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.