Long QT Syndrome

Description

  • Long QT syndrome (LQTS) is a cardiac electrophysiologic disorder, characterized by QT prolongation and T-wave abnormalities on the EKG that are associated with tachyarrhythmias.

  • The diagnosis of LQTS is established in a proband with one or more of the following:

    • A risk score of ≥3.5 in the absence of a secondary cause for QT prolongation

    • The presence of a corrected QT interval ≥500 ms in repeated EKGs in the absence of a secondary cause for QT prolongation

    • The identification of a in one of the genes known to be associated with LQTS 

How often is a hereditary cause identified?

  • There are known acquired and hereditary causes of LQTS. 

  • The main genes associated with LQTS are KCNQ1, KCNH2, and SCN5A, and contribute to approximately 75% of all cases.

  • There are additional genes identified that account for 5-10% of cases

  • Approximately 25% of individuals with LQTS will not have a genetic cause identified on genetic testing.

How does identifying a hereditary cause change a patient’s medical management?

  • Beta blocker medication is the primary treatment for LQTS

  • Possible implantable cardioverter-defibrillators (ICD) and/or left cardiac sympathetic denervation (LCSD) for those with beta-blocker-resistant symptoms, inability to take beta blockers, and/or history of cardiac arrest

  • Sodium channel blockers can be useful as additional pharmacologic therapy for patients with a QTc interval >500 ms (Alders et al, 2003).

How are these conditions inherited?

  • LQTS is usually inherited in an autosomal dominant pattern. There are rare causes of LQTS that are inherited in an autosomal recessive pattern.

Where can I learn more about Long QT Syndrome?

References

  • Ingles J, Semsarian C. Time to Rethink the Genetic Architecture of Long QT Syndrome. Circulation. 2020 Feb 11;141(6):440-443. doi: 10.1161/CIRCULATIONAHA.119.044760. Epub 2020 Feb 10. PMID: 32078431.

  • Alders M, Bikker H, Christiaans I. Long QT Syndrome. 2003 Feb 20 [Updated 2018 Feb 8]. In: Adam MP, Feldman J, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2023. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1129/