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

Area of Science:

• Cardiology
• Endocrinology
• Pharmacology

Background:

• Amiodarone is a widely used antiarrhythmic drug for life-threatening ventricular tachyarrhythmias.
• Thyroid dysfunction, including hyperthyroidism and hypothyroidism, is a known side effect of amiodarone therapy.
• The impact of amiodarone-induced thyroid dysfunction on arrhythmia recurrence requires further investigation.

Purpose of the Study:

• To investigate the incidence of amiodarone-induced hyperthyroidism and hypothyroidism in Japanese patients.
• To evaluate the effect of these thyroid dysfunctions on the recurrence of ventricular tachyarrhythmias.
• To assess changes in amiodarone and desethylamiodarone plasma concentrations during thyroid dysfunction.

Main Methods:

• A retrospective study of 232 Japanese patients on long-term amiodarone therapy.
• Monitoring for hyperthyroidism and hypothyroidism development.
• Assessing recurrence of sustained ventricular tachycardia and Holter monitoring parameters (heart rate, ventricular premature complexes).
• Measuring plasma concentrations of amiodarone and desethylamiodarone.

Main Results:

• Hyperthyroidism developed in 12.5% and hypothyroidism in 10.8% of patients.
• Recurrence of sustained ventricular tachycardia was significantly higher in patients with hyperthyroidism (31%) compared to the euthyroid state (3%).
• Hyperthyroidism was associated with increased heart rate and ventricular premature complexes; hypothyroidism showed no such association.
• Amiodarone and desethylamiodarone plasma levels remained unchanged during thyroid dysfunction.

Conclusions:

• Hyperthyroidism is a significant risk factor for arrhythmia recurrence in patients on amiodarone therapy.
• Hypothyroidism does not appear to increase arrhythmia recurrence.
• Close monitoring for arrhythmia is crucial when hyperthyroidism develops during amiodarone treatment.