Heart rate influences on repolarization duration and morphology in symptomatic versus asymptomatic KCNQ1 mutation carriers.

QT and Tp/Te intervals were longer in patients with LQT1 (n = 67) than in nonaffected subjects (n = 52) but did not differentiate symptomatic (n = 21) from asymptomatic patients (n = 46). At fast heart rate, the time to accumulate the last part of total T-wave area (the t50-97 interval) was longer in symptomatic carriers compared with asymptomatic patients (119 ± 19 vs 106 ± 15 ms, p