Methods
This cross-sectional study enrolled 54 genetically identified LQTS patients (29 LQT1 and 25 LQT2) recruited from 3 medical institutions. The QT-apex (QTa) interval and the QT-end (QTe) interval at each 15-second were plotted against the R-R intervals and the linear regression (QTa/RR and QTe/RR slopes, respectively) were calculated from the entire 24-hour and separately during the day or night-time periods of the Holter recordings.