Sgarbossa Criteria for Left Bundle Branch Block (LBBB) Calculator

How does this Sgarbossa criteria for left bundle branch block (LBBB) calculator work?

This health calculator determines the possibility of the patient suspected with Left Bundle Branch Block (LBBB) to be diagnosed with ST elevation acute myocardial infarction.

The model originates from the 1996 study by Sgarbossa, a retrospective review of 17 ventricular paced ECGs with the diagnosis of acute myocardial infarction confirmed by cardiac biomarkers. The initial observations relied on the fact that the ST-segment deviation is measured at the J point. Concordance and discordance of ST segments are analyzed by comparison to the main direction of the QRS complex.

In ventricular-paced ECGs, the most clinically useful Sgarbossa criterion in identifying AMI is usually the ST-segment elevation >5mm discordant with the QRS complex. Revealing this early, helps in identifying the patients with AMI and initiating treatment.

The Sgarbossa criteria for left bundle branch block calculator facilitates the diagnosis stage and proposes 2 tabs, each with the two versions of the model available, the original and the Smith modified version.

The first tab uses points to calculate and then interpret the diagnosis result while the second tab is based on the existence of at least one criterion in the patient ECG.

Sgarbossa criteria original and modified

The criteria is used in patients with prior left bundle branch block (it is considered that approximately 1 in 200 patients with myocardial infarction also have a left block) and comes as a help in the diagnosis of acute MI, a diagnosis that proves often difficult and time consuming in the setting of a VPR (ventricular paced rhythm).

The original three findings observed and then implemented by Sgarbossa are:

■ ST elevation ≥1 mm in a lead with upward (concordant) QRS complex - yes answers weighing 5 points (sensitivity 18%, specificity 94%);

■ ST depression ≥1 mm in lead V1, V2, or V3 - with positive answers weighing 3 points out of the total score (sensitivity 29%, specificity 82;

■ ST elevation ≥5 mm in a lead with downward (discordant) QRS complex - yes answers weighing 2 points out of the total (sensitivity 55%, specificity 88%).

The original Sgarbossa criteria sums the points obtained in the three rules and applies a cut off at 3 points as explained:

■ Scores below 3 are not indicative of a ST elevation myocardial infarction diagnosis being probable but don’t rule out myocardial infarction entirely. If clinical suspicions persists, EKG and enzyme determinations should be repeated.

■ Scores of 3 and above carry a 98% specificity in diagnosing ST elevation myocardial infarction.

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

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

This comes as a result of a study observing excessively discordant ST elevation. However, this change in the original rule reduces specificity with 8%. In Smith’s modified version, the evaluation/ cut off is considered when at least one of the three is positive.

Some studies now explore the possibility of using ventricular paced ECG in evaluating other heart conditions such as acute chest pain.

Left bundle branch block and AMI

In patients with LBBB or a ventricular paced rhythm, AMI diagnosis (interpreting the ECG) proves difficult because of the baseline ST segments and T waves that tend to shift in a discordant direction, thus resulting in hiding the evidence of acute myocardial infarction or in negative cases, mimicking AMI. In a normal diagnosis, it would require several ECG determinations to discover the ischemia signs.

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

Usually diagnosis criteria for left bundle branch block includes:

■ 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).

References

1) Smith SW, Dodd KW, Henry TD, Dvorak DM, Pearce LA. (2012) 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; 60(6):766-76.

2) Sgarbossa EB, Pinski SL, Barbagelata A, Underwood DA, Gates KB, Topol EJ, Califf RM, Wagner GS. (1996) 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; 334(8):481-7.

3) Tabas JA, Rodriguez RM, Seligman HK, Goldschlager NF. (2008) Electrocardiographic criteria for detecting acute myocardial infarction in patients with left bundle branch block: a meta-analysis. Ann Emerg Med; 52(4):329-336.

4) Costa D, Brady WJ, Edhouse J. (2002) ABC of clinical electrocardiography: Bradycardias and atrioventricular conduction block. BMJ; 324(7336): 535–538.