Author(s): Shimizu W, Horie M, Ohno S, Takenaka K, Yamaguchi M,
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Abstract OBJECTIVES: We sought to compare the arrhythmic risk and sensitivity to sympathetic stimulation of mutations located in transmembrane regions and C-terminal regions of the KCNQ1 channel in the LQT1 form of congenital long QT syndrome (LQTS). BACKGROUND: The LQT1 syndrome is frequently manifested with variable expressivity and incomplete penetrance and is much more sensitive to sympathetic stimulation than the other forms. METHODS: Sixty-six LQT1 patients (27 families) with a total of 19 transmembrane mutations and 29 patients (10 families) with 8 C-terminal mutations were enrolled from five Japanese institutes. RESULTS: Patients with transmembrane mutations were more frequently affected based on electrocardiographic (ECG) diagnostic criteria (82\% vs. 24\%, p < 0.0001) and had more frequent LQTS-related cardiac events (all cardiac events: 55\% vs. 21\%, p = 0.002; syncope: 55\% vs. 21\%, p = 0.002; aborted cardiac arrest or unexpected sudden cardiac death: 15\% vs. 0\%, p = 0.03) than those with C-terminal mutations. Patients with transmembrane mutations had a greater risk of first cardiac events occurring at an earlier age, with a hazard ratio of 3.4 (p = 0.006) and with an 8\% increase in risk per 10-ms increase in corrected Q-Tend. The baseline ECG parameters, including Q-Tend, Q-Tpeak, and Tpeak-end intervals, were significantly greater in patients with transmembrane mutations than in those with C-terminal mutations (p < 0.005). Moreover, the corrected Q-Tend and Tpeak-end were more prominently increased with exercise in patients with transmembrane mutations (p < 0.005). CONCLUSIONS: In this multicenter Japanese population, LQT1 patients with transmembrane mutations are at higher risk of congenital LQTS-related cardiac events and have greater sensitivity to sympathetic stimulation, as compared with patients with C-terminal mutations.
This article was published in J Am Coll Cardiol
and referenced in Journal of Bioequivalence & Bioavailability