Prognostic impact of subclinical thyroid dysfunction in heart failure

Abstract

Background: Therapeutic and prognostic implications of subclinical thyroid dysfunction in patients with heart failure (HF) are unclear. We compared the prognostic impact of euthyroidism, subclinical thyroid dysfunction, and euthyroid sick syndrome (ESS) in systolic HF.

Methods: We included 1032 patients hospitalized for systolic HF (left ventricular ejection fraction [LVEF] ≤40%) who participated in a randomized trial assessing the effects of a HF disease management program. Patients with incomplete thyroid function tests or thyrotropic medication were excluded. In the remaining 758 subjects, the risk of all-cause death was estimated based on TSH only, or full thyroid function profile. Changes of thyroid function after six months were assessed in 451 subjects.

Results: Subclinical thyroid dysfunction was present in 103 patients at baseline (14%). No differences were found between groups regarding NYHA class (P=0.29), and LVEF (P=0.60). After a median follow-up of three years patients with ESS (n=13) had a 3-fold age-adjusted increased risk of death compared to euthyroid patients (P=0.001). However, neither subclinical hyperthyroidism (HR 1.18, 95%CI:0.82-1.70) nor hypothyroidism (HR 1.07, 95%CI:0.58-1.98) were associated with increased age-adjusted mortality risk. Subclinical thyroid dysfunction had normalized spontaneously at follow-up in 77% of patients. However, persistent subclinical thyroid dysfunction was also not associated with worse outcome.

Conclusions: In this large well-characterized HF cohort, subclinical thyroid dysfunction did not predict an increased mortality risk. Thus, in patients with moderate to severe HF, further diagnostic and therapeutic procedures for subclinical thyroid dysfunction appear dispensable. ESS was an infrequent but important indicator of a poor prognosis in HF.

Clinical trial registration url: http://www.controlled-trials.com. Unique identifier: ISRCTN23325295.

Keywords: Chronic heart failure; Euthyroid sick syndrome; Prognosis; Subclinical hyperthyroidism; Subclinical hypothyroidism; Thyroid dysfunction.