LQTS: Difference between revisions

==Diagnosis==

===General===

*The diagnosis is by measurement of the heart rate corrected QT interval on the ECG, which can be calculated with the [[QTc calculator]].  

*Sometimes the QT interval can be difficult to assess. Read the [[guidelines for measurement of difficult QT interval]].  

==Acquired LQTS==

Acquired LQTS is most often caused by drugs that prolong the QT interval; combined with risk factors the risk of [[Torsade de Pointes]] is likely to increase.  

==Congenital LQTS==

The prevalence of congenital LQTS is about 1:3000-5000. More than 10 different types of congenital LQTS have been described. However, only LQTS 1-3 are relatively common. <cite>ACC2006</cite>

The three most common forms of LQTS can be recognized by the characteristic clinical features and ECG abnormalities.

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!LQTS type

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Before the genes involved were known, some syndromes associated with a prolonged QT interval on the ECG had been described earlier:

Diagnosis of LQTS is established by prolongation of the QTc interval in the absence of specific conditions known to lengthen it (for example QT-prolonging drugs) and/or molecular genetic testing of genes associated with LQTS.  

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!colspan="4"|Diagnostic criteria by Schwartz et al.

|colspan="4"|''Total score =1 Low probability; 1.5-3 Intermediate probability; =3.5 High probability''

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The prolonged QT interval can cause torsade de pointes, which is usually self-terminating, thus causing a cardiac syncopal event. The mean age of onset of symptoms (syncope or sudden death) is 12 years and earlier onset is usually associated with more severe form of the disease. In LQTS type 1, cardiac symptoms are often precipitated by exercise; especially swimming is notorious for life-threatening cardiac events. In LQTS type 2, arrhythmogenic triggers are adrenergic; especially nightly noise (such as the morning alarm clock or nightly thunderlightening) is known to cause life-threatening cardiac events. On the other hand, in LQTS type 3, QT prolongation and possibly subsequent torsade de pointes is precipitated by bradycardia.  

===ECG tests===

ECGs can be difficult because there is a considerable overlap between the QT interval of affected and unaffected individuals.

==Genetic diagnosis==

Today, 13 LQTS genes associated with LQTS have been identified. Most commonly, KCNQ1, KCNH2 and SCN5A, which are associated with LQTS type 1, type 2 and type 3 respectively, are found. Other, less frequently involved genes are displayed the table below.  

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!LQTS type

|Type 1

|KCNQ1

|607542

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|600734

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There is an important genotype-phenotype relationship on severity of the disease. In genotype–phenotype studies in the Rochester LQTS registry it was shown that in both LQTS type 1 and type 2, mutation locations and the degree of ion channel dysfunction caused by the mutations are important independent risk factors influencing the clinical course of this disorder.

==Risk Stratification==

Gene-specific differences of the natural history of LQTS have also been demonstrated and allow genotype-based risk stratification. Indeed, QT interval duration, gender and genotype (including mutation location and degree of ion channel dysfunction) are significantly associated with the outcome, with a QTc interval >500ms, and a LQT2 or LQT3 genotype determining the worst prognosis. Gender differently modulates the outcome according to the underlying genetic defect: the LQT3 males and LQT2 females are the highest risk subgroups. Risk stratification is best done by an expert cardio-genetics cardiologist.

==Treatment <cite>ACC2006</cite>==

===Lifestyle modification===  

*No competitive sports in all LQTS patients  

   

==References==

<biblio>

#Schwartz2001 pmid=11136691