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LQTS: Difference between revisions
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The '''Long QT Syndrome (LQTS)''' refers to a condition in which there is an abnormally long QT interval on the ECG. This was first recognized by Dr. Jervell and Dr. Lange-Nielsen in 1957. They described 4 children with a long QT interval which was accompanied by hearing deficits, sudden cardiac death and an autosomal recessive inheritance. <cite>Lang1957</cite> | The '''Long QT Syndrome (LQTS)''' refers to a condition in which there is an abnormally long QT interval on the ECG. This was first recognized by Dr. Jervell and Dr. Lange-Nielsen in 1957. They described 4 children with a long QT interval which was accompanied by hearing deficits, sudden cardiac death and an autosomal recessive inheritance. <cite>Lang1957</cite> | ||
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The three most common forms of LQTS can be recognized by the characteristic clinical features and ECG abnormalities. | The three most common forms of LQTS can be recognized by the characteristic clinical features and ECG abnormalities. | ||
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!LQTS type | !LQTS type | ||
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|'''ECG''' | |'''ECG''' | ||
| | |''Early onset'' | ||
broad based T wave | |||
|Small late T wave | |Small late T wave | ||
| | |''Late onset'' | ||
T wave with normal configuration | T wave with normal configuration | ||
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|'''Eponyme''' | |'''Eponyme''' | ||
|If condition is homozygous: Jervell and Lange-Nielsen syndrome 1 | |If condition is homozygous: | ||
|If condition is homozygous: Jervell and Lange-Nielsen syndrome 2 | Jervell and Lange-Nielsen syndrome 1 | ||
|If condition is homozygous: | |||
Jervell and Lange-Nielsen syndrome 2 | |||
| | | | ||
|} | |} | ||
Before the genes involved were known, some syndromes associated with a prolonged QT interval on the ECG had been described earlier: | Before the genes involved were known, some syndromes associated with a prolonged QT interval on the ECG had been described earlier: | ||
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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. | 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"|Diagnostic criteria by Schwartz et al. | ||
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|colspan="4"|''Total score =1 Low probability; 1.5-3 Intermediate probability; =3.5 High probability'' | |colspan="4"|''Total score =1 Low probability; 1.5-3 Intermediate probability; =3.5 High probability'' | ||
|} | |} | ||
[[Image:Graph.jpg| | [[Image:Graph.jpg|thumb|400px|Various triggers for cardiac events have been identified among the different genotypes.]] | ||
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. | 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=== | ===ECG tests=== | ||
[[Image:Lqts1-3.png|right|thumb| | [[Image:Lqts1-3.png|right|thumb|400px|Various ECG patterns can be recognized among the different genotypes]] | ||
ECGs can be difficult because there is a considerable overlap between the QT interval of affected and unaffected individuals. | ECGs can be difficult because there is a considerable overlap between the QT interval of affected and unaffected individuals. | ||
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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. | 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 | !LQTS type | ||
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|Type 1 | |Type 1 | ||
|KCNQ1 | |KCNQ1 | ||
|KVLQT1 (I<sub>Ks< | |KVLQT1 (I<sub>Ks<sub>) | ||
|607542 | |607542 | ||
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|600734 | |600734 | ||
|} | |} | ||
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. | 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. | ||