The aim of this study was to evaluate the prognostic role of subclinical hypothyroidism in patients with chronic heart failure (CHF). We evaluated 338 consecutive outpatients (260 male; age 64±13) with stable CHF (NYHA class 2.3±0.6) receiving conventional therapy (ACE inhibitors and/or ARBs 93%, Beta-blockers 88%, Digitalis 26%, Diuretics 85%, Spironolactone 54%, Amiodarone 32%). The patients underwent a physical examination, electrocardiography and echocardiography. Blood samples were drawn to assess renal function, and Na+, haemoglobin, NT-proBNPs, fT3, fT4 and TSH levels.
Results: TSH levels >5.5 mIU/l were found in 34 patients (10%): none of these had low fT4 levels even though they show fT3 and fT4 values lower than subjects with normal TSH values. The patients with sub-clinical hypothyroidism were older, more frequently affected by diabetes and atrial fibrillation, and often treated with amiodarone; they had higher mean NYHA class, worse renal function, and lower mean arterial pressure. During the follow-up (mean 15±8 months; median 16 months), the progression of heart failure led to the hospitalization of 79 patients, of whom 18 died after hospitalization and six underwent transplantation. One patient experienced sudden death, and three died of non-cardiac causes. At univariate analysis, progression was significantly associated with age, diabetes, NYHA class, mean arterial pressure, heart rate, atrial fibrillation, LVEF, LVEDD, MR, GFRc, hemoglobin, natremia, NT-proBNP, the absence of ACE inhibitor/ARB therapy, and the absence of beta-blocker therapy. Furthermore, univariate regression analysis showed that TSH (P<0.0001), fT3 (P<0.0001), fT4 (P=0.016) and fT3/fT4 (P<0.0001) were associated with heart failure progression but multivariate analysis showed that only TSH considered as a continuous variable (P=0.001) as well as subclinical hypothyroidism (TSH>5.5 mUI/l; P=0.014) remained significantly associated with the events as did mean arterial pressure (P=0.003), NYHA class (P<0.001), heart rate (P<0.0001), natremia (P=0.041), and NT-proBNP (<0.0001).
Conclusions: In CHF patients TSH levels even slightly above normal range are independently associated with a greater likelihood of heart failure progression. Routinely monitoring of TSH could be useful to identify high risk patients and to improve their prognosis through levothyroxine administration.