QT interval - normal values during recovery from exercise

CIRCEP.110.961094
Published online before print May 23, 2011

The QT and Corrected QT Interval in Recovery After Exercise in Children

Wouter Rudolph Berger, Robert M. Gow, Suleman Kamberi, Michael Cheung, Katherine Rose Smith and Andrew Mark Davis

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/QTc in the recovery phase after exercise in children.

Methods and Results—Ninety-four volunteer boys and girls aged 8 to less than 17 years, without any history of heart disease underwent exercise testing and had 12 lead ECGS 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 to Q line. The recovery QT was maximally short at 1 minute of recovery in 93/94 individuals, then lengthened and stabilized at 4 to 5 minutes recovery. The recovery QT lengthens as HR decreases in an approximately linear fashion with a mean increase of 15 milliseconds per 10 beat decrease in heart rate. The 98th percentiles for the QTc using the Bazett formula during minutes 4 to 6 in recovery were from 482 msec to 491 msec. There was excellent intra-observer and inter-observer reliability with intra-class correlation coefficients of 0.95 and 0.88 respectively.

Conclusions—There is substantial individual variability of the normal repolarization process in the post-exercise 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.