- In patients with left bundle branch block (LBBB) or ventricular paced rhythm, infarct diagnosis based on the ECG is difficult.
- The baseline ST segments and T waves tend to be shifted in a discordant direction (“appropriate discordance”), which can mask or mimic acute myocardial infarction.
- However, serial ECGs may show dynamic ST segment changes during ischemia.
- A new LBBB is always pathological and can be a sign of myocardial infarction.
Original Sgarbossa Criteria
The original three criteria used to diagnose infarction in patients with LBBB are:
- Concordant ST elevation > 1mm in leads with a positive QRS complex (score 5)
- Concordant ST depression > 1 mm in V1-V3 (score 3)
- Excessively discordant ST elevation > 5 mm in leads with a negative QRS complex (score 2).
These criteria are specific, but not sensitive for myocardial infarction. A total score of ≥ 3 is reported to have a specificity of 90% for diagnosing myocardial infarction.
During right ventricular pacing the ECG also shows left bundle brach block and the above rules also apply for the diagnosis of myocardial infarction during pacing, however they are less specific.
Modified Sgarbossa Criteria
As discussed in this article by Stephen Smith, modified Sgarbossa criteria have been created to improve diagnostic accuracy. The most important change is the modification of the rule for excessive discordance. The use of a 5 mm cutoff for excessive discordance was arbitrary and non-specific — for example, patients with LBBB and large voltages will commonly have ST deviations > 5 mm in the absence of ischaemia.
The modified rule is positive for STEMI if there is discordant ST elevation with amplitude > 25% of the depth of the preceding S-wave.
Modified Sgarbossa Criteria:
- ≥ 1 lead with ≥1 mm of concordant ST elevation
- ≥ 1 lead of V1-V3 with ≥ 1 mm of concordant ST depression
- ≥ 1 lead anywhere with ≥ 1 mm STE and proportionally excessive discordant STE, as defined by ≥ 25% of the depth of the preceding S-wave.
See the modified Sgarbossa criteria in action in this excellent case study by Stephen Smith.
- This patient presented with chest pain and had elevated cardiac enzymes.
- Baseline ECG showed typical LBBB.
- There is 1mm concordant ST elevation in aVL (= 5 points).
- Other features on this ECG that are abnormal in the context of LBBB (but not considered “positive” Sgarbossa criteria) are the pathological Q wave in lead I and the concordant ST depression in the inferior leads III and aVF.
- This constellation of abnormalities suggests to me that the patient was having a high lateral infarction.
Positive Sgarbossa criteria in a patient with a ventricular paced rhythm:
- There is concordant ST depression in V2-5 (= Sgarbossa positive).
- The morphology in V2-5 is reminiscent of posterior STEMI, with horizontal ST depression and prominent upright T waves.
This patient had a confirmed posterior infarction, requiring PCI to a completely occluded posterolateral branch of the RCA.
Amal Mattu presents a case of acute myocardial infarction in the presence of left bundle branch block.
Plea for more ECG examples
We are a little short on good examples of positive Sgarbossa criteria. If you have an case that you would like to contribute to LITFL, please email to email@example.com and we will upload to this page. Thanks!
- ECG Medical Training – Sgarbossa Criteria – Part 1
- ECG Medical Training – Sgarbossa Criteria – Part 2
- ECG Medical Training – Sgarbossa Criteria – Part 3
- Sgarbossa rule update from Sgarbossa et al – American Heart Journal 2013
- STEMI in the context of LBBB – by Stephen Smith at EP Monthly
- Excellent ECG cases exploring ischaemia in the context of LBBB – Dr Smith’s ECG Blog
- Left bundle branch block – LITFL
- Smith SW et al. Diagnosis of ST Elevation Myocardial Infarction in the Presence of Left Bundle Branch Block using the ST Elevation to S-Wave Ratio in a Modified Sgarbossa Rule. Annals of Emergency Medicine 2012;60:766-76. [PMID 22939607]
- Sgarbossa EB et al. Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. GUSTO-1. N Engl J Med 1996 Feb 22; 334(8) 481-7. doi:10.1056/NEJM199602223340801 pmid:8559200. PubMed HubMed [LBTB]
- Wong CK et al. Patients with prolonged ischemic chest pain and presumed-new left bundle branch block have heterogeneous outcomes depending on the presence of ST-segment changes. J Am Coll Cardiol 2005 Jul 5; 46(1) 29-38. doi:10.1016/j.jacc.2005.02.084 pmid:15992631. PubMed HubMed [Wong]
- Klimczak A et al. Electrocardiographic diagnosis of acute coronary syndromes in patients with left bundle branch block or paced rhythm. Cardiol J 2007; 14(2) 207-13. pmid:18651461. PubMed HubMed 
- Madias JE. The nonspecificity of ST-segment elevation > or =5.0 mm in V1-V3 in the diagnosis of acute myocardial infarction in the presence of ventricular paced rhythm. J Electrocardiol 2004 Apr; 37(2) 135-9. pmid:15127382. PubMed HubMed 
- Sgarbossa EB, Pinski SL, Gates KB, and Wagner GS. Early electrocardiographic diagnosis of acute myocardial infarction in the presence of ventricular paced rhythm. GUSTO-I investigators. Am J Cardiol 1996 Feb 15; 77(5) 423-4. pmid:8602576. PubMed HubMed [Gusto]
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