Subclinical hyperthyroidism associated with CHD risk, afib risk, total mortality, study indicates

Subclinical hyperthyroidism is associated with increased risk for total mortality, coronary heart disease (CHD) mortality, and incident atrial fibrillation, according to a new study.

Researchers examined pooled individual data from 52,674 participants in 10 large, prospective cohorts to determine the association between endogenous subclinical hyperthyroidism and risks of total and CHD death, CHD events, and atrial fibrillation. Six cohorts had data available on CHD events in 22,437 participants, and five cohorts had data available on incident atrial fibrillation in 8,711 participants. The median age of participants was 59 years, and 58.5% were women. The authors defined euthyroidism as a thyrotropin level of 0.45 mIU/L to 4.49 mIU/L and endogenous subclinical hyperthyroidism as a thyrotropin level below 0.45 mIU/L with normal free thyroxine levels when participants taking thyroid-altering medications were excluded. The study results were published online April 23 by Archives of Internal Medicine.

A total of 2,188 (4.2%) of the 52,674 participants had endogenous subclinical hyperthyroidism. Overall, 8,527 participants died during follow-up, 1,896 from CHD. CHD events occurred in 3,653 of 22,437 participants and atrial fibrillation developed in 785 of 8,711 participants. Subclinical hyperthyroidism was found to be associated with increased total mortality, CHD mortality, CHD events and atrial fibrillation in analyses adjusted for age and sex. No differences in risk were seen by age, sex or preexisting cardiovascular disease, and risk remained similar after adjustment for cardiovascular risk factors. Participants with a thyrotropin level below 0.10 mIU/L had a higher risk for CHD death and atrial fibrillation than those with a thyrotropin level between 0.10 and 0.44 mIU/L.

The authors acknowledged that their study involved mainly white participants, that thyroid function was tested only at baseline, and that other conditions that could have affected mortality were not assessed, among other limitations. However, they concluded that an association exists between endogenous subclinical hyperthyroidism and risk for total mortality, CHD mortality and incident AF. Risks for CHD mortality and atrial fibrillation are highest with a thyrotropin level below 0.10 mIU/L, they noted.

An accompanying editorial also noted the study's limitations but said it provides important information about the importance of subclinical hyperthyroidism in clinical practice. “Until further data are available, the relationship between subclinical hyperthyroidism and increased mortality, CHD mortality and atrial fibrillation presently provides sufficient evidence to consider treatment of subclinical hyperthyroidism, especially in elderly patients with cardiac risks, hyperthyroid symptoms, or osteoporosis,” the editorialist wrote.