It is often difficult to identify a ST-Elevation Myocardial Infarction (STEMI) in a patient with an Electrocardiogram (EKG) showing an existing left bundle branch block (LBBB). That’s because, EKGs with LBBBs normally have discordant ST segments and T waves (the deflection of the QRS and ST/T-wave segment go in the opposite direction). This is called “appropriate discordance” because it expected on EKGs with LBBBs. However this discordance can mask signs of acute myocardial infarctions. The Sgarbossa Criteria, is a tool that you can use to help read through EKGs with LBBBs in patients you are concerned for myocardial ischemia. It’s composed of 3 criteria on a scale from 0-5.
Concordant ST elevation < 1mm in leads with a positive QRS complex (Score 5)
In this case, the QRS complex and ST segment both have a positive deflection. This is called concordance. If the concordant ST elevation is greater than 1 mm, you would assign 5 points.
Concordant ST depression > 1mm in V1-V3 (Score 3)
Here, you have both the QRS complex and the ST segment in a negative deflection. Because they are going in the same direction, you still call this concordance. If the concordant ST depression is greater than 1 mm, you would assign 3 points.
Excessively discordant ST elevation > 5mm in leads with a negative QRS complex (Score 2)
In this criteria, you are focusing on QRS complexes with negative deflections. In these EKG waves, you are looking for ST segments which have positive deflections - you would call this discordance because the QRS complex and ST segments go in opposite directions. When the discordance is greater than 5mm, in leads with a negative QRS complex, you would assign 2 points.
Here we have concordant ST-elevation in leads II, V5, and V6 and concordant ST-depression in lead V1, V2, and V3. This patient has a Sgarbossa Criteria of 8.
- Concordant ST elevation > 1 mm in leads with a positive QRS complex (score 5)
- Concordant ST depression > 1 mm in V1-V3 (score 3)