ECG criteria
- QTc according to Bazett's formula ≥ 480 ms — 3.5 points (in the older version of the scale — 3 points)
- QTc 460–479 ms — 2 points
- QTc 450–459 ms (in males) — 1 point
- QTc ≥ 480 ms at the 4th minute of recovery after an exercise test — 1 point
- Torsades de pointes — 2 points
- T-wave alternans — 1 point
- Notched T wave in three leads — 1 point
- Resting heart rate below the 2nd percentile for age — 0.5 points
What it looks like on ECG
The Schwartz score is not a single ECG pattern, but the total sum of points from three groups of criteria: ECG, clinical presentation, and family history. The ECG evaluation assesses the heart rate-corrected QT interval (QTc), measured from the beginning of the QRS complex to the end of the T wave in the lead where the T-wave end is most reliably determined, usually II or V5; if discrepancies exist between leads, the longest correctly measured QT is used.
| Sign | Score |
|---|---|
| QTc ≥ 480 ms | 3.5 (older version of the scale — 3) |
| QTc 460–479 ms | 2 |
| QTc 450–459 ms (males) | 1 |
| QTc ≥ 480 ms at the 4th min of recovery after exercise | 1 |
| Torsades de pointes | 2 |
| T-wave alternans | 1 |
| Notched T wave in ≥ 3 leads | 1 |
| Resting heart rate below the 2nd percentile for age | 0,5 |
| Syncope with stress | 2 |
| Syncope without stress | 1 |
| Congenital deafness | 0,5 |
| Confirmed LQTS in a family member | 1 |
| Unexplained sudden cardiac death in a first-degree relative under 30 years of age | 0,5 |
Clinical criteria are added to the ECG points (syncope with stress — 2 points, syncope without stress — 1 point; congenital deafness — 0.5 points) and family criteria (confirmed LQTS in a family member — 1 point; unexplained sudden cardiac death in a first-degree relative under 30 years of age — 0.5 points). Within the ECG category, independent features — QTc, torsades de pointes, T alternans, notched T, and low heart rate — are added together if present simultaneously. Only mutually exclusive grades of the same feature are not summed: for QTc, the single highest applicable grade is taken; of the two syncope options, only one is chosen (the one with the higher score if both formally apply); of the family criteria, only one is also chosen. Then the points from the ECG, clinical, and family criteria are summed into the total score.
Mechanism
Long QT syndrome is associated with impaired function of cardiomyocyte ion channels — most commonly potassium (KCNQ1, KCNH2) or sodium (SCN5A) channels. Delayed repolarization increases the duration of the action potential, which manifests on the ECG as a prolongation of the QT interval. Repolarization prolongation promotes early afterdepolarizations and triggers activity; repolarization heterogeneity between myocardial layers maintains electrical instability, which clinically manifests as torsades de pointes. The Schwartz score combines probabilistic markers of this condition into a single scale to reduce diagnostic subjectivity in borderline QTc values.
Causes
- Congenital long QT syndrome (Romano–Ward syndrome, Jervell and Lange-Nielsen syndrome)
- Genetic channelopathies (KCNQ1, KCNH2, SCN5A, and others)
- Family predisposition to syncope and sudden cardiac death
- Acquired QT prolongation (medications, electrolyte disturbances) — not evaluated by this scale, but must be ruled out before its application
Differential diagnosis
- Acquired QT prolongation due to medications or electrolyte disturbances — requires correction of the reversible cause before diagnosing congenital LQTS; the Schwartz score is applied after ruling out secondary causes
- Borderline QTc prolongation in healthy individuals (for example, the upper limit of normal is higher in some women) — isolated moderate prolongation without clinical symptoms or family history yields a low score
- Short QT syndrome — directionally opposite interval change, a different scale, and a different clinical picture
- Incorrect QT measurement (fusion with U wave, low T-wave amplitude) — overestimates or underestimates the score
Clinical significance and management
The final score divides patients into probability groups: low (≤ 1 point), intermediate (1.5–3 points), and high (≥ 3.5 points) probability of congenital long QT syndrome. In intermediate probability, a correct repeat QTc measurement, exclusion of secondary causes of QT prolongation, thorough clinical evaluation, and consultation with a specialist in inherited arrhythmic syndromes are needed first; molecular genetic testing in this group is considered individually after phenotype confirmation. In high probability and clinically established LQTS diagnosis, genetic counseling and testing are recommended, along with screening of first-degree relatives, assessment of arrhythmic event risk, and decisions regarding pharmacotherapy or device implantation according to current guidelines. The scale does not replace genetic testing — some carriers of pathogenic variants have a normal or minimally altered QTc (incomplete penetrance).
Common interpretation errors
- Using uncorrected QT for heart rate instead of QTc
- Applying the scale without excluding medications and electrolyte disturbances that prolong QT
- Summing multiple grades of the same feature (e.g., two QTc ranges) instead of choosing the single highest one
- Measuring QT in a lead with an unclear T-wave end without checking adjacent leads
- Summing both syncope options or both family criteria instead of choosing one
- Ignoring a family history of sudden death at a young age when calculating points
1. How many points according to the current version of the Schwartz score correspond to resting QTc ≥ 480 ms?
QTc ≥ 480 ms is the maximum ECG criterion of the current scale, 3.5 points (in the old version — 3 points).
2. How many points does a confirmed LQTS in a family member add?
Confirmed LQTS in a relative is 1 point; this is a family criterion that is not summed with an unexplained sudden death of a relative.
3. What needs to be done before applying the Schwartz score in a patient with a prolonged QT?
The scale evaluates congenital LQTS, so secondary reversible causes of QT prolongation must be excluded in advance.
Frequently asked questions
What does the Schwartz score indicate?
The Schwartz score is a probability scale for congenital long QT syndrome, combining ECG data (primarily QTc), clinical syncope, and family history into a single point total.
What score is considered diagnostic?
A score of ≥ 3.5 points corresponds to a high probability of long QT syndrome, 1.5–3 points to an intermediate probability, and ≤ 1 point to a low probability.
Can the Schwartz score be used when taking QT-prolonging drugs?
The scale was developed for congenital LQTS, so acquired causes of QT prolongation—such as medications and electrolyte disturbances—must be excluded or corrected before using it.
Does the Schwartz score replace genetic testing?
No. In cases of high probability and a clinical diagnosis of LQTS, genetic testing is recommended; in intermediate probability cases, it is considered individually after phenotype confirmation, since some carriers of pathogenic variants have a normal QTc.
How are syncope and family history accounted for in the scoring?
Out of the syncope options (stress-induced — 2 points, non-stress-induced — 1 point), only one higher value is chosen. Out of the familial criteria (confirmed LQTS in a relative — 1 point, unexplained sudden death in a first-degree relative younger than 30 years — 0.5 points), only one is taken as well.
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Related terms
More in the section "Criteria, Formulas, Algorithms"
Sources
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice
- Goldberger A. Clinical Electrocardiography: A Simplified Approach
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.