Diagnostic criteria for long QT syndrome (the Schwartz score)
| Diagnostic criteria | Points | ||
| ECG findings | QTc calculated by Bazett's formula* | ≥480 ms | 3 |
| 460–470 ms | 2 | ||
| 450 ms (males) | 1 | ||
| Torsades de pointes† | 2 | ||
| T wave alternans | 1 | ||
| Notched T wave in three leads | 1 | ||
| Resting heart rate below second centile for age | 0.5 | ||
| Clinical history | Syncope† | With stress | 2 |
| Without stress | 1 | ||
| Congenital deafness | 0.5 | ||
| Family history‡ | Family members with definite LQTS by Schwartz score | 1 | |
| Immediate family members with SCD <30 years old | 0.5 |
Score ≤1, low probability of LQTS; 2–3, intermediate probability of LQTS; ≥4, high probability of LQTS.
↵* In the absence of drugs or disorders known to affect QTc.
↵† Mutually exclusive.
↵‡ The same family member cannot be counted in both family history categories.
LQTS, long QT syndrome; QTc, corrected QT interval; SCD, sudden cardiac death.