Alterations of heart rate variability and turbulence in female patients with hyperthyroidism of various severities

OBJECTIVE: The objective of the this study is to document the existence of statistically significant differences between parameters of heart rate variability (HRV) and heart rate turbulence (HRT), determined in women with overt hyperthyroidism (hT), compared to controls and to highlight their correlations with the level of thyroid hormones and the incidence of arrhythmias. METHODS: We studied the HRV in time and frequency domain, and the HRT in a group of 113 women with overt hT, without other cardiovascular risk factors or comorbidities, admitted to the endocrinology clinic of our hospital, between 2012 and 2016. Depending on the severity and duration of hT and levels of thyroid hormones, the patients were assigned to three groups: mild and moderate forms, severe hT with thyrotoxicosis and persistent cases with a relapse of hT. We performed 24 h Holter monitoring in all patients. RESULTS: HRV parameters in time domain (TD) were significantly depressed in patients comparing to controls. All patients had abnormal, positive values of turbulence onset (TO) with significant statistically differences (P < 0.0001) comparing to controls. Although positive, the values of turbulence slope (TS) decreased according to the severity of hT. CONCLUSION: Patients with hT had depressed values of HRV parameters in TD, correlated with the severity of the thyroid disease and with the incidence of arrhythmias. All patients presented pathological values of TO. TS values were positive, but lower compared to controls.