Normative data for QT/QTc in the recovery phase after exercise in children

  • Wouter Berger, Universitair Medisch Centrum Groningen/Royal Children's Hospital Melbourne, The Netherlands
  • Suleman Kamberi, The Royal Children's Hopsital, Australia
  • Vanessa Connell, The Royal Children's Hopsital, Australia
  • Ivan Macciocca, The Royal Children's Hopsital, Australia
  • Michael Cheung, The Royal Children's Hopsital Melbourne/ Murdoch Children's Research Institute, Australia
  • A/Prof Andrew Davis, The Royal Children's Hopsital, Australia

    • Congenital long QT syndrome (LQTS) is an enigmatic disease that can be difficult to diagnose. Examination of repolarisation in the recovery phase of exercise enhances diagnostic accuracy. There is however no normative data available for children.

    Objective
    To establish normative data for QT/QTc in children in the recovery phase of exercise.

    Methods
    Bicycle exercise testing was performed by 88 volunteers, aged 8-17. 12 lead monitoring was continued for 10 minutes into recovery. Four consecutive QT and preceding RR intervals were measured in lead II by a standardized manual method under magnification and averaged for each minute of recovery.QTc was calculated using Bazett’s formula. In addition four consecutive QT intervals in V5 were measured and averaged at recovery heart rates of 100/110/120 and 130.

    Results
    QTcII for the first 10 minutes of recovery and QTV5 at HR 100-130 are shown in table. Maximum QTcII was at 4-7 minutes. During the first 2 minutes of recovery females had a longer QTc: 0.43 vs 0.41 at 1 minute (p < 0.0005) and 0.44 vs 0.43 at 2 minutes (p < 0.05), thereafter there was no significant difference. Younger volunteers (8-12) had a significantly shorter QTc at 1 minute: 0.41 vs 0.43 and therafter there was no significant difference.

    Conclusions
    Normative data for QT/QTc will enhance diagnostic accuracy for LQTS in childhood.

    Minute/s of recovery QTc II (seconds) mean ±SD Heart rate QTV5 (seconds) mean ±SD
    1 0.42 ±0.02 100 0.33 ±0.02
    2 0.43 ±0.02 110 0.32 ±0.01
    3 0.44 ±0.02 120 0.30 ±0.02
    4-7 0.45 ±0.02 130 0.28 ±0.01
    8-10 0.44 ±0.02