May 14, 2012
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Overactive thyroid glands put patients at increased risk for developing AF

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Patients who did not show signs of hyperthyroidism, but had slightly overactive thyroid glands were at risk for atrial fibrillation, according to data presented at the Joint 15th International Congress of Endocrinology and 14th European Congress of Endocrinology Meeting.

Using nationwide registries, Christian Selmer, MD, a research fellow at Gentofte University Hospital in Copenhagen, Denmark, and colleagues, identified individual-level linkage among 525,100 patients (mean age, 51.7 years; 39.5% male) who consulted their general practitioner from 2000-2009.

“This is the first study to investigate the relationship between thyroid dysfunction and the risk of atrial fibrillation in a very large group of primary care patients. We have found that there is a physiological relationship between all levels of thyroid dysfunction and the risk of atrial fibrillation, with a higher risk in patients with overactive thyroid glands, even when the condition is very mild or at the high end of ‘normal,’ and a lower risk in patients with under-active thyroid glands,” Selmer said.

To analyze risk for AF, researchers used cumulative incidence plots and Poisson regression models to determine Incidence Rate Ratios (IRR). Tests included measuring thyroid stimulating hormone (TSH) in the blood.

Of the 525,100 patients in the study population, 504,113 (96%) were euthyroid, 1,474 (0.3%) patients had clinical hypothyroidism, 10,679 (2%) patients had subclinical hypothyroidism, 3,421 (0.7%) had clinical hyperthyroidism and 5,414 (1%) had subclinical hyperthyroidism.

Researchers concluded that patients with TSH levels ,0.1 and between 0.1 mU/L and 0.2 mU/L had a 1.8 (80%) and 1.5 (50%) increased risk for AF, while those who showed a higher range of “normal” TSH levels of 0.2 mU/L to 0.4 mU/L, had an increased risk of 1.3 (30%).

Selmer and colleagues said they found clinical and subclinical hypothyroidism related to a lower risk for AF, while subclinical hyperthyroidism and “high-normal” thyroid function levels displayed a significant risk factor for AF.

Further studies will examine the link between under- and overactive thyroid glands and blood clots, death from heart disease and deaths from any cause in the same group of patients.

Disclosure: The researchers report no relevant financial disclosures.