Dyslipidemia and low-grade inflammation are associated with sympathovagal imbalance and cardiovascular risks in subclinical and overt hypothyroidism

Background and Aim: Hypothyroidism in both its subclinical and overt form has been reported to be associated with cardiovascular (CV) morbidities. Dyslipidemia, inflammation, and sympathovagal imbalance (SVI) contribute to CV risks. The present study has assessed role of dyslipidemia and inflammation in the genesis of SVI and hypertension status in subclinical hypothyroidism (SCH) and overt hypothyroidism (OH). Methods: Age-matched 209 females (70 euthyroids, 67 subclinical hypothyroids, and 72 overt hypothyroids) were recruited for this study. Body mass index (BMI), CV parameters, and autonomic function tests (AFT) like spectral analysis of heart rate variability (HRV), heart rate (HR) response to standing, HR response to deep breathing, and blood pressure (BP) response to isometric handgrip were assessed. Thyroid profile, lipid profile, and immunological and inflammatory markers were estimated. The independent association of the ratio of low-frequency to high-frequency (LF-HF ratio) power of HRV and the marker of SVI with various parameters were determined by multiple regression analysis. The prediction of hypertension status by LF-HF ratio was assessed by logistic regression. Results: CV and AFT parameters, lipid profile, and inflammatory marker were altered and correlated with LF-HF ratio in both SCH and OH groups. Mean arterial pressure, atherogenic index, and high-sensitive C-reactive protein had independent contribution to LF-HF ratio in both the groups. The prediction of hypertension status by LF-HF ratio was more significant in OH groups (odds ratio (OR) 2.15, CI 0.126-5.867, and P = 0.002) compared to SCH group (OR 1.90, CI 1.108-4.352, and P = 0.009). Conclusion: SVI due to sympathetic activation and vagal withdrawal occurs in SCH that progressively increases from SCH to OH. Dyslipidemia and low-grade inflammation are associated with SVI and CV risks in hypothyroidism.