Epidemiology

Subclinical hypothyroidism linked to heart failure

Adults with subclinical hypothyroidism are at increased risk for heart failure and for changes in cardiac function, new research suggests. Subclinical hyperthyroidism, by contrast, does not carry these risks.

Dr Nicolas Rodondi, from the University of Lausanne, Switzerland, and colleagues concluded that further studies are needed to determine if thyroxine replacement can reduce the risk of heart failure seen with subclinical hypothyroidism.

The findings, reported in the Journal of the American College of Cardiology, stem from an investigation of 3044 subjects, 65 years and older, who were free from heart failure upon enrollment in the Cardiovascular Health Study.

The subjects were classified according to thyroid test results: euthyroidism, subclinical hypothyroidism, and subclinical hyperthyroidism. Subjects in the subclinical hypothyroidism group were subdivided into groups based on whether the TSH level was 4.5 to 9.9 mU/L or 10.0 mU/L or higher.

During a mean follow-up period of 12 years, 736 subjects developed heart failure. The rate of heart failure in subclinical hypothyroid subjects with TSH levels of 10.0 mU/L or higher was 41.7 per 1000 person-years compared with a rate of 22.9 per 1000 person-years in euthyroid subjects (HR = 1.88, p= 0.01).

Echocardiographic assessment also revealed diastolic functional changes in individuals with TSH levels of 10.0 mU/L or higher, and an increase in left ventricular mass was noted in these subjects over five years of follow-up.

Neither subclinical hyperthyroidism, nor subclinical hypothyroidism with TSH levels of 4.5 to 9.9 mU/L affected the risk of heart failure or functional abnormalities, the report indicates.

Reuters