Interrelationships between serum levels of amiodarone, desethylamiodarone, reverse T3 and the QT interval during long-term amiodarone treatment

Abstract

The interrelationships between serum levels of amiodarone, desethylamiodarone, and reverse T3, and changes in the corrected QT interval ([Delta]QTc) were examined in 22 patients during long-term treatment with amiodarone. At 1, 3, and 6 months of follow-up, the correlation coefficient between serum levels of amiodarone or desethylamiodarone and reverse T3 ranged from 0.01 to -0.2 (p > 0.4). At the same time intervals, the correlation coefficient between both amiodarone and desethylamiodarone levels and [Delta]QTc ranged from 0.1 to -0.1 (p > 0.6), and the correlation coefficient between reverse T3 and [Delta]QTc also ranged between 0.1 to -0.1 (p> 0.5). Substituting percent [Delta]QTc for [Delta]QTc also did not reveal a significant correlation. These data demonstrate that serum levels of reverse T3 cannot be used as a substitute for serum levels of amiodarone in monitoring patients being treated with amiodarone. The absence of a correlation between serum reverse T3 levels and [Delta]QTc suggests that the delay in repolarization which occurs during amiodarone therapy is not secondary to an amiodarone-induced abnormality in thyroid hormone metabolism.