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Mildly Underactive Thyroid Increases Heart Failure
Risk
NEW YORK, 3-20-08-- Subclinical hypothyroidism may modestly increase the risk of
heart failure, researchers reported here.
Asymptomatic 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, found a large cohort study presented at the American
Thyroid Association meeting.
This risk is comparable to that from diabetes and hypertension, both known heart
failure risk factors, said Doug Bauer, M.D., of the University of California at
San Francisco.
The study excluded patients who were taking thyroid hormones, but Dr. Bauer said
the results suggested that treating subclinical hypothyroidism could reduce
heart failure risk.
"When we included people treated during follow-up," he said, "the risk of heart
failure was attenuated compared with those not treated."
However, he cautioned that the study was not designed to answer that question,
and further study is needed.
"People who have heart failure should be evaluated to make sure that their
thyroid tests, specifically their TSH, are normal," Dr. Bauer added.
Previous studies linked overt hyperthyroidism and hypothyroidism to heart
problems. The Health Aging and Body Composition (Health ABC) study had shown a
similar relationship for subclinical hypothyroidism, but without confirmation of
the heart abnormalities on echocardiogram.
So Dr. Bauer's group analyzed echocardiographic heart function changes among
3,065 patients 65 and older in the Cardiovascular Health Study who were
initially free of heart failure.
During 12 years of follow-up, 660 participants (22%) had adjudicated heart
failure events, 16% had subclinical hypothyroidism (TSH levels 4.5 mU/L or
higher but normal free thyroxine levels), and 1.4% had subclinical
hyperthyroidism (TSH less than 0.45 mU/L).
After controlling for cardiovascular risk factors, including hypertension and
diabetes, subclinical hypothyroid patients with TSH levels in the higher range
(10 mU/L or greater) were at a modestly elevated risk of heart failure compared
with participants with normal thyroid function (hazard ratio 1.88, 95%
confidence interval 1.05 to 3.34, P=0.003).
However, subclinical hypothyroid patients with TSH levels in the lower range
(4.5 to 9.9 mU/L) were no more likely than euthyroid participants to develop
heart failure in the multivariate analysis (HR 0.92, 95% CI 0.73 to 1.17).
Subclinical hyperthyroidism was not associated with more heart failure events
than normal thyroid function (HR 0.94, 95% CI 0.48 to 1.83).
Although most baseline echocardiographic parameters were not correlated with
thyroid status, patients with a TSH of at least 10.0 mU/L had a higher peak E
velocity than those without subclinical hypothyroidism (0.80 versus 0.72 m/sec,
P=0.002), which suggested decreased left ventricular compliance, Dr. Bauer said.
This was associated with incident heart failure in the overall cohort.
However, changes in echocardiographic parameters during six years of follow-up
for this measure were not significantly associated with thyroid status.
The mechanism for 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," Dr. Bauer said. Another
possible explanation could include fluid retention, he said.
If the findings are confirmed, "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.
For all thyroid news, free thyroid hormone test, and complete information: visit Thyroid 101.