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Subclinical hyperthyroidism as a risk factor for atrial fibrillation.
J Auer1, P Scheibner, T Mische
1Division of Cardiology and Intensive Care, Department of Internal Medicine II, General Hospital Wels, Wels, Austria. johann.auer@khwels.at
American Heart Journal
|October 31, 2001
Summary
Subclinical hyperthyroidism, indicated by low thyrotropin levels, significantly increases atrial fibrillation risk. This risk is comparable to overt hyperthyroidism, highlighting the importance of monitoring thyroid function.
Area of Science:
- Endocrinology
- Cardiology
- Thyroidology
Background:
- Atrial fibrillation (AF) is a known complication of hyperthyroidism.
- Subclinical hyperthyroidism involves low serum thyrotropin (TSH) with normal free thyroid hormone levels.
- The association between subclinical hyperthyroidism and AF requires further investigation.
Purpose of the Study:
- To determine if subclinical hyperthyroidism is a risk factor for developing atrial fibrillation.
- To compare the risk of AF in individuals with subclinical hyperthyroidism versus those with normal thyroid function.
Main Methods:
- A cohort study of 23,638 individuals was conducted.
- Participants were categorized into three groups based on serum TSH and free thyroid hormone levels: normal (Group 1), overt hyperthyroidism (Group 2), and subclinical hyperthyroidism (Group 3).
- The incidence of atrial fibrillation was recorded and compared across the groups.
Main Results:
- Atrial fibrillation prevalence was 2.3% in Group 1, 13.8% in Group 2, and 12.7% in Group 3.
- Individuals with low TSH concentrations (<0.4 mU/L) had a 13.3% AF prevalence compared to 2.3% in those with normal TSH.
- Low TSH with normal thyroid hormones conferred a 5.2-fold increased risk of AF (relative risk = 5.2; 95% CI 2.1-8.7).
Conclusions:
- Low serum TSH concentration is a significant risk factor for atrial fibrillation.
- The likelihood of AF is over 5 times higher in individuals with low TSH, regardless of overt or subclinical hyperthyroidism.