Subclinical Thyroid Dysfunction, Cardiac Function, and the Risk of Heart Failure

OBJECTIVES The goal of this study was to determine whether subclinical thyroid dysfunction was associated with incident heart failure (HF) and echocardiogram abnormalities. BACKGROUND Subclinical hypothyroidism and hyperthyroidism have been associated with cardiac dysfunction. However, long-term data on the risk of HF are limited. METHODS We studied 3044 adults ≥65 years initially free of HF in the Cardiovascular Health Study (CHS). We compared adjudicated HF events over a mean 12-year follow-up and changes in cardiac function over 5 years among euthyroid participants, those with subclinical hypothyroidism (subdivided by TSH levels: 4.5–9.9, ≥10.0 mU/L), and those with subclinical hyperthyroidism. RESULTS Over 12 years, 736 participants developed HF events. Participants with TSH≥10.0 mU/L had a greater incidence of HF compared to euthyroid participants (41.7 vs. 22.9/1000 person years, p=0.01, adjusted hazard ratio=1.88, 95% confidence interval 1.05–3.34). Baseline peak E velocity, an echocardiographic measurement of diastolic function associated with incident HF in the CHS cohort, was higher in those with TSH≥10.0 compared to euthyroid participants (0.80 vs. 0.72 m/sec, p=0.002). Over 5 years, left ventricular mass increased among those with TSH≥10.0, but other echocardiographic measurements were unchanged. Those with TSH 4.5–9.9 or with subclinical hyperthyroidism had no increase in risk of HF. CONCLUSIONS Compared to euthyroid older adults, those with a TSH≥10.0 mU/L have a moderately elevated risk of HF and alterations in cardiac function, but not older adults with TSH<10. Clinical trials should assess whether the risk of HF might be ameliorated by thyroxine replacement in individuals with TSH≥10.0 mU/L.