Table 2.
LQTS diagnostic criteria [from Schwartz and Crotti (25)].
| Points | |
|---|---|
| Electrocardiographic findingsa | |
| A. QTcb | |
| ≥480 ms | 3 |
| 460–479 ms | 2 |
| 450–459 ms (in males) | 1 |
| B. QTcb fourth minute of recovery from exercise stress | |
| Test ≥480 ms | 1 |
| C. Torsade de pointesc | 2 |
| D. T wave alternans | 1 |
| E. Notched T wave in 3 leads | 1 |
| F. Low heart rate for aged | 0.5 |
| Clinical history | |
| A. Syncopec | |
| With stress | 2 |
| Without stress | 1 |
| B. Congenital deafness | 0.5 |
| Family history | |
| A. Family members with definite LQTSe | 1 |
| B. Unexplained sudden cardiac death below 30 years of age among immediate family memberse | 0.5 |
aIn the absence of medications or disorders known to affect these electrocardiographic features.
bQTc calculated by Bazett’s formula where QTc = QT/√RR.
cMutually exclusive.
dResting heart rate below the second percentile for age.
eThe same family member cannot be counted in A and B.
Score: ≤1 point: low probability of LQTS; 1.5–3 points: intermediate probability of LQTS; ≥3.5 points high probability.