[Assesment of Parameters of QT Interval in Children and Adolescents.]

Aim. To determine limits of interval QT in children and adolescents aged 0-17 years and to detect possible ethnic differences of its changes. Material and Method. Twelve lead ECGs were recorded in 1531 subjects without overt cardiovascular pathology (47.2% females, 52.8 males, 57.3% of Slavic and 42.7% of Buryat i.e. mongoloid ethnicity). Results. Corrected QT interval (QTc) exceeded 440, 460 and 480 ms in 2.3, 1.05, and 0.26% of children. Prolongation of QTc was found in 0.46% and 0.11% of Slavic and Buryat children, respectively (p=ns). Starting from the age of 8 years girls had longer QTc than boys (454.1+/-15.2 and 438.3+/-8.4 ms, respectively, p<0.05). QTc less than 350 ms was registered in 12 children (0.78%). Eight of these children with mean QTc 329.1+/-32.3 ms had family history of syncope or sudden death. Variability of absolute QT values was 8+/-14.3 ms (maximally up to 40 ms). Conclusions. QT interval is prolonged when QTc duration exceeds 440 ms in children younger than 8 years and in male adolescents or 460 ms in girls aged 8 years or older and in children during first year of life. QT interval is shortened when QTc is less than 350 ms (1st degree of shortening). In children with QTc below 330 ms (2nd degree of shortening) short QT syndrome should be excluded. Normal variability of absolute QT value during sinus arrhythm on ECG at rest does not exceed 40 ms.