity (i.e. 20%). This is why a new LBBB alone is no longer a criteria for emergent cath lab activation. Recently, Steven Smith, MD from Dr. Smith’s ECG Blog published a new criterion to replace the third component of the original Sgarbossa Criteria using the ST/S ratio instead of discordant ST-elevation ≥ 5mm.
What is the new modified Sgarbossa Criteria?
- Concordant ST-segment elevation ≥ 1 mm in any lead
- Concordant ST-segment depression ≥ 1 mm in lead V1 – V3
- Discordant ST/S Ratio ≤ -0.25
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How should the modified Sgarbossa Criteria be used in initial evaluation of patients with suspected AMI with LBBB? 
- Suspected patient with AMI with LBBB should have emergent primary PCI or fibrinolysis if:
- Hemodynamic instability or acute heart failure (Validated)
- Sgarbossa score ≥ 3 (Validated)
- ST/S ratio ≤ -0.25 (Proposed, NOT Validated)
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What are some limitations of the modified Sgarbossa Criteria and the new algorithm?
- The ST/S ratio study is a very small study (33 vs 129 ECGs)
- More complex, making the modified criteria and algorithm harder to remember
- Need a prospective, externally validated study to confirm clinical application of the modified Sgarbossa Criteria
Take Home Point
The Modified Sgarbossa Criteria is more sensitive than the original Sgarbossa Criteria for predicting AMI in the presence of LBBB, but needs an external validation study before we can begin to apply it.
- Ryan TJ et al. ACC/AHA Guidelines for the Management of Patients with Acute Myocardial Infarction. A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Acute Myocardial Infarction). JACC 1996. PMID: 8890834
- Antman EM et al. ACC/AHA Guidelines for the Management of Patients with ST-elevation Myocardial Infarction; A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Revise the 1999 Guidelines for the Management of Patients with Acute Myocardial Infarction). JACC 2004. PMID: 15358047
- Task Force on the Management of ST-Segment Elevation Acute Myocardial Infarction of the European Society of Cardiology (ESC). ESC Guidelines for the Management of Acute Myocardial Infarction in Patients Presenting with ST-Segment Elevation. Eur Heart J 2012. PMID: 22922416
- Cai Q et al. The Left Bundle-Branch Block Puzzle in the 2013 ST-Elevation Myocardial Infarction Guideline: From Falsely Declaring Emergency to Denying Reperfusion in a High-Risk Population. Are the Sgarbossa Criteria Ready for Prime Time? Am Heart J 2013. PMID: 24016487
- Larson DM et al. “False-Positive” Cardiac Catheterization Laboratory Activation Among Patients with Suspected ST-Segment Elevation Myocardial Infarction. JAMA 2007. PMID: 18165668
- Chang AM et al. Lack of Association Between Left Bundle-Branch Block and Acute Myocardial Infarction in Symptomatic ED Patients. AJEM 2009. PMID: 19857407
- Jain S et al. Utility of Left Bundle Branch Block as a Diagnostic Criterion in Acute Myocardial Infarction. Am J Cardiol 2011. PMID: 21296327
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