The Role of Thyroid Hormone in Heart Disease

Abstract

Thyroid hormone can have an impact on several molecular pathways in both the circulatory system and the heart, either by increasing or decreasing their activity. This can result in the emergence of pertinent cardiovascular diseases. It is widely acknowledged that overt hyperthyroidism can result in a hyperdynamic cardiovascular condition, defined by excessive cardiac output and low systemic vascular resistance. In contrast, overt hypothyroidism is associated with the opposite changes, including an accelerated heart rate, improved function of the left ventricle (LV) during both systole and diastole, and a higher occurrence of supraventricular tachyarrhythmias, such as atrial fibrillation. These modifications are linked to an increased likelihood of developing congestive heart failure. Nevertheless, it remains uncertain whether variations in cardiac function related to evident thyroid disorders are primarily attributable to changes in cardiac workload or irregularities in myocardial contractility. There is a significant amount of research that shows the cardiovascular system responds to the small yet consistent fluctuations in thyroid hormone levels in the bloodstream. These alterations suggest that individuals have subclinical thyroid impairment. Subclinical hyperthyroidism is linked to various negative health consequences,

 such as an elevated risk of cardiovascular mortality, an elevated heart rate, atrial arrhythmias, left ventricular hypertrophy, and reduced exercise capacity. Subclinical hypothyroidism is not only linked to a moderate level of dysfunction in the left ventricle's systolic and diastolic functions, but it also increases the likelihood of developing atherosclerosis and experiencing a myocardial infarction. Given that all cardiovascular abnormalities can be reversed by restoring euthyroidism (also referred to as "subclinical hypothyroidism") or reduced by -blockade and L-thyroxine (L-T4) dose adjustment (also known as "subclinical hyperthyroidism"), it is advisable to promptly initiate treatment to prevent any negative impact on the cardiovascular system. It is noteworthy that certain research indicates that patients who have had cardiac surgery, as well as those with acute and chronic cardiovascular issues, may experience changes in the metabolism of peripheral thyroid hormone, potentially impacting heart function. Initial clinical data indicate that individuals suffering from acute and chronic cardiovascular illness may experience substantial advantages from the administration of thyroid hormone or its analogue, 3,5-diiodothyropionic acid. This holds true irrespective of whether the patients are suffering from acute or chronic cardiovascular disease. Considering this information, it seems that administering thyroid hormone might be advantageous in the treatment of these patients.

Keywords: hyperthyroidism, hyperdynamic cardiovascular condition, thyroid disorders, irregularities in myocardial contractility.