What are the diagnostic criteria for long QT syndrome (LQTS)?

Updated: Nov 29, 2017
  • Author: Ali A Sovari, MD, FACP, FACC; Chief Editor: Mikhael F El-Chami, MD  more...
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Answer

A presentation with syncope or sudden cardiac death, in combination with a long QT interval on an ECG, typically suggests long QT syndrome (LQTS) and leads to genetic testing to diagnose the disease. In many patients, however, the presentation may not be typical. Therefore, other tests may be indicated.

Schwartz et al suggested diagnostic criteria for LQTS in 1993 that still serve as the best criteria for clinicians. [20] In their model, the criteria are divided to three main categories, as shown in Table 2, below. The maximum score is 9—A score above 3 indicates a high probability of LQTS.

Table 2. Diagnostic Criteria for LQTS (Open Table in a new window)

Criterion

Points

Electrocardiogram findings *

QTc, ms

>480

3

460-469

2

450-459 in male patient

1

Torsade de pointes

2

T-wave alternans

1

Notched T wave in 3 leads

1

Low heart rate for age§

0.5

Clinical history

Syncope

With stress

2

Without stress

1

Congenital deafness

0.5

Family history 

 

A. Family members with definite LQTS#

1

B. Unexplained sudden cardiac death at age <30 years in an immediate family member

0.5

LQTS = long QT syndrome.

*In the absence of medications or disorders known to affect these electrocardiographic features.

QTc calculated by Bazett's formula.

Mutually exclusive.

§Resting heart rate below the second percentile for age.

||Mutually exclusive.

The same family member cannot be counted in both A and B.

#Definite LQTS is defined by an LQTS score above 3 (≥4).


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