[Physiological significance and normative parameters of rate adaptation of QT-interval during holter monitoring in healthy persons of young age].

Aim of the investigation consisted in to study parameters of " QT-dynamics " in healthy children and adolescents. We examined 26 children aged 7 - 17 years (mean 11,6 +/- 7 years) - 7 girls (9,3 +/- 2,3 years) and 19 boys (12,5 +/- 3,6 years). Holter monitoring with manual and automatic estimation of QT and QTc intervals. Dynamics of magnitude of QT interval was determined with the use of equation of linear regression Y = aX+b, where aX - coefficient of linear regression QT/RR (slope QT/RR), b - shear coefficient (intercept QT/RR). Values of QT interval at automatic analysis were 368,8 +/- 18,04 (340 - 410) ms for absolute QT and 424 +/- 14,99 (390 - 450) ms - for QTc, 289,4 +/- 14,6 (260 - 320). Mean values of " QT dynamics " were for slope QT/RR: 0,18 +/- 0,03 (0,13 - 0,24) for 24 hours, 0,16 +/- 0,03 (0,10 - 0,22) for daytime period, and 0,11 +/- 0,13 (0,05 - 0,18) for night time period; for intercept: QT/RR - 230,4 +/- 20,7 (192 - 282) for 24 hours, 299 +/- 25,5 (258 - 364) for day time period, and 242,7 +/- 21,8 (204 - 295) for night time period. Coefficient of correlation of intervals QT and RR (r QT/RR) was 0,79 +/- 0,05 (0,69 - 0,89) for 24 hours; 0,68 +/- 0,07 (0,52 - 0,82) for day time period, and 0,52 +/- 0,13 (0,19 - 0,74) for night time period. All values of " QT-dynamics " significantly differed from each other during various periods of day (p < 0,05). Negative relation was noted between 24 hour slope and intercept QT/RR (r= -0,88, p < 0,05), diurnal (r= -0,87, p < 0,05) and nocturnal slope and intercept QT/RR (r= -0,72, p < 0,05), positive relation was noted between 24 hour values of slope QT/RR and QT (r=0,49, p < 0,05), and intercept QT/RR with absolute QT (r=0,41, p < 0,05). Significantly higher values (p < 0,01) of slope QT/RR were in girls. Thus, increase of slope QT/RR is noted during augmentation of tone of sympathetic part of vegetative nervous system, lowering - when vagal influences are also enhanced. Intercept QT/RR appears to be combination parameter, increase of which reflects both lengthening of absolute mean value of QT interval and reciprocal nocturnal lowering of the slope parameter. It is necessary to assesses clinical and diagnostic significance of changes of novel parameters of " QT-dynamics " on the basis of normative sexual-aging values and physiological mechanisms, determining their variability.