Objective. To evaluate the results of 72-hour monitoring of Holter electrocardiograms with telemetry in children with hypertrophic cardiomyopathy (HCM). Patients and methods. A randomized retrospective study of 55 children with the confirmed diagnosis of HCM was conducted on the basis of the Federal State Autonomous Institution of the Ministry of Health of Russian Federation "National Children Medical Research Center"; all patients were hospitalized in the cardiology department for the examination and treatment in the period 2021–2023. The study included 33 boys and 22 girls aged 6 to 17.8 years; age and documented functional limitations in both groups were comparable. All patients underwent electrocardiography (ECG) on the 12-channel electrocardiograph; 3-channel 3-day monitoring of Holter electrocardiograms with telemetry using the Astrocard-Telemetry 3G complex (Meditek, Russia); magnetic resonance imaging (MRI) of the heart with intravenous contrast. Parents of 43 patients filled out questionnaires identifying direct and indirect signs of sleep disorders. The obtained data were presented in fractions, as well as as M ± m; minimum, Q1, Q3, maximum; and the Kendall rank correlation coefficient and the Friedman criterion were calculated daily. The differences were considered significant at p < 0.05. The work has been approved by an independent local ethics committee. All parents (or legal representatives) of the children signed the voluntary informed Results. 12-channel ECG revealed various and non-specific disorders (arrhythmias, signs of overload of the heart chambers) in 50 (90.9%) patients. Long-term (3-day) Holter monitoring revealed practically no significant differences in the mean values of the studied indicators between days; by the 3rd day of the study, two trends were revealed: an increase in the average number of episodes of ventricular tachycardia (p = 0.058) and an elongation of the QTc interval in boys (p = 0.053). The significant decrease in heart rate was recorded in girls on the 3rd day of the study (p = 0.011). According to the results of MRI, intramyocardial fibrosis was detected in 37 (67.3%) cases: in 23 (69.7%) boys and 14 (63.6%) girls. In 16 (29.1%) patients, the volume of myocardial lesion was ≥10%. Direct and/or indirect signs of respiratory disorders during sleep were recorded in 28 (65.1%) children. In children with signs of sleep disorders, significant positive correlations were found with the number of supraventricular and ventricular extrasystoles and episodes of ventricular tachycardia. Signs of an increased risk of sudden vascular death were recorded in 8 (14.5%) children. Conclusion. Long-term (3-day) Holter monitoring of electrocardiograms is well adapted to children; all major rhythm disturbances were detected during the first 24 hours. Prolongation of the study may be recommended to solve certain clinical problems (diagnosis of syncopal conditions, paroxysms of unclear etiology, sleep apnea). In children with HCM, it is necessary to identify direct and indirect signs of sleep disorders that have significant correlations with cardiac arrhythmias, including those that are an integrative indicator of the risk of sudden cardiac death. Key words: sudden cardiac death, hypertrophic cardiomyopathy, children, multi-day monitoring of electrocardiogram with telemetry, rhythm disturbances, sleep disorders

Objective. To analyze clinical and instrumental characteristics of sleep disorders in children with cardiomyopathies (CMPs). Patients and methods. We performed retrospective analysis of clinical, laboratory, and instrumental parameters in 107 children with CMPs aged 2 to 17 years treated in the National Medical Research Center of Children's Health in 2018–2019. The study sample was formed in accordance with inclusion criteria (confirmed diagnosis of CMP with functional class I or II, NYHA or Ross R.D.) and exclusion criteria (age <2 years, other heart and vascular diseases). We enrolled 26 children with hypertrophic CMP, 63 children with dilated CMP, and 18 children with unclassified CMP. According to the signs of sleep disorders (from sleep questionnaires filled in by parents), we formed 3 groups: patients with no sleep disorders (n = 40), patients with symptoms of insomnia/parasomnia (n = 26), and patients with indirect and/or direct signs of sleep apnea syndrome (SAS). We analyzed patients’ complaints, as well as clinical, instrumental (liver ultrasound, echocardiography, Holter ECG), and laboratory (glucose, cholesterol, alanine aminotransferase, and aspartate aminotransferase in serum) parameters. Results. Sleep disorders were identified in 63% of children: 58% had signs of insomnia/parasomnia and 38% had signs of SAS. In contrast to the questionnaires, medical records had information about sleep disorders only in two cases. Medical records primarily contained complaints of fatigue and reduced tolerance to physical activity (73%), excessive sweating (23%), and shortness of breath (17%). Patients with SAS usually had more complaints (according to their medical records), and their complaints were more diverse, including abnormal blood pressure, cephalgia, palpitations, and syncope. Body mass index (BMI) (p = 0.001) and serum glucose (p = 0.001) were higher in children with SAS than in children with normal sleep. Even after the exclusion of BMI, glucose levels (although being within the reference range) were still significantly higher in the SAS group (p = 0.020). The QTc interval at the maximum heart rate (HR) (p = 0.018) in children with sleep disorders was longer and had a positive correlation with serum glucose level (r = 0.195, p = 0.052). The analysis of echocardiography parameters (excluding the diagnosis factor) showed a smaller diameter of the pulmonary artery (p = 0.058) in children with SAS and correlation between right atrial remodeling and the factor of sleep disorder in children with various forms of CMP (p = 0.040). Conclusion. The analysis of sleep questionnaires revealed sleep disorders in 63% of children with CMP, including insomnia/parasomnia (24%) and/or SAS (38%). The presence of SAS was associated with a substantial number and variety of subjective complaints. The signs of myocardial electrical instability (longer QTc interval at maximum heart rate), association between QTc and serum glucose level, specific features of remodeling of the heart and blood vessels in patients with sleep disorders, and, most importantly, SAS in children indicate the need for early detection and correction of sleep disorders (insomnia, parasomnia) and main causes of SAS, such as chronic diseases of the ENT organs, overweight, and obesity. Treatment of sleep disorders is very important in terms of prevention of complications, treatment and prognosis of cardiomyopathy in children, which will help to increase therapeutic efficacy. Key words: children, cardiomyopathy, comorbidity, sleep disorders, sleep apnea, sleep questionnaires