Heart Rate Turbulence Analysis in Subclinical Hypothroidism Heart Rate Turbulence in Hypothyroidism.

Background: Heart rate turbulence (HRT) is a baroreflex-mediated biphasic reaction of heart rate in response to premature ventricular beats. Abnormal HRT identifies patients with autonomic dysfunction or impaired baroreflex sensitivity. The aim of the present study was to demonstrate the effect of subclinical hypothyroidism (SCH) on cardiac autonomic function using HRT parameters.

Methods: The study sample consisted of 25 patients (10 men, 15 women with a mean age of 39.7 ± 15.5 years) who were diagnosed with SCH and 35 euthyroid patients (13 males, 22 females with a mean age 38.4 ± 11.7 years). All patients underwent 24 h ambulatory electrocardiography monitorization. The study calculated two HRT parameters, turbulence slope (TS) and turbulence onset (TO), and these HRT parameters were compared between the groups to examine the relationship between HRT and thyroid-stimulating hormone (TSH) levels.

Results: The characteristics of SCH patients and control cases were similar with regard to age, sex except for TSH levels. Serum TSH levels were significantly higher in SCH patients than in the controls (7.3 ± 1.8 μIU/ml vs. 2.4 ± 1.0 μIU/ml, p < 0.001). TO was significantly higher in SCH patients compared with controls (-1.51 ± 0.5 vs. -2.2 ± 1.0, p = 0.002). SCH patients had lower TS values than controls (7.6 ± 2.4 vs. 10.8 ± 3.4, p < 0.001). TO was positively correlated with serum TSH levels (r = 0.276, p = 0.033). There was also a negative correlation between TS and serum TSH levels (r = -0.437, p < 0.001).

Conclusions: The results of our study indicated that cardiac autonomic function is impaired in patients with SCH.

Key Words: Heart rate; Holter electrocardiography; Hypothyroidism.