Sgarbossa Criteria and Modified Sgarbossa Calculator for LBBB and Paced Rhythms

Criteria

1. Concordant ST elevation of 1 mm or more

   In any lead where the QRS is mostly positive. Original score: 5 points, enough on its own.

2. Concordant ST depression of 1 mm or more in V1, V2 or V3

   In the right precordial leads, where the QRS of LBBB is mostly negative. Original score: 3 points, also enough on its own.

3. Excessively discordant ST elevation, original rule

   ST elevation of 5 mm or more in a lead where the QRS is mostly negative. Original score: 2 points, so it can't reach the cutoff of 3 alone.

4. Proportionally excessive discordant ST elevation, Smith's rule

   ST elevation of at least 1 mm that is 25% or more of the depth of the preceding S wave, an ST/S ratio of -0.25 or less. It replaces the 5 mm rule.

5. Scoring

   Original: add the points; 3 or more is positive. Modified: unweighted, positive with any one rule.

How to measure it

1. Confirm the pattern: left bundle branch block (QRS of 120 ms or more, broad notched R in I, aVL, V5 and V6, deep S in V1) or a ventricular paced rhythm.
2. In each lead, measure the ST deviation at the J point against the PR segment, in mm.
3. Note whether the QRS in that lead is mostly positive or mostly negative. ST moving the same way as the QRS is concordant; the opposite way is discordant.
4. For each lead with discordant ST elevation of 1 mm or more, measure the depth of the S wave from the baseline.
5. Divide the ST elevation by the S depth. A result of 0.25 or more, written as an ST/S ratio of -0.25 or less, meets Smith's third rule.

What to do

• Treat a positive modified Sgarbossa result in a patient with ischemic symptoms as a STEMI equivalent and call the cath lab team, as local protocol directs.
• Don't treat new or presumed new LBBB alone as a STEMI equivalent. Decide on the ST changes, the symptoms, the hemodynamics and the troponin.
• If the ECG is negative but suspicion stays high, repeat it at short intervals, compare with an old ECG and get an urgent echocardiogram to look for a new wall motion abnormality.
• Patients with LBBB in shock, or with ongoing ischemic pain despite treatment, need urgent angiography whatever the ECG shows.

Key studies

• Sgarbossa 1996, N Engl J Med

  Of 26,003 North American patients in the GUSTO-1 trial, 131 had acute MI with LBBB. Three ST criteria predicted infarction independently and were combined into a 0 to 10 score that made a highly specific diagnosis possible.

  Paper

• Smith 2012, Ann Emerg Med

  In 33 patients with LBBB and an angiographically occluded artery and 129 controls, replacing the 5 mm rule with an ST/S ratio of -0.25 or less raised sensitivity to 91%, from 52% for the weighted score, with 90% specificity.

  Our summaryPaper

• Meyers 2015, Am Heart J

  In a separate cohort of 45 occlusions and 249 controls, the modified criteria were 80% sensitive and 99% specific, against 49% and 100% for the original weighted criteria.

  Paper

• Dodd 2021, Ann Emerg Med (PERFECT)

  In ventricular paced rhythm, the modified criteria found 81% of occlusion MIs against 56% for the original criteria, with 96% specificity in emergency department controls.

  Paper