Effect of age and overweight on the QT interval and the prevalence of long QT syndrome in children

The change in QT interval with age during childhood of normal children and children with long QT syndrome (LOTS) and the effects of body mass index on the QT interval have not been studied in detail. The prevalence of LOTS in children is not well known. We measured 3 consecutive QT and RR intervals in 4,655 children. Their electrocardiograms along with their height and weight were recorded when they were in the first grade in 1994 and again when they were in the seventh grade in 2000. The QT interval was corrected by Bazett's formula. The longer corrected QT intervals in female subjects than male subjects start at elementary school age, earlier than previously reported. Overweight did not have an impact on the uncorrected or corrected QT interval. None of the 4 children diagnosed with LOTS in the seventh grade had characteristic electrocardiographic findings of LOTS in the first grade. All 4 are nonfamilial cases. The prevalence of LOTS in children was found to be 1 of 1,164. These data suggest that abnormal electrocardiographic phenotypes in children with nonfamilial LOTS may appear during the elementary school year. The longer QT intervals in female subjects than male subjects start at the same period. No correlation was found between obesity and length of the QT interval. Finally, the prevalence of LOTS in children is greater than previously suspected. (C) 2002 by Excerpts Medica, Inc.