BACKGROUND: Changes in peripheral thyroid hormone concentration and metabolism 
can occur in euthyroid patients suffering from severe non-thyroidal illnesses. 
Recently, sick euthyroid syndrome has been reported in patients suffering from 
advanced heart failure.
AIM: This study was to evaluate prospectively the presence and 
pathophysiological implications of sick euthyroid syndrome in moderate-to-severe 
chronic heart failure patients.
METHODS: The study population were 199 chronic heart failure patients admitted 
over a 2-year period to our heart failure unit for assessment of cardiac 
transplantation. They were closely followed up with clinical and instrumental 
examinations (including clinical, hormonal, nutritional and cardiac function 
evaluations). Sick euthyroid syndrome was defined as a serum total 
triiodothyronine value of less than the lowest normal limit (< 1.23 nmol.l-1) in 
the presence of a normal serum thyroid stimulating hormone concentration.
RESULTS: Sick euthyroid syndrome was found in 36/199 patients (18%). According 
to the New York Heart Association (NYHA) classification of severity of heart 
failure, sick euthyroid syndrome patients appear in higher NYHA classes (31% of 
classes III and IV, vs 7% of class I and II). Such patients also weigh less and 
are more frequently malnourished. Alterations in cardiac index, ventricular 
filling pressures, functional impairment, and the liver function parameters, 
were more significant in sick euthyroid syndrome than in non-sick euthyroid 
syndrome patients. Serum norepinephrine and atrial natriuretic factor were 
significantly higher, and insulin significantly lower in the sick euthyroid 
syndrome group. During follow-up, deaths were significantly more frequent in 
sick euthyroid syndrome patients (13/27, 48%) than in non-sick euthyroid 
syndrome (30/141, 21%; P < 0.005). In six sick euthyroid syndrome patients who 
underwent heart transplantation, mean total triiodothyronine values increased 
from 0.9 +/- 0.1 before to 1.96 +/- 0.3 nmol.l(-1)post-transplantation (P < 
0.05).
CONCLUSIONS: In a large and representative population of patients with 
moderate-to-severe heart failure, sick euthyroid syndrome shows a prevalence of 
18%. Its occurrence was related to the degree of functional cardiac impairment, 
but was not an independent negative prognostic factor. Preliminary results 
indicate that heart transplantation is associated with reversibility of sick 
euthyroid syndrome.