Mechanisms of Autonomic Dysfunction in Hypothyroidism and Associated Cardiovascular Outcomes

Hypothyroidism is strongly linked with alterations in autonomic nervous system (ANS) control of the cardiovascular system, reflected in changes in heart rate variability (HRV), baroreflex sensitivity, vascular tone and electrophysiological stability. These autonomic changes contribute to an increased risk of hypertension, atherosclerosis, heart failure and arrhythmias, even in subclinical disease. Thyroid hormones act at multiple levels of the central and peripheral autonomic network, including the central autonomic nuclei, baroreflex pathways, vascular endothelium, myocardium and metabolic–inflammatory milieu. In overt hypothyroidism, the typical pattern is reduced sympathetic and parasympathetic cardiac modulation with impaired baroreflex function and increased systemic vascular resistance. Subclinical hypothyroidism shows similar but milder disturbances. Growing evidence indicates that a portion of the excess cardiovascular risk in hypothyroidism is mediated through autonomic dysregulation. This narrative review summarises current knowledge on the mechanisms linking thyroid hormone deficiency to autonomic dysfunction and synthesises clinical evidence relating these mechanisms to cardiovascular outcomes. It also highlights the reversibility of some autonomic abnormalities with levothyroxine therapy and proposes directions for future research, including standardized autonomic testing protocols and the use of HRV and baroreflex indices as prognostic tools in hypothyroid populations