Abstract.
Non-thyroidal illness syndrome (NTIS) also known as euthyroid sick syndrome or low T3 syndrome is hypothyroidism caused by peripheral changes in the metabolism and thyroid hormone transport caused by severe debilitating diseases, in particular, heart failure. Recent data indicate that chronic heart failure can result in thyroid hormone metabolism disruption, which contributes to a progressive decrease in the concentration of triiodothyronine. The objective was to evaluate the effectiveness and safety of hormone replacement therapy with low doses of thyroxine in congestive heart failure in patients with low triiodothyronine syndrome. The levels of thyroid-stimulating hormone, thyroxine-binding globulin, free thyroxine, total triiodothyronine, free triiodothyronine, and reversible triiodothyronine were measured by radioimmunological assay from samples obtained from 56 patients with chronic heart failure and 19 practically healthy individuals of the control group matched by age, gender, and body mass index. Patients with low triiodothyronine syndrome were prescribed hormone replacement therapy with low doses of thyroid hormones (thyroxine 12.5-25 mcg/day) until the euthyroid state was achieved. The values of total and free triiodothyronine were significantly lower in patients with heart failure, the level of thyroxine- binding globulin was also reduced, more than twofold increase in reversible triiodothyronine level was demonstrated compared to controls. Low triiodothyronine syndrome was diagnosed in 33.9% of patients with heart failure. Hormone replacement therapy resulted in a slight improvement in contractile function in individuals with low triiodothyronine levels, 2 (10.5%) patients manifested with signs of hyperthyroidism. Advanced stages of heart failure might be linked with NTIS. Hormone replacement therapy with low doses of thyroxine can contribute to a moderate improvement in contractile function, as evidenced by the improvement in left ventricular ejection fraction.  

Keywords:  Non-thyroidal illness syndrome (NTIS),  euthyroid sick syndrome,  heart failure,  hormone replacement therapy.