Schwartz et al updated the criteria for the long QT syndrome in 1993. This can help diagnose a patient with the idiopathic long QT syndrome.
Patient preparation: The patient must not be taking a medication known to prolong the QT interval. A person should not be evaluated while suffering from a condition affecting the QT interval.
Parameters:
(1) clinical history of syncope
(2) clinical history of congenital deafness
(3) definite family history of long QT syndrome
(4) unexplained sudden death in an immediate family member not included in #3
(5) long corrected QT interval on ECG
(6) torsade de pointes
(7) T wave alternans
(8) notched T wave in 3 leads
(9) low heart rate for age
|
Parameter |
Finding |
Points |
|
clinical history of syncope |
none |
0 |
|
|
without stress |
1 |
|
|
with stress |
2 |
|
congenital deafness |
absent |
0 |
|
|
present |
0.5 |
|
family history of long QT syndrome |
absent |
0 |
|
|
present |
1 |
|
unexplained sudden death in an immediate family member before age 30 |
absent |
0 |
|
|
present |
0.5 |
|
corrected QT interval |
< 450 msec |
0 |
|
|
450 msec (in males) |
1 |
|
|
460-470 msec |
2 |
|
|
>= 480 msec |
3 |
|
torsade de pointes |
absent |
0 |
|
|
present |
2 |
|
T wave alternans |
absent |
0 |
|
|
present |
1 |
|
leads with notched T waves |
>= 3 |
1 |
|
|
< 3 |
0 |
|
heart rate for age |
low (< 2nd percentile for age) |
0.5 |
|
|
not low |
0 |
where:
• Torsade de pointes and syncope are mutually exclusive.
• The same family member cannot be used to satisfy a family history of LQTS and sudden death.
• The heart rates for age in children are given by Davignon et al (1980).
• The ranges for corrected QT interval given in the original table do not cover a number of situations: (a) female with interval 450 msec; (b) range 451-459; (c) range 471-479. I have set (a) to 0 points; (b) to 1 point; (c) to 2 points in the implementation.
total score =
= MAX((points for syncope), (points for torsade on ECG)) + SUM(points for remaining parameters)
Interpretation:
• minimum score: 0
• maximum score: 9.5
|
Total Score |
Probability of LQTS |
|
<= 1 |
low |
|
2 to 3 |
intermediate |
|
>= 4 |
high |
where:
• This scheme leaves out scores 1.5 and 3.5. In the implementation I have made 1.5 to 3.5 as intermediate risk.
Specialty: Cardiology
