Long-Term Outcome in Levothyroxine Treated Patients With Subclinical Hypothyroidism and Concomitant Heart Disease

Context: Subclinical hypothyroidism is a common condition that may lead to impaired cardiac function. Objective: This study sought to examine the effects of levothyroxine treatment in patients with subclinical hypothyroidism and heart disease. Design: This was a register-based historical cohort study. Setting and Participants: The study was composed of Danish primary care patients and hospital outpatients age 18 years and older with established heart disease who were diagnosed with subclinical hypothyroidism in 1997–2011. Patients were stratified according to whether they claimed a subsequent prescription of levothyroxine. Event rates and incidence rate ratios (IRR) were calculated by use of time-dependent multivariable Poisson regression models. Main Outcome Measures: Measures included all-cause mortality and major adverse cardiac events (MACEs), defined as cardiovascular death, fatal or nonfatal myocardial infaction and stroke, and all-cause hospital admissions. Results: Of 61 611 patients with a diagnosis of cardiac disease having their first time thyroid function testing, 1192 patients with subclinical hypothyroidism (mean age 73.6 [SD ± 13.3] y, 63.8% female) were included, of whom 136 (11.4%) were treated with levothyroxine. During a median follow-up time of 5.6 y (interquartile range, 6.5 y), 694 (58.2%) patients died. Patients treated with levothyroxine displayed no significantly increased risk of all-cause mortality (adjusted IRR, 1.17; 95% confidence interval [CI], 0.90–1.52), MACE (adjusted IRR, 1.08; 95% CI, 0.80–1.45), or hospital admission (adjusted IRR, 0.94; 95% CI, 0.71–1.24), when compared with patients not treated with levothyroxine. Conclusion: Levothyroxine treatment in patients with subclinical hypothyroidism and heart disease was not associated with a significant benefit nor risk of all-cause mortality, MACE, or hospital admission in this large real-world cohort study. We studied levothyroxine treatment in patients with subclinical hypothyroidism and heart disease and found no association between treatment and risk of all-cause mortality, MACE or hospital admission.