Supplementary Material for: High-Normal Thyroid Function and Recurrence of Atrial Fibrillation after Catheter Ablation: A Prospective Observational Study

<b><i>Background:</i></b> Thyroid function is increasingly recognized as an important modifiable factor for atrial fibrillation (AF); however, it is unclear if the changes in thyroid hormones, even within the normal range, are associated with AF recurrence after catheter ablation. <b><i>Methods:</i></b> Consecutive paroxysmal AF patients who underwent catheter ablation were enrolled. Patients with abnormal thyroid hormones or previous thyroid illnesses were excluded. Patients were followed for 12 months or until they presented with the first episode of atrial tachyarrhythmia after a blanking period. <b><i>Results:</i></b> The study included 448 patients with a mean age of 61 (14) years, and 46% were women. After a 1-year follow-up, 104 (23.2%) patients experienced atrial tachyarrhythmia recurrences after an ablation procedure. Recurrence was significantly different among quartile groups of thyroid function, with highest FT₄ and FT₃ levels associated with the greatest risk of recurrence (<i>p</i> &lt; 0.001 and <i>p</i> = 0.024, respectively). FT₄ and FT₃ levels were independent predictors of atrial tachyarrhythmia recurrence (hazard ratio 1.07 per 1 pmol/L increase in FT₄, 95% confidence interval [CI] 1.01–1.15, <i>p</i> = 0.036 and 1.31 per 1 pmol/L increase in FT₃, 95% CI 1.01–1.71, <i>p</i> = 0.032). <b><i>Conclusions:</i></b> High-normal FT₃ and FT₄ levels are associated with AF recurrence after catheter ablation in this Chinese population. Attention to thyroid hormones could be valuable to assist in the management of AF.