Normal Heart rate Value for Children by Age: ) median (2nd percentile, 98th percentile ) Limits of variation in heart rate and QT interval among 5,632 healthy children aged 0 to 18 M. Shkolnikova, I. Miklashevich, L. Kalinin Moscow research institute of pediatrics and children’s surgery Moscow, Russian Federation The basic principles of interpretation of the ECG in children are identical to those in adults, but the progressive changes in anatomy and physiology which take place between birth and adolescence result in some features which differ significantly from the normal adult pattern and vary according to the age of the child. Correct interpretation of the ECG is therefore potentially difficult and a detailed knowledge of these age dependent changes is critically important if errors are to be avoided. The prognostic value of ECG depends on their normal ranges of values the appropriate ECG intervals. The study aims at obtaining of the clinically relevant normal limits for the paediatric ECG in population of Russian children. The study evaluates relationship between the QT-interval and the heart rate in a large representative sample of healthy children in Russia. The study design -The results were obtained from the ECG records of 5,632 children (2,871 boys and 2,761 girls) aged from 0 to 18 years participating in epidemiological study on ECG in children carried out during the period from to Thirteen regions of the Russian Federation were randomly selected for Russian National ECG Screening Program (RNESP). All children underwent a physical examination and were included in the study only if no disease was found. Standard resting 12-lead electrocardiograms were acquired using a Schiller AT-1 three-channel recorder at 25 mm\s and 1mV:10 mm. All ECGs were read and coded by twelve trained cardiologists on the basis of Minnesota code criteria. Ordinary least squares regression was used to estimate relationship between the QT interval and independent variables. The latter included age, sex, and heart rate as reflected by RR interval. Conclusion - These new normal limits differ from those commonly used and suggest that diagnostic criteria for the paediatric ECG should be adjusted Study Population Total 5632 children aged from 0 to 18 years Members of the RNESP Age groups Results - The normal limits of all clinically relevant ECG measurements were determined for twelve age groups: 0-7 days, 3 week-3 months, 4-6, 7-9, months, 1-18 years. Median values are given together with the 98th percentiles, taken as the upper limits of normal. The 2nd percentiles, taken as the lower limits of normal. Normal limits are presented separately for boys and furls. Clinically significant differences were shown to exist, compared with previously established normal limits. Sex differences could be demonstrated for heard rate and QRS axis. For children at ages from 0 to 4 (1,792 observations), the regression analysis revealed linear relationship between of QT interval, RR interval and age. In this age group, QT values are only weakly associated with sex and this link can be neglected. For children at ages from 5 to 17 (2,623 observations), there is a significant quadratic relationship between QT and RR, while links with age and sex are statistically insignificant. QT tends to stabilize when heart rate becomes slow. For age 0-4, we produced a reference table giving mean QT and 5th and 95th percentiles depending on age and RR interval. For age 5-17, the equivalent table provides the same values depending on RR only. The study was supported by “Schiller AG” AGEMALEFEMALETOTAL 0-7 days week-3 month month month month years years years years years years years years years years years years years years years Age0-7 days1 week-3 m4-6 month 7- 9month month 1 y2 y3 y4 y5 y6 y7 y8 y9 y10 y11 y12 y13 y14 y15-18 male139 (86-181) 150 ( ) 131 (76-160) 127 (88-177) 120 (69-197) 120 (63-195) 111 (71-150) 102 (79-128) 98 (73-128) 92 (70-115) 91 (67-120) 88 (64-125) 85 (62-125) 83 (61-110) 80 (57-117) 76 (52-110) 76 (57-115) 77 (54-108) 78 (54-115) 72 (51-111) female139 (96-185) 150 ( ) 136 (89-188) 129 (90-200) 125 (75-186) 127 (69-188) 115 (88-172) 103 (62-167) 98 (75-128) 94 (71-136) 91 (70-120) 89 (67-126) 88 (64-131) 83 (60-125) 80 (62-115) 84 (64-127) 84 (53-115) 79 (59-113) 82 (58-118) 77 (57-110) Figure 2Continuous RR-dependent percentile curves of the QT for children aged 0-18 Figure 1Percentile curves of the QT by heart rate for children aged Figure 3Percentile curves of the QTc by heart rate for children aged 0-18.