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Overactive thyroid glands increase risk for developing AF
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Patients who do not show signs of hyperthyroidism but have slightly overactive thyroid glands appear to be at risk for developing atrial fibrillation.
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% men) who consulted their general practitioner from 2000 to 2009. To analyze AF risk, 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.
“This is the first study to investigate the relationship between thyroid dysfunction and the risk of AF in a very large group of primary care patients,” Selmer said. “We have found that there is a physiological relationship between all levels of thyroid dysfunction and the risk of AF, 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 underactive thyroid glands.”
Of the 525,100 patients studied, 96% were euthyroid; 0.3% had clinical hypothyroidism; 2% had subclinical hypothyroidism; 0.7% had clinical hyperthyroidism; and 1% had subclinical hyperthyroidism.
Patients with TSH levels <0.1 mU/L had an 80% increased risk for developing AF and those with levels between 0.1 mU/L and 0.2 mU/L had a 50% increased risk. Patients who showed a higher range of “normal” TSH levels of 0.2 mU/L to 0.4 mU/L, had a 30% increased risk.
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 underactive and overactive thyroid glands and blood clots, death from CVD, and deaths from any cause in the same group of patients.
The data were presented at the Joint 15th International Congress of Endocrinology/14th European Congress of Endocrinology Meeting.
For more information:
Selmer C. Abstract OC11.2. Presented at: The Joint 15th International Congress of Endocrinology and 14th European Congress of Endocrinology Meeting 2012; May 5-9, 2012; Florence, Italy.
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Richard J. Robbins, MD, FACP
This study highlights the fact that AF might be the first and only clinical manifestation of hyperthyroidism in older individuals. This relationship is well established, and was first reported in 1951.
In 1994, Sawin et al reported that the incidence of AF was three times higher in older individuals who had low TSH levels compared with those who had normal TSH levels. In 2001, Auer et al studied 23,000 patients with true subclinical hyperthyroidism and found that the incidence of AF was five times higher than those who had normal TSH levels. Many other smaller studies have confirmed this relationship. Overall, this recent study confirms earlier observations that all patients with new onset AF should have their thyroid hormone levels checked.
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