[Cardiovascular manifestations of thyrotoxicosis and thyroid dysfunction caused by amiodarone]

Abstract

Cardiovascular manifestations of thyrotoxicosis and thyroid dysfunction caused by amiodarone. The cardiovascular symptoms of thyrotoxicosis were described more than two hundred years ago and remained the basis of diagnosis in modern medicine. Myocardium, peripheral circulation and sympathetic nerve system, all affecting cardiovascular hemodynamics, are influenced by thyroid hormones in many ways. Sub-clinical hyperthyroidism is characterized by suppressed thyroid stimulating hormone and normal free triiodothyronine and free thyroxine levels. Cardiovascular symptoms: elevation of heart rate, myocardial contractility, stroke volume, myocardial oxygen consumption, systolic blood pressure and reduction in systemic vascular resistance and diastolic blood pressure can be often seen even in case of subclinical hyperthyroidism. Thyrotoxicosis exacerbates the symptoms of a preexisting heart disease, but it can also cause complaints in case of a structurally normal heart. The most common cardiac complications are arrhythmias (mainly atrial fibrillation), heart failure and hypertension. Amiodarone is used for the treatment and prevention of several arrhythmias. It is safely applicable even in case of left ventricular dysfunction. The more common application is limited by its side effects that can develop even at low doses and may involve several organs (thyroid gland, lungs, liver, heart, nerve system among others). The complex effect of amiodarone on thyroid function ranges from mild abnormalities of thyroid function tests to overt thyrotoxicosis or hypothyroidism.