Thyroid gland dysfunction and its effect on the cardiovascular system: a comprehensive review of the literature

There is an intimate and functional relationship between the cardiovascular system and the thyroid gland; from sharing the same embryologic origin to modulating each of the components of the heart for a normal function. Due to this relationship, patients suffering from cardiovascular diseases often undergo a thyroid function test to rule out hypo- or hyperthyroidism. The signs and symptoms of hyper- and hypothyroidism are clinically relevant and profound. The cardiac function changes can be explained through the cellular mechanism of the thyroid hormone action on the heart. Minor alteration of thyroid hormone can change vascular resistance, cardiac contractility, blood pressure, and heart rhythm, because of the presence of the thyroid hormone receptors on these tissues. A better understanding of the impact of thyroid hormones on the cardiovascular system is paramount for physicians to make a quick decision and initiate a treatment plan because it has been shown to reverse some of the cardiac changes such as systolic and diastolic dysfunction. With this literature review, we aim to describe the holistic effect of thyroid hormones on the cardiovascular system, from its effect on a cellular level to changes in cardiac functions in subclinical and overt hypo/hyperthyroidism. Additionally, we will describe the effects of the drug treatment regimen of thyroid on the cardiac function.