Heart rate variability in healthy children and adolescents is partially related to age and gender☆
Introduction
Heart rate variability (HRV) is a useful tool that might provide indices of autonomic modulation of the sinus node [1]. A reduced HRV is a sign of autonomic imbalance, and is associated with increase of cardiac mortality and sudden death [1], [2], [3], [4], [5]; HRV seems to be useful also in heart transplantation [6], [7], [8]. In the pediatric age-group HRV has been investigated in diabetes [9], respiratory distress syndrome of the newborn [10], [11], [12] and sudden infant death syndrome [13], where a delayed or a reduced cardio–vagal development has been demonstrated [14]. Changes in heart rate and HRV can be measured by various techniques, and since these changes are autonomically mediated, these measurements may reflect autonomic tone. HRV data are generally obtained from studies in adults, and most of the published papers in adult and pediatric age compared small groups of patients with age-matched healthy controls. HRV is affected by age, but might also be influenced by gender. Measurement of time-domain variables of HRV is simple and practical, even in children. The aim of our study was to define the values of 24-h HRV in normal children and adolescents divided by age and gender.
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Materials and methods
We evaluated 103 subjects (57 males and 46 females), aged 1–20 years. Male subjects and female subjects were divided into eight groups, four for females and four for males, aged 1–5 years (1a and 1b, respectively), 6–10 years (2a–2b), 11–15 years (3a–3b), 16–20 years (4a–4b). Newborns were excluded.
Subjects were defined as healthy after a complete non-invasive cardiological examination, including physical examination, standard ECG, Doppler echocardiography, Holter monitoring and exercise test.
Results
The results are shown in Table 1. All the variables were normally distributed (Kolmogorov–Smirnov test). When age and sex models of each variable for interaction between age and sex were tested, no improvement was obtained; we then excluded interaction from further analysis.
Mean cycle length increased significantly through all age classes (P<0.0001) except in group 3 versus 4, and resulted significantly higher (lower HR) in males (P<0.007).
SDNN increased significantly through all age-groups (P
Discussion
HRV is usually evaluated by frequency-domain and by time-domain analysis [1], [18], by short- and by long-term recordings. Short-term recordings, performed under controlled and reproducible conditions [19], [20], may fail to detect long-term trends of diurnal influences in heart rate that have clinical importance [18]. In some conditions long-term (24-h) recordings have been more sensitive in detecting abnormalities in autonomic function than short-term variables [18], but this technique might
Conclusions
This study reports normal ranges of HRV indices and demonstrates that the modification of HRV is partially age- and gender-dependent, and varies with the different HRV variables. This modification may reflect an evolution of the autonomic nervous system with growth. These data will enable us to compare HRV in pediatric populations by dividing for gender- and age-class for SDNN and SDANN, and only for age class (<5 years versus >5 years of age) for SDNN-i, pNN50 and rMSSD.
Acknowledgements
We thank G. Grutter, V. Di Ciommo and L. Ravà, Epidemiology Unit, Bambino Gesù Hospital, for their help with the statistical analysis.
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Preliminary data of this study were presented at Progress in Clinical Pacing, VIII International Symposium, Rome 1–4/12/98.