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ORIGINAL ARTICLE
Year : 2016  |  Volume : 20  |  Issue : 5  |  Page : 605-611

Cardiac autonomic function and vascular profile in subclinical hypothyroidism: Increased beat-to-beat QT variability


1 Department of Endocrinology, M.S. Ramaiah Medical College, Bengaluru, Karnataka, India
2 Department of Psychiatry, University of Alberta, Edmonton, Alberta, Canada
3 Centre for Diabetes and Endocrine Care, Bangalore Diabetes Hospital, Bengaluru, Karnataka, India

Correspondence Address:
Pramila Kalra
Department of Endocrinology, M.S. Ramaiah Medical College, Bengaluru - 560 054, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2230-8210.190527

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Background: Patients with subclinical hypothyroidism (SH) may have higher incidence of coronary heart disease and autonomic dysfunction. Design of the Study: Prospective case control study. Aim and Objectives: To evaluate beat-to-beat QT variability and vascular stiffness in patients with SH compared to normal controls. Materials and Methods: We compared linear and nonlinear measures of cardiac repolarization liability using beat-to-beat QT intervals derived from the surface electrocardiogram during supine posture and vascular indices including pulse wave velocity and ankle-brachial index (ABI) during supine posture between female patients with SH and age- and sex-matched normal controls. Spectral analysis was done at very low frequency (LF) (0.003-0.04 Hz), Low frequency (LF) (0.04-0.15 Hz), and high frequency (HF) (0.15-0.4 Hz). The HF represents vagal regulation (parasympathetic) and LF represents both parasympathetic and sympathetic regulation. Results: We recruited 58 women with a mean age of 31.83 ± 8.9 years and 49 controls with mean age of 32.4 ± 9.9 years (P = NS). QT variability index (QTvi) was higher in cases compared to controls (P = 0.01). The ratio of LF/HF of R-R interval which is an index of sympathovagal tone was significantly more in cases compared to controls (P = 0.02). The difference in the left minus the right ABI was significant between cases and controls (P = 0.03). Conclusions: The cases had lower parasympathetic activity as compared to controls, and there was a predominance of sympathetic activity in cases. QTvi may be an important noninvasive tool in this group of patients to study the risk of cardiovascular mortality.


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