Overactive thyroid associated with abnormal heart rhythm, but not other cardiovascular problems

February 28, 2006

Having an overactive thyroid gland is linked with an increased risk for atrial fibrillation (a type of abnormal heart rhythm), but neither an over- or under active thyroid gland is associated with a higher risk for other cardiovascular problems or increased risk of death, according to a study in the March 1 issue of JAMA.

Thyroid hormone excess and deficiency are common, and can be readily diagnosed and treated. Previous studies have suggested that abnormal levels of thyroid stimulating hormone (TSH) may represent a cardiac risk factor. Cardiovascular diseases (CVD) are the most common cause of death in the U.S. Even mildly altered thyroid status reportedly affects serum cholesterol levels, heart rhythm and rate, ventricular function, risk of coronary artery disease, and cardiovascular death. However, the relationship between abnormal thyroid function and cardiovascular outcomes remains unclear, according to background information in the article.

Anne R. Cappola, M.D., Sc.M., of the University of Pennsylvania School of Medicine, Philadelphia, and colleagues tested the hypothesis that abnormal thyroid status is associated with increased cardiovascular risk and death in individuals with unrecognized thyroid dysfunction. The study included 3,233 U.S. individuals aged 65 years or older who had their serum thyroid-stimulating hormone levels measured when enrolled in 1989-1990. The cardiovascular health of the patients, who were not taking thyroid medication, was assessed through June 2002.

The researchers found that 82 percent of participants had normal thyroid function, 15 percent had subclinical (before symptoms) hypothyroidism (an underactive thyroid gland), 1.6 percent had symptomatic hypothyroidism, and 1.5 percent had subclinical hyperthyroidism (an overactive thyroid gland). After exclusion of those who had atrial fibrillation at the start of the study, individuals with subclinical hyperthyroidism had nearly twice the incidence of developing atrial fibrillation compared with those with normal thyroid function. No differences were seen between the subclinical hyperthyroidism group and the normal thyroid function group for the occurrence of coronary heart disease, cerebrovascular disease, cardiovascular death, or all-cause death. Likewise, there were no differences between the subclinical hypothyroidism or symptomatic hypothyroidism groups and the normal thyroid function group for cardiovascular outcomes or death.

"Our analyses do not support screening older individuals solely to prevent atrial fibrillation, with an estimated number needed to screen of 2,500 older individuals to find 1 case of atrial fibrillation associated with subclinical hyperthyroidism. Our findings suggest that if endogenous [originating from within the thyroid] subclinical hyperthyroidism is detected, older individuals may benefit from treatment to prevent atrial fibrillation," the authors write. "Our analyses do not support screening older individuals for thyroid disease to prevent CVD, and, although our data are observational, they do not support treatment of individuals with subclinical hypothyroidism to prevent cardiovascular events."
-end-
(JAMA. 2006;295:1033-1041. Available pre-embargo to the media at www.jamamedia.org)

Editor's Note: For funding/support information, please see the JAMA article.

The JAMA Network Journals

Related Atrial Fibrillation Articles from Brightsurf:

Atrial fibrillation less deadly than it used to be, but still cause for concern: BU study
A first-of-its-kind study by researchers from the Boston University School of Public Health (BUSPH) shows a decline in deaths related to atrial fibrillation (irregular heartbeat) over the last 45 years.

Postoperative atrial fibrillation does not impact on overall survival after esophagectomy
Volume 11, Issue 25 of Oncotarget reported that Administration of landiolol hydrochloride was found to be associated with reduced incidence of atrial fibrillation after esophagectomy for esophageal cancer in our previous randomized controlled trial.

People with atrial fibrillation live longer with exercise
More than 100,000 Norwegians have atrial fibrillation. They should be actively exercising for their health.

Atrial fibrillation among overweight people is not due to fat
In a recently published study, researchers from Aarhus University document that the risk of atrial fibrillation is not linked to the amount of body fat, but instead to large muscle mass, or more precisely, a high fat-free weight

Eating more protein could help ward off atrial fibrillation in women
Women who ate slightly more than the recommended daily amount of protein were significantly less likely to develop atrial fibrillation (AFib), a dangerous heart rhythm disorder that can lead to stroke and heart failure, when compared with those who consumed less protein, according to research being presented at the American College of Cardiology's Annual Scientific Session Together with World Congress of Cardiology (ACC.20/WCC).

Zebrafish teach researchers more about atrial fibrillation
Genetic research in zebrafish at the University of Copenhagen has surprised the researchers behind the study.

Personalized medicine for atrial fibrillation
The study, published in Europace, uses signals from implantable devices -- pacemakers and defibrillators -- to analyze electrical signals in the heart during episodes of atrial fibrillation.

Prescribing anticoagulants in the ED for atrial fibrillation increases long-term use by 30%
Patients prescribed anticoagulants after a diagnosis of atrial fibrillation in the emergency department are more likely to continue long-term use of medications to treat the condition, according to research published in CMAJ (Canadian Medical Association Journal).

Anticoagulant benefits for atrial fibrillation decrease with age
The net clinical benefit of anticoagulants for atrial fibrillation (AF) -- one of the most important causes of irregular heartbeats and a leading cause of stroke -- decreases with age, as the risk of death from other factors diminishes their benefit in older patients, according to a study led by researchers at UC San Francisco.

Research improves understanding of mechanism of atrial fibrillation
Mouse model studies show that noncoding DNA regions linked to atrial fibrillation risk can display long-range regulatory functions directed at Pitx2 gene and in this way predispose to the condition.

Read More: Atrial Fibrillation News and Atrial Fibrillation Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.