Table 2.
1993–2006 Long QT syndrome (LQTS) diagnostic criteria
| POINTS | |||
| ELECTROCARDIOGRAPHIC FINDINGS # | |||
| A | QTc^ | > 480 ms | 3 |
| 460 – 470 ms | 2 | ||
| 450 – 459 (male) ms | 1 | ||
| B | TORSADE DE POINTES * | 2 | |
| C | T WAVE ALTERNANS | 1 | |
| D | NOTCHED T WAVE IN 3 LEADS | 1 | |
| E | LOW HEART RATE FOR AGE @ | 0.5 | |
| CLINICAL HISTORY | |||
| A | SYNCOPE * | WITH STRESS | 2 |
| WITHOUT STRESS | 1 | ||
| B | CONGENITAL DEAFNESS | 0.5 | |
| FAMILY HISTORY $ | |||
| A | FAMILY MEMBERS WITH DEFINITE LQTS | 1 | |
| B | UNEXPLAINED SUDDEN CARDIAC DEATH BELOW AGE 30 AMONG IMMEDIATE FAMILY MEMBERS | 0.5 | |
# In the absence of medications or disorders known to affect these electrocardiographic features
^ QTc calculated by Bazett's formula where QTc = QT/√RR
* Mutually exclusive
@ Resting heart rate below the 2nd percentile for age
$ The same family member cannot be counted in A and B
SCORE: ≤ 1 point = low probability of LQTS
> 1 to 3 points = intermediate probability of LQTS
≥ 3.5 points = high probability of LQTS