Background Hypothyroidism increases the risk of cardiac disease as well as autonomic dysfunction (abnormalities of the autonomic nervous system). A prospective case-control study was conducted. The purpose of this study was to compare the QT variability and vascular stiffness of SH patients.

Materials and Methods:Using ABI, we compared female SH patients to age- and sex-matched normal controls in order to better understand their condition. HF (0.15–0.4 Hz) and LF (0.003–0.04 Hz) frequencies were investigated spectroscopically. The HF represents vagal regulation, whereas the LF reflects both vagal and limbic regulation.

Result In this case research 32 women participated  who were 28.02+7.8 years old and 28 women in control group who were age-matched (30.2+ 7.1). Patients had greater QT variability indices (P = 0.01) than healthy controls. Cases showed a higher LF/HF ratio than controls (P = 0.03), which was statistically significant. It was shown that there was a 0.02 point difference in left-right ABI between patients and controls.

Conclusion In these circumstances, sympathetic activity predominated over parasympathetic activity, with less of the latter. QTvi may be beneficial in determining the risk of cardiovascular mortality in this particular patient population.