Does link between subclinical hyperthyroidism and atrial fibrillation risk warrant screening?

Results of a population-based study support an association between subclinical hyperthyroidism with atrial fibrillation as assessed by resting ECG, even in euthyroid subjects with normal serum thyrotropin (TSH).Studies have shown that an association exists between subclinical hyperthyroidism on cardiac function or morphology. More recently, a small number of studies have emerged that provide evidence for an association between subclinical hyperthyroidism and atrial fibrillation. Researchers from the University of Birmingham examined this relationship to assess whether screening or treatment is warranted.They examined a large community-based cohort (n = 5860) of subjects aged 65 years or older (excluding those being treated for thyroid dysfunction, a previous history of hyperthyroidism and documented major risk factors for atrial fibrillation). Participants were tested for thyroid function (serum free thyroxine [T4] and TSH) and the presence of atrial fibrillation as assessed by resting 12-lead ECG.The results revealed an association between atrial fibrillation as determined by resting ECG and serum free T4; even in patients who were deemed to be euthyroid with normal serum TSH concentrations. They noted that even when previously recognised risk factors were taken into consideration, serum free T4 was an independent predictor of the presence of atrial fibrillation in the cohort, and that this association was sustained after exclusion of those with overt thyroid dysfunction. Furthermore, when the analysis was restricted to subjects classified as euthyroid (with normal serum TSH concentration), this independent relationship between serum free T4 and atrial fibrillation remained."In euthyroid subjects with normal TSH values, the finding of higher risk of atrial fibrillation in those with high but normal serum free T4 concentrations raises intriguing new questions about reducing risk of this important and common dysrhythmia in the general population," they stated.Thus, the authors concluded that their findings warrant further assessment as to the value of screening at-risk populations such as the elderly, who are known to have a higher prevalence of undetected thyroid function.Reference...