Reproducibility of corrected QT interval in pediatric genotyped long QT syndrome

Reproducibility of corrected QT interval ( QT c), especially QT c after exercise, has not been thoroughly investigated. We reviewed charts of pediatric patients who underwent treadmill‐exercise stress testing without medication multiple times within 1 year. In patients with long‐ QT syndrome ( LQTS ; n = 22), the discrepancy in QT c between two treadmill exercise stress tests using Fridericia's formula was 14 ± 12 ms at rest, 13 ± 12 ms 4 min after exercise, with a maximum of 14 ± 12 ms after exercise. There was no statistically significant difference in QT c between the two tests. Intraclass correlation coefficients ( ICC ) were 0.84, 0.85, and 0.85, respectively. In controls (n = 13), the discrepancy in QT c was 18 ± 12 ms at rest, 14 ± 7 ms 4 min after exercise, with a maximum of 14 ± 9 ms after exercise. There was no significant difference in QT c between the two tests. ICC were 0.78, 0.80, and 0.80, respectively. QT c calculated using Bazett's formula also showed high reproducibility. Reproducibility of QT c in children is high at rest and after exercise.