Evaluation of Autonomic Functions for Assessment of Cardiovascular Risk in Women with Subclinical Hypothyroidism

Objectives: The objective is to evaluate the autonomic function tests to assess cardiovascular risk in women with subclinical hypothyroidism (SH). Materials and Methods: Women aged 20–55 years attending the All India Institute of Medical Sciences outpatient department with SH were recruited for the study. Women with euthyroid state were taken as controls (age-matched). The subjects are assigned into 2 groups based on clinical features and laboratory investigations: Group I: 58 women with SH, Group II: 50 healthy women with euthyroid state (controls). Resting electrocardiography (ECG) recording was obtained for 5 min for generating R-R interval series from selected lead II for measurement of heart rate variability (HRV), and the bedside battery of tests for autonomic reactivity was performed. Results: HRV indices measured from 5-min ECG recordings showed a decrease in HRV parameters in Group I females compared to the control group, reflecting lower autonomic nervous system activity. 47% ( n = 27) of females with SH had abnormal sympathetic autonomic tests. 29% ( n = 17) of females with SH had abnormal heart rate response to deep breathing and standing, considered as parasympathetic dysfunction. Conclusion: Our study revealed that women with SH had decreased HRV with reduced sympatho-vagal tone and autonomic reactivity. Sympathetic dysfunction was predominant in SH, although parasympathetic dysfunction was also seen.