Evaluation of thyroid dysfunction in patients with paroxysmal atrial fibrillation

Atrial fibrillation (AF) is the most frequent cause of hospitalization for arrhythmias. The aim of our study was to evaluate the prevalence of thyroid dysfunction in patients with paroxysmal AF without any cardiomyopathy.

Two hundred sixty eight patients (164 women and 104 men, mean age 64.9+/-16.9 years) affected by paroxysmal AF entered the present study. Patients underwent routine laboratory examinations with estimation of thyroid hormones levels, standard electrocardiogram (ECG) and transthoracic echocardiography.

Thyroid stimulating hormone (TSH) levels were low (<0.3 mU/L) in 168 patients (62.7%) and high (>5 mU/L) in 39 patients (14.9%); 76 patients (28.4%) had high free triiodothyronine (FT3) levels (>4.3 pg/ml) and 91 patients (34.3%) had high free thyroxine (FT4) levels (>1.7 ng/dl); 60 patients (22.4%) had low FT3 levels (<2 pg/ml) and 24 patients (9%) had low FT4 levels (<0.9 ng/dl). Overall, 76.2% of patients with hyperthyroidism were women. Hyperthyroidism was considered subclinical in 68 (40.5%) patients with low SH concentrations.

Thyroid dysfunctions have a high prevalence in AF patients and hyperthyroidism is the most common disorder. Hyperthyroidism in AF patients more often occurs in women than in men. Any minimal but persistent modification of circulating thyroid hormone levels can favor episodes of AF; it can be useful to thoroughly assess thyroid function in all patients suffering from AF.