Sgarbossa's Criteria for MI in Left Bundle Branch Block

Diagnosing acute myocardial infarction (MI) in the presence of left bundle branch block (LBBB) is challenging because baseline ventricular depolarization and repolarization abnormalities can obscure typical ischemic ST-segment patterns. Sgarbossa's criteria provide a structured ECG-based method to identify findings that are more specific for acute coronary occlusion in this setting.

This calculator applies the original weighted Sgarbossa criteria and returns a total score to help clinicians rapidly stratify suspicion for MI in patients with LBBB (or paced rhythms, when used with caution and clinical context). It is an adjunct to urgent bedside assessment, serial ECG review, biomarker trends, and institutional reperfusion pathways.

When this calculator is useful

• Chest pain or ischemic symptoms with known or presumed LBBB on ECG.
• Hemodynamic instability where rapid ECG triage is needed.
• Emergency and critical care settings requiring high-specificity ECG signals for occlusion MI concern.
• Clinical scenarios where immediate interpretation must be integrated with troponins and imaging.

Original Sgarbossa criteria (weighted)

Three ECG findings are scored:

1. Concordant ST elevation ≥ 1 mm in any lead — 5 points
2. Concordant ST depression ≥ 1 mm in V1–V3 — 3 points
3. Excessively discordant ST elevation ≥ 5 mm — 2 points

The first two findings (concordant changes) are uncommon in uncomplicated LBBB and therefore carry stronger diagnostic weight. The third criterion uses an absolute cutoff and is less specific when QRS amplitude is very large.

How scoring is interpreted

The classic threshold is total score ≥ 3, which is generally considered highly specific for acute MI in the appropriate clinical context. A score below 3 does not safely exclude MI because sensitivity of the original criteria is limited.

• Score ≥ 3: Strongly supports high-risk ACS/occlusion concern; expedite emergent evaluation and local reperfusion workflow as indicated.
• Score < 3: Does not rule out MI; continue serial ECGs, serial troponins, reassessment, and adjunct imaging.

Bedside workflow with this calculator

1. Confirm LBBB morphology and ensure ECG quality is adequate.
2. Evaluate each Sgarbossa criterion carefully, lead by lead.
3. Enter present findings into the calculator to obtain the weighted score.
4. Integrate result with symptoms, timing, hemodynamics, and risk profile.
5. Repeat ECG and biomarkers if diagnosis remains uncertain.
6. Escalate rapidly when clinical picture suggests ongoing ischemia despite indeterminate score.

Clinical nuance and practical interpretation

A positive Sgarbossa score should be interpreted as a high-value ECG signal rather than an isolated diagnosis. The pretest probability of ACS matters substantially. For example, ongoing chest pain, diaphoresis, hypotension, dynamic ECG changes, or wall-motion abnormality on bedside echo materially increase concern for occlusive MI and may justify urgent cath lab activation depending on protocol.

Conversely, patients with chronic structural heart disease, baseline LBBB, or non-ischemic causes of troponin elevation can present with complex ECG patterns. In these cases, trend-based reassessment and multimodal data are essential.

Modified Sgarbossa context

Many clinicians also consider the modified Sgarbossa approach, which replaces the absolute 5 mm discordant elevation criterion with a proportional rule (ST/S ratio threshold). This may improve sensitivity in some cohorts, especially when QRS voltages vary widely. Even so, any ECG rule should be interpreted as part of an integrated ACS strategy rather than a standalone decision tool.

Common pitfalls

• Using score < 3 as a rule-out test for MI.
• Ignoring dynamic changes across serial ECGs.
• Overcalling discordant elevation without considering QRS amplitude and lead context.
• Failing to reconcile ECG findings with symptoms, troponin trajectory, and bedside imaging.
• Delays in escalation when high-risk clinical features are present despite uncertain score.

What this calculator provides

• Rapid computation of original weighted Sgarbossa score (5/3/2).
• Threshold-based flag for classic positivity (≥3 points).
• Structured interpretation text for bedside documentation.
• Educational support for clinicians and trainees learning LBBB ischemia assessment.

Intended use and scope

This calculator is designed for professional clinical education and decision support. It assists interpretation of ECG findings in suspected ACS with LBBB, but it does not replace physician judgment, local pathways, or urgent specialist care in potentially time-sensitive myocardial ischemia.