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.
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