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Sgarbossa score

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Sgarbossa criteria ECG left bundle branch block

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Here is a comprehensive breakdown of the Sgarbossa Criteria — a scoring system for diagnosing acute MI in the presence of Left Bundle Branch Block (LBBB) or ventricular paced rhythm, where normal STEMI criteria don't apply.

Background

In LBBB, baseline ST-segment and T-wave changes are expected (discordant ST changes — opposite to the main QRS deflection). This makes diagnosing AMI on ECG challenging. Sgarbossa et al. derived three independent ECG predictors of AMI from the GUSTO-1 trial database (NEJM 1996).

Original Sgarbossa Criteria (Weighted Score)

CriterionDescriptionPoints
1. Concordant STEST elevation ≥ 1 mm in a lead where the QRS is positive (concordant)5
2. Concordant STDST depression ≥ 1 mm in leads V1–V3 (concordant — QRS mainly negative here in LBBB)3
3. Discordant STEST elevation ≥ 5 mm in a lead where the QRS is negative (discordant)2
Interpretation: A total score ≥ 3 achieves ~90% specificity for AMI.
  • Criterion 1 alone (score = 5) → highly specific
  • Criterion 2 alone (score = 3) → meets threshold
  • Criterion 3 alone (score = 2) → does NOT meet threshold; needs additional criteria or workup

Modified Sgarbossa Criteria (Smith, 2012)

The original criterion 3 (discordant STE ≥ 5 mm) has poor sensitivity. The modified criteria replace it with a ratio-based rule:
ST/S ratio: Discordant ST elevation amplitude ÷ S-wave depth
  • ST/S ratio ≤ −0.25 (i.e., STE is >25% of the S-wave depth) = diagnostic of AMI
  • This removes the arbitrary 5 mm cutoff and accounts for QRS amplitude variation
  • Increases sensitivity without significant loss of specificity

Visual Summary

Sgarbossa Criteria — original (A: 5/3/2 point criteria) and Modified Sgarbossa/Smith criterion (B: ST/S ratio)
Panel A: Original three Sgarbossa criteria (5, 3, 2 points). Panel B: Modified Sgarbossa — ST/S ratio of 3.2/−10.0 = −0.32 (exceeds 0.25 threshold → AMI). Panels C & D: Real 12-lead ECG examples.

Key Clinical Points

  • Applies to both LBBB and ventricular paced rhythm (pacemaker creates similar baseline ST distortion)
  • New or presumably new LBBB in a patient with chest pain is high-risk even if Sgarbossa criteria are not met — treat as potential AMI
  • A LBBB that does NOT meet Sgarbossa criteria is still a marker of significant cardiovascular risk
  • Serial ECGs, echocardiography, and troponins are important adjuncts when ECG is non-diagnostic
  • Sgarbossa criteria do not apply to RBBB (the repolarization pattern differs)

Practical Approach

  1. Is the ST change concordant? (same direction as main QRS deflection)
    • STE ≥ 1 mm concordant → strong evidence of AMI (5 pts)
    • STD ≥ 1 mm in V1–V3 concordant → moderate evidence (3 pts)
  2. Is there excessive discordant STE?
    • Classic: ≥ 5 mm → weak evidence (2 pts)
    • Modified: ST/S ratio ≤ −0.25 → positive (better rule)
  3. Score ≥ 3 or any single concordant finding → treat as STEMI equivalent, consider emergent cath
— ROSEN's Emergency Medicine: Concepts and Clinical Practice; The Washington Manual of Medical Therapeutics
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Interpretation

ECG Interpretation

Patient details visible: HR ~91 bpm, BP 140/80 (handwritten), BSL 140 mg/dL, 12-lead ECG

Rhythm & Rate

  • Rate: ~91 bpm (regular)
  • Rhythm: Sinus rhythm

Key Findings

1. LBBB (Left Bundle Branch Block) ✅

  • Wide QRS complexes (visually >120 ms)
  • Broad monophasic R waves in I, aVL, V5, V6
  • Deep S waves / rS pattern in V1–V3
  • Discordant ST-T changes (expected in LBBB)

2. Machine Interpretation confirms:

  • "Atrial Enlargement"
  • "Atrial Infarction (Recent)"
  • "Abnormality (Negative T)" — likely referring to T-wave inversions

Applying Sgarbossa Criteria (given LBBB)

CriterionFinding on this ECG
Concordant STE ≥ 1 mmPossible in lateral leads (V5–V6, I) — look for STE in same direction as QRS
Concordant STD ≥ 1 mm in V1–V3V1–V3 show deep S waves; ST changes need careful measurement
Discordant STE ≥ 5 mmPresent in V1–V3 (expected in LBBB — need to assess if excessive)
From the ECG image, there appear to be:
  • Deeper-than-expected discordant ST changes in V1–V3 — assess ST/S ratio (Modified Sgarbossa)
  • Lateral lead ST morphology — the ST segments in V5–V6 should be scrutinized for concordant elevation

Machine Diagnosis: "Atrial Infarction (Recent)"

This is an uncommon but recognized pattern — atrial MI can cause:
  • PR segment elevation in aVR with PR depression in lateral leads
  • Abnormal P wave morphology
  • The machine flag warrants clinical correlation

Summary Interpretation

Sinus rhythm at ~91 bpm with LBBB (likely pre-existing or new — clinically critical to determine). Machine flags recent infarction. Sgarbossa criteria should be formally applied with caliper measurement.

⚠️ Clinical Bottom Line

Given the LBBB + machine flag of "recent infarction" + BSL 140 + BP 140/80:
  • New LBBB in a chest pain patient = STEMI equivalent until proven otherwise
  • Apply Modified Sgarbossa (ST/S ratio ≤ −0.25 in any lead = positive)
  • Serial ECGs, troponins, and urgent cardiology review are mandatory
  • Compare with any prior ECG to determine if LBBB is new
This ECG requires urgent clinical correlation — do not rely solely on machine interpretation.

Why this is not AIVR?

Great clinical question. Here's why this ECG is not AIVR:

AIVR vs LBBB — Key Differentiators

What is AIVR?

Accelerated Idioventricular Rhythm = ventricular escape rhythm that "accelerates" to 40–120 bpm, producing wide QRS complexes.

Why This ECG is NOT AIVR

1. P waves are present and conducting ✅

  • In this ECG, P waves precede every QRS with a consistent PR interval
  • AIVR is an AV-dissociated rhythm — P waves are either absent, dissociated, or retrograde
  • Here, sinus node is in control → rules out AIVR by definition

2. Rate is 91 bpm

RhythmTypical Rate
Idioventricular (escape)20–40 bpm
AIVR40–120 bpm
Ventricular tachycardia>120 bpm
  • Rate of 91 bpm is within AIVR range numerically, but — the presence of conducted P waves excludes it

3. QRS morphology is LBBB-pattern, not typical ventricular origin

  • AIVR typically originates from the right ventricle → produces an LBBB-like pattern (which can cause confusion)
  • However, LBBB from a supraventricular origin has:
    • Consistent QRS morphology beat to beat ✅
    • Fixed PR interval ✅
    • No fusion beats (fusion beats = hallmark of AIVR/VT)
  • AIVR characteristically shows fusion beats at onset and termination as the ventricular focus competes with the sinus node

4. No AV Dissociation

  • AIVR requires AV dissociation (ventricles fire independently of atria)
  • This ECG shows 1:1 P:QRS relationship → purely supraventricular conduction with aberrancy (LBBB)

5. Clinical Context

  • AIVR is classically seen in:
    • Reperfusion (post-thrombolysis / post-PCI) — "reperfusion arrhythmia"
    • Acute inferior MI
    • Digoxin toxicity
    • Cocaine use
  • This patient has hypertension + elevated BSL — more consistent with a chronic LBBB substrate

Summary Table

FeatureThis ECGAIVR
P wavesPresent, conductingAbsent / dissociated
PR intervalFixed, normalNone or variable
AV relationship1:1Dissociated
Fusion beatsNoneTypically present
QRS originSupraventricular + BBBVentricular (ectopic focus)
Rate91 bpm (sinus-driven)40–120 bpm (ventricular-driven)
Bottom line: The wide QRS in this ECG is due to aberrant conduction (LBBB) from a sinus-driven impulse — not a ventricular ectopic focus. The presence of conducted P waves with a fixed PR interval is the single most important distinguishing feature.
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