Impact of hormone replacement therapy on cardiovascular risk in patients with hypothyroidism: a systematic review

Abstract

Hypothyroidism, which is developed in 4-10 % of the population, and subclinical hypothyroidism found in more than 10 % of people which are highly associated with cardiovascular pathophysiology at some level. Hypothyroidism, which is the most frequent endocrine disorder with a lack of enough thyroid hormones, presents a wide range of cardiovascular complications, including coronary artery disease, heart failure, and dyslipidemia. Thyroid hormone replacement therapy, particularly levothyroxine (LT4), continues to be the central management of hypothyroidism, which aims to restore euthyroidism and other cardiac comorbidities as well as relieving symptoms. Nonetheless, the complex interworking of thyroid function and cardiovascular health requires a detailed clarification of the processes associated with disease development and drug therapy. Hypothyroidism triggers a chain of cardiovascular alterations such as aberrant lipid metabolism, endothelial dysfunction, and lessened cardiac contractility primarily by lowering the thyroid hormone level. Besides, these modifications eventually lead to raised rates of atherosclerosis, myocardial infarction, and heart failure. LT4 replacement therapy achieves normalization of hyperthyroidism with the replacement of thyroid hormone deficiency, which restores the cardiovascular system to normal by doing so. LT4 modulates lipid metabolism, improves endothelial function, and stimulates myocardial contractility via several different mechanisms. LT4 therapy acts on systemic inflammation and oxidation to accentuate the protective effects of the cardiovascular system. Apart from this, there is an increasing awareness about the use of new thyroid hormone formulations, like LH4, in the therapy of hypothyroidism. LH4, the thyromimetic compound, demonstrated a similar binding affinity at the thyroid hormone receptor as T3 (triiodothyronine) but with better tissue selectivity and more metabolic stability. Clinical trials have proven the potency of LH4 in lowering symptoms of hypothyroidism, for example, fatigue, weight gain which are leading cause of cardiovascular disorders. LH4 administration has been safe for up to six months, and only mild adverse effects have been reported when it is used more than a year.