Thyroid Function in 3000 Cases of Patients With Atrial Fibrillation Treated With Catheter Ablation

Objective: Thyroid hormones have various effects on cardiac and circulatory systems, leading to arrhythmias and heart failure. In Europe and the United States, it has been reported that elevated thyroid hormones within the normal range have been reported to be associated with a risk of atrial fibrillation, however, there was no report on Japanese cases, a country that differs in iodine intake and ethnicity from the West. Therefore, we evaluated the abnormality of thyroid function in a large number of cases of atrial fibrillation (AF) who received catheter ablation (RFCA) in Japan. Methods: We evaluated 2,937 cases of atrial fibrillation (2,084 males, mean age 64.1±10.7 years and 853 females, 69.0±8.5 years) who underwent RFCA at the Gunma Prefectural Cardiovascular Center between 2012 and 2018. As a control we used a total of 15,660 participants for health check-up (9,176 males, mean age 49.7±9.8 years and 6,484 females, 48.9±10.3 years) from 2006 to 2013, and we evaluated thyroid function after adjusting for gender-specific age. Results: The prevalence of overt hyperthyroidism was significantly higher in the RFCA-treated male group (0.43%) than in the control group (0.07%), even after adjusting for age (p<0.01). Similarly, the prevalence of subclinical hyperthyroidism was also significantly higher in the RFCA-treated male group (3.12%) than in the control group (0.94%) after adjusting for age (p<0.01). On the other hand, subclinical hypothyroidism was significantly lower in the RFCA-treated group after adjusting for age (2.97% in the RFCA-treated group and 3.93% in the control group, p<0.01). Females showed the same results as males. Conclusions: In an iodine rich country Japan, not only overt hyperthyroidism but also subclinical hyperthyroidism is an obvious risk factor for severe atrial fibrillation in Japan. Intriguingly, subclinical hypothyroidism might contribute to the prevention of atrial fibrillation, suggesting that slightly higher serum TSH levels might be better for elderlies.