Sgarbossa Criteria For Left Bundle Branch Block (LBBB)

Sgarbossa criteria explained

When a left bundle-branch block or VPR (ventricular paced rhythm) is present on the electrocardiogram, findings of acute myocardial infarction may be concealed.

This model aims to increase accuracy of AMI diagnosis in the presence of LBBB as it is considered that approximately 1 in 200 patients with myocardial infarction also have a left block.

The original Sgarbossa criteria consists of the following:

The initial observations in the original study relied on the fact that the ST-segment deviation is measured at the J point. Concordance and discordance of ST segments are analysed by comparison to the main direction of the QRS complex.

In ventricular-paced electrocardiograms, the most clinically useful criterion (for AMI diagnosis) is usually the ST-segment elevation >5mm discordant with the QRS complex.

According to a study by Smith, the Sgarbossa criteria can be improved in sensitivity (from 52 to 91%) by changing the third criterion:

From:

ST elevation ≥5 mm in a lead with downward (discordant) QRS complex.

To:

ST depression OR elevation discordant w/ the QRS complex and w/ a magnitude of at least 25% of the QRS.

However, this change leads to a reduction in the specificity of the diagnosis rule by 8%.

Currently, the possibility of using ventricular paced ECG in the evaluation of heart conditions such as acute chest pain, is explored.

Interpretation

The original and modified criteria have different interpretation methods, the original Sgarbossa tool is a scoring system where a cut off is applied whilst the modified criteria by Smith states that if at least one criterion is present, AMI diagnosis is highly likely.

Please note that even if the criteria rules out myocardial infarction diagnosis, if clinical suspicions persist, EKG and cardiac biomarkers should be repeated.

About the study

The model is based on a 1996 study conducted by Sgarbossa et al. The base-line electrocardiograms of patients enrolled in the GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) trial, with enzyme diagnosed AMI in the presence of LBBB were compared with electrocardiograms of control patients who had chronic coronary artery disease and LBBB.

Of 26,003 patients, 131 (0.5 percent) with acute myocardial infarction had left bundle-branch block. The three electrocardiographic criteria with independent value in the diagnosis of AMI were used in a multivariate model to develop a scoring system (0 to 10).

The model was validated as a clinical prediction rule for the diagnosis of acute myocardial infarction in patients with chest pain and left bundle-branch block.

Left bundle branch block and AMI

AMI diagnosis is difficult to establish electrocardiographically in patients with LBBB or a ventricular paced rhythm because of the baseline ST segments and T waves that tend to shift in a discordant direction, thus hiding or mimicking evidence of AMI.

In these patients, several ECGs and enzyme testing are required to discover the ischemia signs.

The most common causes include aortic stenosis, hypertension, ischemic heart disease, anterior MI, fibrosis, cardiomyopathy or digoxin toxicity.

Here are five findings that are characteristic of left bundle branch block diagnosis:

■ QRS duration of >120 ms;

■ Dominant S wave in V1;

■ Broad monophasic R wave in lateral leads (I, aVL, V5-V6);

■ Absence of Q waves in lateral leads (I, V5-V6; small Q waves are still allowed in aVL);

■ Prolonged R wave peak time >60ms in left precordial leads (V5-6).

Original source

Sgarbossa EB, Pinski SL, Barbagelata A, Underwood DA, Gates KB, Topol EJ, Califf RM, Wagner GS. Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) Investigators. N Engl J Med. 1996; 334(8):481-7.

Validation

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.

Other references

1. Cai Q, Mehta N, Sgarbossa EB, Pinski SL, Wagner GS, Califf RM, Barbagelata A. 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; 166(3):409-13.

2. Larson DM, Menssen KM, Sharkey SW, Duval S, Schwartz RS, Harris J, Meland JT, Unger BT, Henry TD. "False-positive" cardiac catheterization laboratory activation among patients with suspected ST-segment elevation myocardial infarction. JAMA. 2007; 298(23):2754-60.

3. Jain S, Ting HT, Bell M, Bjerke CM, Lennon RJ, Gersh BJ, Rihal CS, Prasad A. Utility of left bundle branch block as a diagnostic criterion for acute myocardial infarction. Am J Cardiol. 2011; 107(8):1111-6.