Effect of Hypothyroidism in Cardiovascular System

Effect of Hypothyroidism in Cardiovascular System
Seyyed Hossein Heidari ,¹ Mehrdad Ostadpoor ,² Nasser Yazdani ,^3,*
1. Doctor of Veterinary Medicine, Islamic Azad University, Shahrekord Branch, Shahrekord, Iran
2. Doctor of Veterinary Medicine, Islamic Azad University, Shahrekord Branch, Shahrekord, Iran
3. Doctor of Veterinary Medicine, Islamic Azad University, Shahrekord Branch, Shahrekord, Iran
Introduction: Hypothyroidism is defined as an elevated serum level of thyroid stimulating hormone (TSH), with free thyroxine (FT4) or triiodothyronine (FT3) levels within or below the reference range common in the general population. Increasing number of studies have indicated that thyroid hormones may play an important role in the maintenance of cardiovascular homeostasis under physiologic and pathologic conditions. It is also involved in modulating cardiac contractility, heart rate, diastolic function, and systemic vascular resistance, thereby affecting cardiac function. Thyroid dysfunction is a risk factor of cardiovascular disease.
Methods: In the current study, key words including hypothyroidism, thyroid-stimulating hormone, thyroxine and cardiovascular disease were reviewed from the list of Mesh and other credible websites including PubMed, Science Direct and Google Scholar over the past two decades and the desired data was organized.
Results: Thyroid hormones have a variety of effects on the cardiovascular system that can greatly impact cardiac function. Hypothyroidism is associated with decreased cardiac output due to the impaired relaxation of vascular smooth muscle and decreased availability of endothelial nitric oxide. This produces a cascade effect of increased arterial stiffness that leads to increased systemic vascular resistance. On a molecular level, these alterations result from the reduced expression of sarcoplasmic reticulum Ca2+-ATPase and increased expression of phospholamban, which inhibits ATPase. Thyroid hormones also impact the renin-angiotensin-aldosterone system. Hypothyroidism decreases cardiac output, increases systemic vascular resistance, decreases arterial compliance, narrows pulse pressure, increases diastolic pressure, atherosclerosis, increases risk of coronary artery disease, decreases nitric oxide production, decreases vascular smooth muscle relaxation, decreases cardiac contractility and decreases vascular smooth muscle relaxation.
Conclusion: It is clear that thyroid hormones play a significant role in regulating cardiac, vascular, and metabolic physiology. Physiologic alterations from both overt and subclinical hypothyroidism have varied cardiovascular effects and treatment may reverse some, if not all, of the effects. There is evidence to suggest that treatment of mild dysfunction can improve cardiovascular outcomes.
Keywords: Hypothyroidism, cardiovascular disease, thyroxine, thyroid-stimulating hormone