The QT and corrected QT interval in recovery after exercise in children.

BACKGROUND Prolongation of the QT interval after exercise can be used to help diagnose long-QT syndrome, especially when the resting QT interval is borderline. The aim of this study was to determine the normal ranges for QT and corrected QT in the recovery phase after exercise in children. METHODS AND RESULTS Ninety-four volunteer boys and girls aged 8 to < 17 years without any history of heart disease underwent exercise testing and had a 12-lead ECG performed in the supine position for 10 minutes of recovery. The QT was measured using a standardized tangent method, with the baseline defined as the Q-Q line. The recovery QT was maximally short at 1 minute of recovery in 93 of 94 children then lengthened and stabilized at 4 to 5 minutes recovery. The recovery QT lengthens as heart rate decreases in an approximately linear fashion with a mean increase of 15 ms per 10-beat decrease in heart rate. The 98 th percentiles for the corrected QT using the Bazett formula during minutes 4 to 6 in recovery were from 482 to 491 ms. There was excellent intraobserver and interobserver reliability, with intraclass correlation coefficients of 0.95 and 0.88, respectively. CONCLUSIONS There is substantial individual variability of the normal repolarization process in the postexercise recovery period in children. The study provides a reference for normal responses for similar populations using a specific measurement protocol that can be easily applied.