NEW YORK (Reuters Health) – 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.

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

The findings, reported in the Journal of the American College of Cardiology for September 30, 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 divided into three main groups based on 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 5 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.

Reference:
J Am Coll Cardiol 2008;52:1152-1159.