Background: Clinical management in long QT syndrome (LQTS) can be guided by comprehensive phenotyping, knowledge of the associated genetic variant, and risk-beneft ratio of different treatment strategies. Objective: To describe varying management strategies in a patient with LQTS. Methods: N/A Results: A 4 year old boy was diagnosed with LQTS after syncope while swimming. Genetic testing exposed a truncating Swedish founder mutation in the C-terminal of KCNQ1 (p.R518X). He was treated with nadolol and remained asymptomatic. Aged 11 the QTc at rest was 407ms, and in the recovery period of exercise within normal limits (fg 1a). He suffered an acute psychotic reaction with suicidal ideation, necessitating nadolol discontinuation. A repeat exercise test off therapy unmasked a LQTS phenotype (max QTc 520ms; fg 1b). Detailed assessment included age, sex, genotype, risk of further cardiac events, the need for QT prolonging agents, and further psychosis/suicide risk. Given the phenotypic expression off nadolol and prior symptoms he underwent left cardiac sympathetic denervation (LCSD) and started the QT prolonging agent escitalopram. Subsequent QTc on exercise test was again within normal limits (fg 1c). He remains asymptomatic 15 mos later, on a diminishing dose of escitalopram. Conclusion: Typically heterozygous carriers of KCNQ1 R518X display a mild/absent phenotype, however, this can be affected by multiple individual factors. In this complex situation of competing risks comprehensive phenotyping and detailed knowledge of the underlying genetic variant guided successful management.
Hylind, R. J., Ladouceur, V. B., Fynn-Thompson, F., Hourigan, S. E., Bezzerides, V. J., & Abrams, D. J. (2018). Genotype-phenotype-guided medical and surgical intervention in long QT syndrome. HeartRhythm Case Reports, 4(1), 14–17. https://doi.org/10.1016/j.hrcr.2017.09.001