Healthcare & Clinical Calculations
Smith-Modified Sgarbossa Criteria for LBBB & Paced Occlusion MI (STEMI)
Evaluate acute coronary occlusion in left bundle branch block (LBBB) or right-ventricular paced rhythms using concordant ST shifts (>= 1 mm) and Stephen Smith’s proportional discordant ST/S ratio (<= -0.25).
Replace the blunt >= 5 mm Sgarbossa cutoff with Smith’s proportional ST/S <= -0.25 rule!
Left Bundle Branch Block (LBBB) and right-ventricular (RV) paced rhythms normally produce discordant ST elevation in leads with deep negative S-waves—masking or mimicking acute STEMI! Elena Sgarbossa’s original 1996 third criterion required an arbitrary fixed >= 5 mm of discordant ST elevation: that missed subtle LAD occlusions in low-voltage leads (52% sensitivity) while triggering false cath-lab activations in severe left ventricular hypertrophy (LVH) with giant -25 to -30 mm S-waves!
Stephen W. Smith et al. (Annals of Emergency Medicine 2012; BARCELONA / Pendell Meyers validation) replaced the fixed 5 mm rule with the proportional ST-Elevation-to-S-Wave Amplitude Ratio (ST/S <= -0.25 in any single lead with >= 1 mm STE and a negative S-wave), jumping sensitivity from 52% to 91% at 90% specificity! Look at the contrast: a lead with +5.5 mm discordant STE following an -18.0 mm S-wave yields ST/S = -0.306 (<= -0.25 -> Positive Occlusion MI!), whereas a giant LVH lead with +5.0 mm STE following a -25.0 mm S-wave yields ST/S = -0.200 (> -0.25 -> Negative, avoiding a false-positive angiogram)!
| 12-Lead LBBB / RV-Paced ECG Pattern | Concordant Shift or ST/S Ratio | Smith-Modified Sgarbossa Result | Emergency Cath-Lab Action |
|---|---|---|---|
| Concordant STE >= 1 mm (Any Lead) or Concordant STD >= 1 mm (V1-V3) | Direct Concordant Injury | Positive (100% Specific Rule) | Immediate Emergent Reperfusion |
| Discordant +5.5 mm STE on -18.0 mm S-Wave | ST / S = -0.306 (<= -0.25) | Positive Proportional Discordance | Activate Cath Lab (OMI Detected) |
| Giant LVH +5.0 mm STE on -25.0 mm S-Wave | ST / S = -0.200 (> -0.25) | Negative (Appropriate Discordance) | Avoid False-Positive 1996 Trigger |
Proportional Discordant ST-Elevation / S-Wave Ratio (ST / S)
Computes ST_elev / S_wave (negative ratio when B4 >= 1 mm STE opposes negative S-wave amplitude B5 < 0 mm).
=IF(OR(B2 < 0, B3 < 0, B4 < 0), "Invalid ECG Amplitude", IF(AND(B4 >= 1, B5 < 0), ROUND(B4 / B5, 3), 0))Smith-Modified Sgarbossa Acute Coronary Occlusion (OMI) Decision
Triggers positive when concordant STE >= 1 mm (B2), concordant V1-V3 STD >= 1 mm (B3), or discordant ST/S <= -0.25 with STE >= 1 mm.
=IF(OR(B2 < 0, B3 < 0, B4 < 0), "Invalid ECG Amplitude", IF(OR(B2 >= 1, B3 >= 1, AND(B4 >= 1, B5 < 0, (B4 / B5) <= -0.25)), "Positive Smith-Sgarbossa — Acute Coronary Occlusion (STEMI Equivalent)", "Negative Smith-Sgarbossa — Appropriate LBBB/Paced Discordance"))Try the example
Use the original values or change them to test your understanding.