ECG criteria
- Concordant ST elevation ≥ 1 mm in any lead with a positive (concordant) QRS complex — 5 points
- Concordant ST depression ≥ 1 mm in V1, V2, or V3 (where QRS is usually negative) — 3 points
- Discordant ST elevation ≥ 5 mm in a lead with a negative (discordant) QRS — 2 points
- A total score of ≥ 3 points is highly specific for acute myocardial infarction / acute ischemic event; in the appropriate clinical context, it requires urgent evaluation for acute coronary occlusion
- Modified Smith criteria: for the third criterion, discordant ST elevation is evaluated as ≥ 1 mm in a lead with a negative QRS and the ratio of ST to the absolute depth of the S wave in the same lead ≥ 0.25 (with signed ST/S calculation ≤ −0.25); this is equivalent to ST elevation of at least 25% of the S-wave depth; the criterion is not calculated if the S wave is absent or practically unmeasurable; the modification applies only to the third criterion and does not change the point totals of the first two
- Any of the first two criteria (concordant elevation or depression) on its own already reaches the threshold of ≥ 3 points and requires immediate clinical evaluation and consideration for emergency coronary angiography; the final diagnosis of myocardial infarction is established based on the combination of clinical presentation, ECG, troponin, and imaging
What it looks like on ECG
In LBBB, the QRS complex is wide (≥ 120 ms), and the ST segment is physiologically discordant with the QRS: where the QRS points upward, the ST segment is usually displaced downward, and vice versa. This masks the usual signs of STEMI, which is why Sgarbossa proposed looking specifically for violations of this pattern.
| Criterion | Leads | Cut-off | Score |
|---|---|---|---|
| Concordant ST elevation | any, QRS upward | ≥ 1 mm | 5 |
| Concordant ST depression | V1–V3, QRS downward | ≥ 1 mm | 3 |
| Discordant ST elevation | QRS downward | ≥ 5 mm (orig.) or ≥ 1 mm when ST/S ≥ 0.25 (Smith) | 2 |
Concordancy means that ST and the main QRS wave are directed in the same direction — this is abnormal in LBBB and indicates superimposed acute ischemic injury. Discordancy is normally always present, which is why the threshold for it is much higher (5 mm) or the relative Smith criterion is used: discordant ST elevation ≥ 1 mm and its ratio to the S-wave depth in the same lead ≥ 0.25 (25%); this approach is more sensitive with small S-wave amplitudes, when the absolute 5 mm threshold is unattainable even with obvious ischemia.
ST displacement is measured strictly at the J point, comparing the direction of displacement with the direction of the main QRS wave in the same lead — this is how both the original criteria and the Smith modification are defined. The general practice of measuring ST 60–80 ms after the J point (used when the J point is indistinct for standard STEMI criteria) is not validated as a replacement for the Sgarbossa criteria and can significantly alter the result in a wide QRS; for diagnosis using Sgarbossa/Smith, measurement is performed at the J point, applying the same methodology when comparing serial ECGs.
Mechanism
In LBBB, ventricular depolarization occurs abnormally via the right bundle branch with a delay to the left ventricle, which is why repolarization (ST segment, T wave) is characteristically discordant with QRS — this is so-called secondary (non-ischemic) discordancy. Acute ischemia or coronary artery occlusion creates pathological injury currents that alter the ST vector independently of the block and disrupt the expected secondary discordancy. This can manifest either as concordant ST displacement (where it normally should not be) or sharply enhanced discordant elevation where it was already expected.
Causes
- Acute coronary artery occlusion (most commonly the left anterior descending, but any localization is possible) against the background of baseline LBBB
- The same situation during ventricular pacing (paced wide QRS mimics LBBB)
- Chronic LBBB without ischemia: criteria can be positive even without acute ischemia (especially the absolute criterion of discordant ST elevation ≥ 5 mm), yielding a false-positive result; comparison with a prior ECG, clinical presentation, serial ECGs, and troponin dynamics help assess whether there is acute evolution
Differential diagnosis
- Simple LBBB without ischemia: ST discordancy is present, but does not reach threshold values, no concordancy
- Left ventricular hypertrophy with LBBB: can produce marked ST discordancy, but without a concordant component and usually without evolution on serial ECGs
- Ventricular pacing pattern without ischemia: Sgarbossa/Smith criteria apply similarly, but thresholds are initially less studied than for LBBB
- Prior myocardial infarction with scar ST-T changes: no acute evolution, no clinical correlation
Clinical significance and management
Positive Sgarbossa criteria (score ≥ 3 points), especially the isolated concordant sign, in a patient with ongoing ischemic symptoms and known or newly discovered LBBB (or paced rhythm) should be regarded as highly suspicious for acute coronary occlusion. In the presence of ongoing ischemic symptoms, positive highly specific criteria require immediate activation of the interventional team and consideration for emergency coronary angiography; troponin and imaging data are evaluated in parallel and should not delay emergency reperfusion. New or presumed new LBBB by itself is no longer considered an independent STEMI equivalent. The modified Smith criteria increase the test's sensitivity and are preferred where assessment of the ST/S ratio is available. Negative criteria do not rule out ACS: clinical evaluation, troponin dynamics, and serial ECGs are needed; if clinical probability is high, consultation with an interventional cardiologist is warranted regardless of the formal score.
Common interpretation errors
- Applying standard STEMI criteria (age/sex thresholds in V2–V3 without accounting for LBBB) instead of Sgarbossa
- Confusing discordancy (normal in LBBB) with a pathological sign — forgetting to compare the amplitude against the threshold
- Failing to calculate the ST/S ratio according to Smith criteria where the S wave is small, thereby missing significant elevation, or attempting to apply it when the S wave is unmeasurable
- Interpreting positive criteria in chronic LBBB as definitive proof of acute ischemia without comparing to a prior ECG
- Applying criteria in a normal narrow QRS without LBBB or paced rhythm, where they are not validated
Concordancy rules: ST 'in the same direction as QRS' is a red flag; even a single such lead outweighs the point total.
1. How many points in the original Sgarbossa criteria correspond to concordant ST elevation ≥ 1 mm in a lead with a positive QRS?
Concordant ST elevation ≥ 1 mm is the most specific sign and is assigned the maximum value of 5 points.
2. What is the essence of the Smith modification compared to the original third Sgarbossa criterion?
Smith proposed evaluating discordant ST elevation (≥ 1 mm) relative to the absolute depth of the S wave (ST/S ≥ 0.25), which increases sensitivity when the S-wave amplitude is small.
3. In a patient with chronic LBBB and chest pain, the Sgarbossa criteria are positive. What is the correct management strategy?
Positive highly specific criteria in the presence of ongoing ischemia require immediate activation of the invasive team; troponin and imaging are evaluated in parallel and should not delay reperfusion.
Frequently asked questions
Can Sgarbossa criteria be applied in typical intraventricular conduction delay without LBBB?
No, the criteria were developed and validated specifically for LBBB and ventricular pacing. In other variants of wide QRS (e.g., RBBB), they are not applicable and have not been studied to the same extent.
How do Smith's modified criteria differ from the original Sgarbossa criteria?
The original third criterion requires discordant ST elevation ≥ 5 mm in absolute units, which reduces sensitivity when the S-wave amplitude is small. Smith replaced it with a combination: discordant ST elevation ≥ 1 mm and the ratio of this elevation to the absolute depth of S in the same lead ≥ 0.25. This increases sensitivity; in validated studies, the criterion maintains high, although sometimes slightly lower, specificity compared to the original absolute threshold.
Is a single positive criterion sufficient to diagnose infarction?
An isolated concordant ST elevation or depression (the first or second criterion) on its own already reaches the threshold of ≥ 3 points and is considered a highly specific sign of an acute ischemic event. This requires immediate evaluation and usually emergency coronarography when corresponding clinical symptoms are present, though it is not a standalone definitive confirmation of infarction — the diagnosis is established based on the combination of clinical presentation, ECG, troponin, and imaging.
Are Sgarbossa criteria applicable in a patient with a pacemaker?
Yes, the same logic of ST concordance/discordance relative to QRS is used in ventricular pacing, although this population has been studied less than patients with LBBB.
What should be done if the criteria are negative, but the clinical presentation is suspicious for ACS?
A negative result does not rule out acute coronary occlusion. Serial ECGs, troponin dynamics, and clinical evaluation are required; if suspicion persists, the decision for emergency angiography is made taking the full clinical picture into account, not just the Sgarbossa score.
ECG Course
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Related terms
More in the section "Ischemia and Myocardial Infarction"
Sources
- Sgarbossa E.B. et al., New England Journal of Medicine, 1996 (original criteria)
- Smith S.W. et al. — modified criteria (ST/S ratio)
- Surawicz B., Knilans T. — Chou's Electrocardiography in Clinical Practice
- ESC Guidelines — ACS, current edition
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.