Estimates pre-genetic test probability of congenital LQTS. Score ≥ 3.5 = High probability (>90%). Use Bazett QTc from resting 12-lead ECG (lead II or V5, average 3 beats).
QTc Interval (Bazett)
ECG Findings
Clinical History (Choose One Syncope)
Family History
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
Pre-genetic test probability estimation for congenital Long QT Syndrome (LQTS) in symptomatic or asymptomatic individuals with prolonged QTc.
Supporting clinical diagnosis of LQTS in individuals with QTc borderline (440–499ms) where cause is uncertain.
Triaging which patients warrant genetic testing for KCNQ1 (LQT1), HERG/KCNH2 (LQT2), and SCN5A (LQT3).
Endorsed in HRS/EHRA/APHRS 2013 Expert Consensus and ACC/AHA/HRS 2017 arrhythmia guidelines.
Section 2
Formula & Logic
Scoring Criteria
Criterion
Points
ECG FINDINGS
QTc ≥ 480ms (Bazett)
3
QTc 460–479ms
2
QTc 450–459ms (males)
1
QTc > 480ms during 4th minute of recovery from exercise stress test
1
Torsades de Pointes
2
T-wave alternans
1
Notched T-wave in 3 leads
1
Low heart rate for age (< 2nd percentile)
0.5
CLINICAL HISTORY
Syncope — with stress
2
Syncope — without stress
1
Congenital deafness (Jervell & Lange-Nielsen)
0.5
FAMILY HISTORY
Family members with definite LQTS
1
Unexplained sudden cardiac death < 30yrs in first-degree relative
0.5
Probability Classification
Total Score
LQTS Probability
≤ 1
Low (< 10%)
1.5–3
Intermediate (~30%)
≥ 3.5
High (> 90%)
Section 3
Pearls/Pitfalls
Key Pearls
QTc ≥ 480ms alone (Score 3) = High probability — genetic testing should proceed without waiting for further clinical events.
Stress-induced syncope + prolonged QTc together are a very high-risk combination — exclude LQT1/2 (swimming/exertion triggers).
Congenital deafness raises suspicion for Jervell & Lange-Nielsen Syndrome (homozygous KCNQ1) — autosomal recessive, more severe.
QTc should always be measured using Bazett formula from resting 12-lead ECG; measure 3 beats and average; use lead II or V5.
QTc Upper Limits (Normal)
Population
QTc Upper Limit
Men
< 440ms
Women
< 450ms
Children (< 15yr)
< 460ms
LQTS diagnostic threshold (both sexes)
≥ 480ms (high probability)
Section 4
Next Steps
Clinical Actions
01
Score ≤ 1: Reassure; exclude secondary QT prolongation (drugs, electrolytes, drugs); repeat ECG on another day.
02
Score 1.5–3: Cardiology and/or genetics referral; genetic testing if QTc ≥ 460ms; avoidance of QT-prolonging drugs; electrolyte optimisation.
03
Score ≥ 3.5: Confirmed clinical LQTS — initiate beta-blocker (nadolol/propranolol preferred); genetic testing to type; sport restriction counselling; ICD if prior aborted cardiac arrest.
04
All LQTS: Screen 1st degree relatives; advise avoidance of CredibleMeds QT-prolonging medications; genetic counselling.
Section 5
Evidence Appraisal
Primary Reference
Diagnostic criteria for the long QT syndrome. An update
Schwartz PJ et al. • Circulation. 1993;88(2): 782–784
Section 6
Literature
Development
Developed by Peter Schwartz and colleagues at the University of Pavia, Italy, first published in Circulation in 1985 and updated in 1993. Schwartz had been central to characterising LQTS clinically since the 1970s and created this diagnostic framework before the KCNQ1 and HERG genes were identified (1995/1996). The score was designed as a standardised probability tool for the pre-genetic test era.
Legacy in the Genomic Era
Despite the availability of genetic testing, the Schwartz Score remains highly relevant because 20–25% of clinically diagnosed LQTS patients have negative genetic testing (genotype-negative phenotype-positive). The score supports clinical decision-making in these cases and helps direct therapy without relying solely on molecular confirmation. It was updated by Schwartz himself in 2011 to align with modern LQTS genotype-phenotype data.
