Cardiac Autonomic Regulation Is Disturbed in Children with Euthyroid Hashimoto Thyroiditis

Evaluation of heart rate variability, QT dispersion, and Tp-e interval in pediatric subclinical hypothyroidism

BACKGROUND

Clinical effects of subclinical hypothyroidism are not clearly understood. This study aims to investigate the effects of subclinical hypothyroidism (SH) on cardiac autonomic and conduction systems in children.

METHODS

Forty-seven cases (25 female, 22 male) with SH aged between 3 and 17 years and 46 controls that were age, body mass index and sex matched, were included in the study. Heart rate variability (HRV) was used to evaluate cardiac autonomic function while QT dispersion, P dispersion and Tp-e measurements from ECGs to evaluate susceptibility to arrhythmia.

RESULTS

Standard deviation of the average of Normal-Normal intervals in 5-minute measurements was lower in the SH group compared to controls. No statistically significant differences were found in other time or frequency domain parameters. Maximum and minimum corrected QT intervals were longer in the SH group (p = 0.047 and p = 0.012, respectively); there were no significant differences in other ECG parameters.

CONCLUSION

Our study demonstrates that cardiac autonomic dysfunction and arrhyhtmogenesis shown as susceptibility to ventricular arrhythmia and longer intraatrial conduction times, appear in children with SH.

IMPACT

To our knowledge, this is the first study to show changes in cardiac autonomic function using heart rate variability in children with subclinical hypothyroidism (SH). We suppose that the fact that ventricular repolarization is longer in children with SH regardless of heart rate shows a predisposition to ventricular arrhythmia. Our study demonstrates that cardiac autonomic dysfunction and arrhythmogenesis shown as susceptibility to ventricular arrhythmia and longer intraatrial conduction times, appear in children with SH. We suggest that an evaluation regarding arrhythymia together with endocrinological follow-up is warranted when children are diagnosed with SH.

Assessing heart rate variability in type 1 diabetes mellitus-Psychosocial stress a possible confounder

BACKGROUND

Autonomic neuropathy (AN) commonly arises as a long-term complication in diabetes mellitus and can be diagnosed from heart rate variability (HRV), calculated from electrocardiogram recordings. Psychosocial stress also affects HRV and could be one of several confounders for cardiac AN. The present work investigated the impact of psychosocial stress on HRV in individuals with type 1 diabetes mellitus (T1DM) and assessed the use of salivary cortisol as a biomarker for psychosocial stress in this context.

METHODS

A total of 167 individuals 6-60 years old (113 with T1DM and 54 healthy controls) underwent 24-hr ECG recordings with HRV analysis. Salivary cortisol was sampled thrice during the registration day. Perceived psychosocial stress along with other factors of possible importance for the interpretation of HRV was documented in a diary.

RESULTS

Heart rate variability (high-frequency power during sleep) was reduced (p < .05) with older age, longer diabetes duration, higher mean glucose levels, physical inactivity, and perceived psychosocial stress. Salivary cortisol levels in the evening were increased (p < .05) in women in ovulation phase, in individuals with preceding hypoglycemia or with hyperglycemia. The amplitude of salivary cortisol was reduced (p < .05) with the presence of perceived psychosocial stress, but only in adult healthy controls, not in individuals with diabetes.

CONCLUSION

Psychosocial stress might be a confounder for reduced HRV when diagnosing cardiac AN in T1DM. Salivary cortisol is, however, not a useful biomarker for psychosocial stress in diabetes since the physiological stress of both hypoglycemia and hyperglycemia seems to overrule the effect of psychosocial stress on cortisol.

Evaluation of cardiac autonomic function using heart rate variability in children with acute carbon monoxide poisoning

Introduction Carbon monoxide poisoning may cause myocardial toxicity and cardiac autonomic dysfunction, which may contribute to the development of life-threatening arrhythmias. We investigated the potential association between acute carbon monoxide exposure and cardiac autonomic function measured by heart rate variability.

METHOD

The present study included 40 children aged 1-17 years who were admitted to the Pediatric Intensive Care Unit with acute carbon monoxide poisoning and 40 healthy age- and sex-matched controls. Carboxyhaemoglobin and cardiac enzymes were measured at admission. Electrocardiography was performed on admission and discharge, and 24-hour Holter electrocardiography was digitally recorded. Heart rate variability was analysed at both time points - 24-hour recordings - and frequency domains - from the first 5 minutes of intensive care unit admission.

RESULTS

Time domain and frequency indices such as high-frequency spectral power and low-frequency spectral power were similar between patient and control groups (p>0.05). The ratio of low-frequency spectral power to high-frequency spectral power was significantly lower in the carbon monoxide poisoning group (p<0.001) and was negatively correlated with carboxyhaemoglobin levels (r=-0.351, p<0.05). The mean heart rate, QT dispersion, corrected QT dispersion, and P dispersion values were higher in the carbon monoxide poisoning group (p<0.05) on admission. The QT dispersion and corrected QT dispersion remained longer in the carbon monoxide poisoning group compared with controls on discharge (p<0.05).

CONCLUSION

The frequency domain indices, especially the ratio of low-frequency spectral power to high-frequency spectral power, are useful for the evaluation of the cardiac autonomic function. The decreased low-frequency spectral power-to-high-frequency spectral power ratio reflects a balance of the autonomic nervous system, which shifted to parasympathetic components.