Background. It is evident, that overt thyroid dysfunction (both, hypo- or hyperthyroidism) could be associated with heart failure. The aim of our study was to establish whether also mild changes in free thyroxin (fT4) may influence the degree of heart failure in patients with chronic heart insufficiency. Methods and Results. There were included 148 patients (m 121, f 27, mean age 63,8±1,14) with clinical chronic heart failure were, with fT4 levels within the normal range (9-22 pmol/l) and without thyroid suppression or substitution treatment. Degree of heart failure was quantified by plasma B-type natriuretic peptide (BNP), N-terminal pro-BNP (NT-proBNP) and big endothelin. Patients with fT4 in the range 11,9–14,6 pmol/l (optimal, 3rd-6th decile) had significantly lower NT-proBNP (718±70,4 pg/ml), than those with fT4 <11,8 (low-normal, bottom two deciles) (1236±223,6 pg/ml; p<0,03) and those with fT4 over 14,6 pmol/l [high-normal, top four deciles] (1192±114,9 pg/ml; p<0,0002). These differences remain significant also if adjusted for age, gender and other confounders; adjusted odds ratio was 1,30 (1,05–1,59) for optimal vs. low-normal and 1,27 (1,04–1,55) for optimal vs. high-normal. Similar statistical differences were found also in BNP and high endothelin, but only between optimal and high-normal fT4 strata. Conclusions. The degree of heart failure could be influenced also by mild changes in fT4 concentration.

        Key words: thyroid, dysfunction, heart failure.