Repolarization analysis in children with the long QT syndrome.

QT duration changes were analysed in 26 children with long QT syndrome (median age 9 years). With 12-lead Holter recordings, we found that macroscopically QT adaptation to heart rate changes was slow and only 3 of 26 patients showed abrupt changes in QT interval duration. These changes in the time domain were always accompanied by changes of STT morphology in the 3 of 26 patients. Application of Bazett's heart rate correction algorithm was inappropriate to show true QT changes in this young patient group due to temporary typical large cycle length variations, where moreover an overcorrection of the heart rate impact resulted in reflection of RR interval changes rather than true QT duration changes.