Spectral analysis of heart rate variability in persons with mild subclinical hypothyroidism

Overview

Spectral analysis of heart rate variability (HRV) is a non-invasive method suitable for clinical practice but not yet widely used. It allows the sympathetic – parasympathetic modulation of the heart rate to be monitored. The aim of the study was to investigate whether the HRV in patients with subclinical hypothyroidism is disturbed in the same way as in patients with manifest hypothyroidism. In has been demonstrated that patients with manifest hypothyroidism show decreased total HRV and a decrease in the parasympathetic influence both when lying down and standing up, and their relative and absolute sympathetic tonus is also increased. All these parameters become normal once normal thyroid function is achieved.

Twenty three females with subclinical hypothyroidism (TSH 4, 5–10 mU/l) were examined, 83 % of them had chronic autoimmune thyroiditis. As controls we used 23 healthy females with no history of thyroid disease. When the patients lay down we noted lowered total spectral effort and lowered low frequency components which correspond with the sympathetic influence. No significant differences in HRV compared with healthy controls were found when the patients were standing up.

Key words:
autonomic regulation, subclinical hypothyroidism, heart rate variability (HRV).