Figure legends
Figure 1. QT measurement. (a) Consecutive sinus beats every 15 seconds were selected and averaged. (b) Signal averaged waveform. The QTe interval was defined as the time between the QRS onset and the point at which the isoelectric line intersected a line tangent to the maximal (or minimal) downslope of the positive (or negative) T-wave. The QTa interval was defined as the time between the QRS onset and the T wave’s apex (or nadir).(c) This process was repeated every 15 seconds.
Figure 2. Representative the trend of QT interval along with the 24- hour study in each group. QT trend graph of the LQT2 showed that QT prolongation was more prominent in the night time.
Figure 3. Representative QTa/RR, QTe/RR, QTe-QTa/RR slopes from entire 24-hour Holter recordings in the LQT1 and LQT2 patients. QTa/RR and QTe/RR slopes were steeper in the LQT2 patient than that of the LQT1 patient.
Figure 4. Representative QTa/RR, QTe/RR, and QTe-QTa/RR slopes from daytime Holter recordings in the LQT1 and LQT2 patients. QTa/RR and QTe/RR slopes were steeper in the LQT2 patient than that of the LQT1 patient.
Figure 5. Representative QTa/RR, QTe/RR, QTe-QTa/RR slopes from night time Holter recordings in the LQT1 patients and LQT2 patients. Although QTa/RR slope was steeper in the LQT2 patient than that of the LQT1 patient, the degree was lower than that from entire 24-hour or daytime Holter recordings.
Figure 6. The receiver operating characteristic (ROC) curve analysis showed an optimal cutoff point of 0.211 of QTa/RR slope from entire 24-hour Holter recordings, with 80.0% sensitivity, 75.0% specificity, and an area under the curve of 0.804 (95% confidence interval, 0.68-0.93).