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Key Points

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  • Disease summary:

    • Inherited channelopathy characterized by elongated QT intervals on electrocardiogram (ECG), caused by delayed ventricular repolarization in the myocyte.

    • Increased propensity to syncope, polymorphous ventricular tachycardia (torsade de pointes), T-wave abnormalities, and sudden death. Unexplained seizures can also be an atypical presentation.

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  • Family history (in addition to above characteristics):

    • Sudden cardiac death

    • Sudden infant death syndrome

    • Congenital deafness

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  • Hereditary basis:

    • LQTS exhibits predominantly autosomal dominant inheritance, meaning there is a 50% chance of a child inheriting the disease causing mutation from a parent.At least 12 genes have been implicated in LQTS, though the majority families have a mutation in KCNQ1, KCNH2 and SCN5A which cause LQT1, LQT2, and LQT3, respectively.There is variability of expression, even amongst family members with the same mutation.

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  • Differential diagnosis:

    • It is important to distinguish the hereditary forms of the syndrome from environmental (acquired) causes including QT interval prolonging therapies (ie, antiarrhythmic agents), myocardial ischemia, alternative cardiomyopathies, hypocalcemia and hypothyroidism.

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Diagnostic Criteria and Clinical Characteristics

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Diagnostic Criteria for Long QT Syndrome

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Table Graphic Jump Location
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Allelic Differential Diagnosis

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  • Jervell and Lange-Nielsen syndrome (JNLS): characterized by congenital sensorineural hearing loss and long QTc interval, inherited in an autosomal recessive manner (KCNQ1 or KCNE1)

  • Brugada syndrome: characterized by rapid polymorphic ventricular tachycardia or ventricular fibrillation and sudden death, inherited in an autosomal dominant manner (SCN5A).

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Differential Diagnosis

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  • Timothy syndrome (LQTS with syndactyly): characterized by cardiac abnormalities (LQTS and/or structural defects), variable syndactyly of fingers or toes, facial anomalies and neurologic symptoms (autism, seizures, mental retardation), caused by de novo alterations in CACNA1C.

  • Andersen-Tawil syndrome (ATS): characterized by muscle weakness, ventricular arrhythmias, prolonged QT interval, facial and limb anomalies, caused by alterations in KCNJ2.

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Screening and Counseling

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Screening

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The hallmark for screening patients for LQTS is the ECG by establishing evidence for QTc prolongation and examining the T-wave morphology (LQT1 broad T waves, LQT2 bifid T waves, LQT3 peaked and biphasic T waves). It is important to recognize that a normal ECG does not rule out the possibility of LQTS. If the clinical suspicion is strong, either because of a family history or consistent clinical symptoms, repeat ECG ...

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