Elderly patients with subclinical hypothyroidism have a higher rate of congestive heart failure than do those who are euthyroid, according to Dr. Nicolas Rodondi, of the University of California, San Francisco, and associates.
Overt hypothyroidism is known to be associated with cardiovascular disease (CVD), but studies evaluating a possible link between subclinical hypothyroidism and CVD have produced conflicting results. Dr. Rodondi and his associates conducted what they described as the first prospective study to assess the risk of congestive heart failure (CHF) events in subjects with subclinical hypothyroidism.
The investigators assessed thyrotropin levels in 2,730 men and women aged 70-79 years who were participating in a large cohort study of aging. The subjects were followed for 4 years to determine whether these hormone levels were related to CHF or other cardiovascular disease events.
A total of 338 subjects (12.4%) were found to have subclinical hypothyroidism, defined as an elevated level of thyrotropin and a normal level of free thyroxine (T4). During follow-up, 178 subjects had CHF events (Arch. Intern. Med. 2005;165:2460-6).
Subjects with moderately to severely elevated thyrotropin levels (7.0 mIU/L or greater) had more CHF events (35.0 per 1,000 person-years) than did those who were euthyroid (16.5 per 1,000 person-years). Each standard deviation increase of 4.0 mIU/L was associated with a 30% increase in CHF events.
This link was even stronger among subjects known to have had previous CHF events. The rate of recurrent CHF events was seven times higher in those with subclinical hypothyroidism than in those who were euthyroid.
In contrast, subjects with mildly elevated thyrotropin (4.5-6.9 mIU/L) did not have higher rates of CHF events. Subclinical hypothyroidism was not found to be associated with other coronary heart disease events, stroke, peripheral arterial disease, CVD-related mortality, or total mortality.
In an editorial accompanying this report, Dr. Lawrence M. Crapo, of Santa Clara Valley Medical Center, San Jose, Calif., noted that these findings “certainly support the idea that the treatment of severe subclinical hypothyroidism with levothyroxine in patients younger than 80 years may be beneficial, but this remains to be proved in a randomized prospective therapeutic trial.”
The results further indicate that patients with mild hypothyroidism probably would not benefit from such treatment, Dr. Crapo said (Arch. Intern. Med. 2005;165:2451-2).