Amiodarone-induced thyroid dysfunction and ventricular tachyarrhythmias during long-term therapy in Japan

In 232 Japanese patients receiving long-term amiodarone therapy for life-th reatening ventricular tachyarrhythmias, hyperthyroidism and hypothyroidism developed in 29 patients (12.5%) and 25 patients (10.8%), respectively. In patients with hyperthyroidism. the recurrence of sustained ventricular tach ycardia was significantly higher with thyrotoxicosis than in the euthyroid period (31% vs 3%, p<0.01). Holter monitoring showed that the average heart rate and ventricular premature complexes significantly increased with hype rthyroidism. On the other hand, there was no increase in the recurrence of ventricular tachyarrhythmia with hypothyroidism. There was no change in the dose or the plasma concentration of amiodarone or desethylamiodarone in th e euthyroid period or when hyperthyroidism or hypothyroidism manifested. It is important to monitor for arrhythmia when hyperthyroidism develops durin g amiodarone therapy.