Evaluation of systolic time intervals in a group of healthy children 10-12 years old.

The normal values of the systolic time intervals (STI) in children and their possible relationship with heart rate have not been studied thoroughly. From a group of 9760 healthy school-children 10-12 years old, 488 subjects of both sexes were randomly selected in order to measure the STI and calculate the respective indices. The final population study was composed of 479 children, 249 males and 230 females, aged from 10/1 to 12/2 years/months (mean age 11/1 +/- 0/4 years/months). In each child, the following STI were measured: total electromechanical systole (Q-S2), left ventricular ejection time (LVET), mechanical systole (S1-S2), preejection period (PEP), PEP/LVET ratio and isovolumic contraction time (ICT). For each parameter, the regression equation with heart rate was calculated using a linear model and was verified if a real difference existed between linear regressions of males and females. Moreover, for each parameter, the index from the respective regression equation was calculated as well as its normal value and the standard deviation. Finally, the diastolic time (% diastole) and its correlation with heart rate were calculated. Our results demonstrate that in children, a close correlation exists between the STI and heart rate, although less striking than in adults; only the PEP/LVET ratio appears independent from heart rate, as in adults. The % diastole versus heart rate non-linear relationship shows the same behaviour as in adults. Finally, in agreement with other authors, our results show that in childhood the relationship between the STI and heart rate behaves alike in males and females.