Effects of levothyroxine therapy on cardiac functions in patients with compensated hypothyroidism

It has been long known that thyroid diseases have effects on cardiovascular system. Thyroid hormones have positive chronotropic effects. As in preload, the afterload is also effective in the determination of end-diastolic volume and myocardial performance. The afterload is the major determinant of the stroke volume. It is regulated by arterial pressure in normal organism. The changes in ventricular size and geometry can also affect afterload. Thyroid hormones reduce systemic vascular resistance in acute and chronic manner by directly causing relaxation of arterial smooth muscles. The compensated hypothyroidism can cause disruption in myocardium, diastolic dysfunction, abnormal myocardial conformation in the video densitometry analysis, and reduced maximal aortic flow rate, cardiac index, vital capacity and oxygen uptake during exercise. A marked improvement in cardiac functions was detected in this group of patients in the studies comparing cardiac functions before and after treatment with levothyroxine in adult patients. However, there is limited number of studies on this topic in pediatric population. Thus, we conducted this study to assess cardiac functions in this group of patients and to demonstrate effects of levothyroxine treatment on cardiac functions in these patients. The study included 31 patients presented to Pediatric Endocrinology Department of Akdeniz University, Medicine School with elevated TSH levels and 20 healthy infant with similar age and BMI as control group. The patients assigned into four groups as follows: the patients diagnosed as compensated hypothyroidism receiving therapy; the patients diagnosed as compensated hypothyroidism receiving no therapy; the patients diagnosed as decompensated hypothyroidism; and controls. Among these groups, EF, FS, IVS, LVIDd and LIVDs values were compared by using PWD regarding systolic functions, while E, A, E/A values were compared by using PWDD regarding diastolic functions. In addition, E?, A?, E?/A? values and cardiac intervals including IVCT, IVRT, DT, ET and MPI values were compared by using PWDD. In conclusion, the lack of improvement after 3-months follow-up in the cardiac parameters which were initially found to be significantly different in the patients diagnosed as compensated hypothyroidism receiving no therapy when compared to healthy controls, the observation of improvement in diastolic functions after 3-months of therapy in patients with compensated hypothyroidism receiving therapy, the finding that systolic and diastolic functions were found to be better in patients with compensated hypothyroidism receiving therapy when compared to those not receiving therapy, the recovery of initial changes after 3-months levothyroxine therapy which could be interpreted as systolic and diastolic dysfunction in decompensated hypothyroidism group with more severe hypothyroidism compared to other patient groups indicate the presence of cardiac involvement with varying severity in cases at the various points of hypothyroidism spectrum and healing effects of LT4 therapy on cardiac parameters. There is a need for prospective, randomized, controlled studies in this field