Endocrine Abstracts

Introduction: Hypothyroidism has detrimental effects on the cardiovascular system but controversy remains over the benefit of levothyroxine substitution in heart failure (hf). The aim of this register based cohort study was to examine the effects of levothyroxine treatment on all-cause mortality in patients with hf.

Methods: The study cohort comprised all Danish citizens aged ≥18 years admitted with hf in 1997–2012 and still alive 30 days after discharge. Patients with a previous history of thyroid dysfunction, levothyroxine treatment, amiodarone treatment or related thyroid medication were excluded. Subsequent levothyroxine treatment was identified by individual-level linkage of nationwide registers of hospitalization and drug dispensing from pharmacies. Treated patients contributed with risk time in the untreated group and moved to the treated group when they initiated levothyroxine treatment. Patients left study at death, emigration, initiation of amiodarone treatment or end-of-study. Risk of death was analysed by calculating incidence rates per 1000 person years (PY) and incidence rate ratio (IRR) was analysed by Poisson regression models adjusted for age, gender and comorbidity.

Results: A total of 242,250 patients were admitted with hf in the study period (mean age 70.9 [S.D.±14.5] years, 53.5% male). 6,619 (2.7%) of these patients were prescribed levothyroxine after discharge. During a mean follow-up time of 7.4 years (S.D.±7.6), 167.874 (69.3%) patients died. Mortality rates were 93.4 and 139.6 deaths per 1000 PY among untreated and levothyroxine-treated patients, respectively. A 23% increased risk of all-cause mortality was found in patients substituted with levothyroxine (IRR: 1.23 [95% CI: 1.19–1.27]).

Conclusion: We found an increased risk of all-cause mortality in hf patients treated with levothyroxine compared with those without levothyroxine treatment. The impact of thyroid dysfunction on prognosis in hf and benefit or harm of thyroid hormone substitution warrants further investigation.