Short-term amiodarone treatment for atrial fibrillation after catheter ablation induces a transient thyroid dysfunction: Results from the placebo-controlled, randomized AMIO-CAT trial

•No clinical adverse effects on the thyroid were seen in patients taking amiodarone.•Amiodarone was associated with increased TSH, T4 and fT4, and decreased T3 and fT3.•In the amiodarone group, 16% had biochemical hypothyroidism after 1 month.•Thyroid dysfunction had decreased significantly 1 month after drug discontinuation.•After 4 months, there were no differences from baseline.

BackgroundAmiodarone is known to affect the thyroid, but little is known about thyroid recovery after short-term amiodarone treatment.ObjectivesWe aimed to evaluate the impact of 8 weeks of amiodarone treatment on thyroid function in patients with atrial fibrillation (AF) undergoing catheter ablation in a randomised, double-blind clinical trial.Methods212 patients referred for AF ablation at two centres were randomized to 8 weeks of oral amiodarone or placebo. Thyroid function tests (TSH, thyroid stimulating hormone; T4, thyroxine; T3, triiodothyronine; fT4, free T4; fT3, free T3) were performed at baseline and 1, 3 and 6 months.ResultsStudy drug was discontinued due to mild thyroid dysfunction in 1 patient in the placebo vs. 3 in the amiodarone group (p = 0.6). In linear mixed models there were significant effects of amiodarone on thyroid function tests, modified by follow-up visit (p < 10− 9 for both TSH, T4, T3, fT4 and fT3). The amiodarone group had higher TSH, fT4 and T4 after 1 and 3 months compared to placebo, whereas T3 and fT3 were lower. In all cases, the amiodarone-induced thyroid dysfunction was largest at 1 month, declining at 3 months, and with no differences at 6 months, compared to baseline.ConclusionWe found amiodarone to have a significant impact on thyroid function after only 1 month, but with a fast recovery of thyroid function after amiodarone discontinuation. Our study indicates that short-term amiodarone can be considered safe in patients without prior thyroid dysfunction.