Thyroid Research Thyroid Research Archive Hyperthyroidism

Recurrence of cardiac rhythm abnormalities in patients with hyperthyroidism caused by amiodarone

(March 2002)

The background of the study. Many patients with ventricular tachycardia (rapid contractions of the ventricles of the heart) are treated with amiodarone. However, amiodarone can cause hyperthyroidism, which itself can cause cardiac rhythm disturbances or hypothyroidism. This study was done to determine the frequency of recurrent tachycardia in patients with hyperthyroidism caused by amiodarone.

How the study was done. The study subjects were 232 patients with ventricular tachycardia and organic heart disease who were treated with amiodarone. Serum thyroid hormones and thyrotropin were measured, and Holter monitoring was done every 3 months for 2 years or until death or cessation of amiodarone therapy. Recurrent sustained ventricular tachycardia, with or without symptoms, was diagnosed by electrocardiography.

The results of the study. During follow-up 179 patients (77 percent) remained euthyroid, 29 (12 percent) had hyperthyroidism, and 25 (11 percent) had hypothyroidism (1 patient had both). On average, hyperthyroidism was diagnosed 32 months and hypothyroidism 18 months after the start of amiodarone therapy.

Among the 29 patients with hyperthyroidism, the mean heart rate and number of premature contractions per 24 hours were higher when they were hyperthyroid than when they were euthyroid. Nine (31 percent) had recurrence of a sustained tachycardia when they were hyperthyroid and 1 (3 percent) when euthyroid. In contrast, among the 25 patients with hypothyroidism, the mean heart rate and number of ventricular premature contractions per 24 hours were similar when they were hypothyroid and when they were euthyroid; 1 patient (4 percent) each had a sustained tachycardia when hypothyroid and when euthyroid. There were no sudden deaths in either group.

The conclusions of the study. Patients with tachycardia who are treated with amiodarone are more likely to have recurrence of tachycardia if they have hyperthyroidism than if they remain euthyroid.

The original article. Shiga T, Wakaumi M, Matsuda N, Shoda M, Hagiwara N, Sato K, Kasanuki H. Amiodarone-induced thyroid dysfunction and ventricular tachyarrhythmias during long-term therapy in Japan. Jpn Circ J 2001;65:958-60.