Impaired sensitivity to thyroid hormones is associated with atrial fibrillation in the euthyroid population

Background The relationship between thyroid hormone sensitivity and atrial fibrillation (AF) progression remains unclear. Objective This study aimed to investigate the relationship between impaired thyroid hormone sensitivity and the progression of AF in individuals with normal thyroid function. Methods This retrospective cross-sectional study included 1,190 consecutive patients with AF, who were classified into paroxysmal AF ( n = 623) and persistent AF ( n = 567) groups. Data on cardiac ultrasound and serum biochemical parameters were obtained. Thyroid hormone sensitivity was assessed using a parametric thyroid feedback quantile-based index (PTFQI), thyrotropin-thyroxine resistance index (TT4RI), and peripheral free triiodothyronine/free thyroxine (FT3/FT4) ratio. Logistic regression analysis was performed to assess the relationship between thyroid hormone sensitivity indices and AF classification. Results Compared with the paroxysmal AF group, patients with persistent AF exhibited significantly higher PTFQI and TT4RI values and a lower FT3/FT4 ratio ( P for trend <0.001). In the multivariable logistic regression analysis, persistent AF was independently and significantly associated with elevated TT4RI and PTFQI as well as a reduced FT3/FT4 ratio (all P for trend <0.05). In the fully adjusted model, the odds ratios (95% confidence intervals) for TT4RI, PTFQI, and FT3/FT4 ratios were 1.038 (1.010–1.066), 4.063 (1.527–10.809), and 0 (0–0.071), respectively. Quartile-based analysis further revealed a consistent and significant association between higher PTFQI scores and the probability of persistent AF across all upper quartiles ( P < 0.01). The FT3/FT4 ratio demonstrated a non-linear association with persistent AF, acting as a risk factor in the third quartile (Q3, P for trend = 0.018) and as a protective factor in the fourth quartile (Q4, P for trend = 0.003). No statistically significant differences were observed between TT4RI quartiles. Conclusion Impaired thyroid hormone sensitivity may contribute to the progression from paroxysmal to persistent AF in euthyroid patients; however, its clinical predictive value requires further validation in large-scale studies.