One of the most common diseases of the cardiovascular system is cardiac arrhythmias. Assessment of the heart rate is one of the obligatory methods of pediatric examination and its deviation from the age norm may indicate a change in the child's health and be one of the first manifestations of the disease. Heart rhythm disturbances accompany various diseases, namely: congenital heart defects, cardiomyopathies, rheumatic and infectious diseases, intoxication, vegetative crises, endocrine diseases, diseases of the nervous system and others. Most often, in children's practice, it is not always possible to establish the cause of heart rhythm disturbances, as well as to classify the presence of organic or functional disorders without conducting morphological studies. Purpose — to study the features of heart rhythm and the state of the autonomic nervous system (ANS) among the children of primary school age with sinus bradycardia. Materials and methods. Children of primary school age with sinus bradycardia were examined (210 children). All children underwent: clinical examination, ECG at rest and after exercise, daily monitoring of ECG and heart rate, echocardiography, cardiointervalography with spectral analysis of heart rate. Results. Assessment of the cardiovascular system among children with bradycardia revealed the following features: 80.0% of children had no complaints, 68.0% of children at the age of 6–7 years and 55.0% of children at the age of 8–10 years had moderate bradycardia, 32.0% of children at the age of 6–7 years and 45.0% of children at the age of 8–10 years had significant bradycardia. After the exercise test, 71.0% of children still had bradycardia, which is typical for children at the age of 9–10 years and 29.0% of children had an acceleration of heart rate above the age norm. Holter monitoring revealed the following cardiac arrhythmias: sinus rhythm driver migration, ectopic rhythm, sinoatrial block, 2 grade atrioventricular block, atrial extrasystole and ventricular extrasystole. Different duration of sinoatrial pauses was detected: in the range from 1300–1400 ms among the most children (78.0%) to 1700–1800 ms among 1.8% of children. Data from spectral analysis of sinus rhythm showed the predominance of parasympathetic nervous system tone among the 84.0% of children, asympathicotonic (40.5%) and normal (44.9%) autonomic reactivity. Conclusions. Examination of the children of the primary school age revealed sinus bradycardia and bradyarrhythmia among the 80.7% of children. Bradyarrhythmia is typical for children at the age of 6–7 years, bradycardia — for children at the age of 9–10 years. Spectral analysis of the ANS showed an imbalance in the regulation of sinus rhythm: the predominance of the parasympathetic link, regardless of the initial state of the ANS and the violation of adaptive mechanisms. According to Holter monitoring, the duration of pauses is longer than normal for the given age (more than 1300 ms) indicates sinus node dysfunction and requires closer monitoring due to the risk of developing sinus node weakness syndrome and other threatening conditions in later life. The research was carried out in accordance with the principles of the Helsinki declaration. The study protocol was approved by the Local ethics committee of all participating institution. The informed consent of the patient was obtained for conducting the studies. No conflict of interest was declared by the authors. Key words: children, bradycardia, bradyarrhythmia, vegetative homeostasis.
