Mildly underactive thyroid increases heart failure risk

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Subclinical hypothyroidism may modestly increase the risk of heart failure, researchers reported at the American Thyroid Association meeting last week in New York. Patients with thyroid stimulating hormone levels of 10 mU/L or higher were at almost twice the risk of heart failure as patients without subclinical hypothyroidism.

Doug Bauer, MD, and colleagues analyzed echocardiographic heart function changes among 3,065 patients, 65 and older, who were initially free of heart failure.

During 12 years of follow-up, 660 participants (22 percent) had heart failure events, 16 percent had subclinical hypothyroidism and 1.4 percent had subclinical hyperthyroidism.

After controlling for cardiovascular risk factors, subclinical hypothyroid patients with thyroid-stimulating hormone (TSH) levels in the higher range were at a modestly elevated risk of heart failure compared with participants with normal thyroid function.

Subclinical hypothyroid patients with TSH levels in the lower range were no more likely than euthyroid participants to develop heart failure. Subclinical hyperthyroidism was not associated with more heart failure events than normal thyroid function.

Most echocardiographic parameters were not correlated with thyroid status. Patients with a TSH of at least 10 mU/L had a higher peak E velocity than those without subclinical hypothyroidism, which suggested decreased left ventricular compliance, Bauer said.

However, changes in echocardiographic parameters during six years of follow-up were not significantly associated with thyroid status.

An association between heart failure and thyroid function has been fairly well studied and it is likely that "subclinical hypothyroid state results in a less efficient contraction of the heart," Bauer said. Another possible explanation could include fluid retention, he added.

If the findings are confirmed through further studies, "it also suggests the potential that we might screen for abnormal thyroid tests to prevent people from developing heart failure in the future," he concluded.