Body size influences heart rate in children aged 6 to 18 years old

Previous research established age-related normal limits for children's heart rates (HRs). However, children of the same age can have significantly different HRs, depending on whether they are overweight or underweight, tall or short. Studies on children HR have failed to find a clear correlation between HR and body size. The goal of our study was to create Z scores for HR based on weight (W), height (H), body mass index (BMI), and body surface area (BSA) and compare them to normal age-related HR limits. Electrocardiograms were recorded from a total of 22,460 healthy children ranging in age from 6 to 18 years old using BTL machines. A comparison was made between different age groups, in function of W, H, BMI, and BSA, based on the HR that was automatically detected by using the digitally stored electrocardiogram. Z scores were computed for each of the categories that were mentioned. Incremental Z score values between -2.5 and 2.5 were calculated to establish upper and lower limits of HR. The BSA's estimation of HR is the most accurate of the available methods and can be utilized with accuracy in clinical practice. Z scores for HR in children differ in function of the age, W, H, BMI and BSA. The best estimation is based on BSA. The novelty of our study is that we developed Z scores for HR in relation to body size, age and sex, producing a standardized, consistent, and reproducible result without requiring practitioners to learn and remember cutoff values for a wide range of variables across age groups and sexes. Z scores minimize observer and institutional bias, hence generating uniform and reproducible standards.