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Amiodarone-induced thyrotoxicosis linked to increased risk for major adverse cardiac events
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Patients with amiodarone-induced thyrotoxicosis had a 2.7-fold increased risk for adverse cardiovascular outcomes.
Based on this finding, regular biochemical surveillance is advisable for patients with amiodarone-induced thyrotoxicosis, according to researchers from Hong Kong.
The study was designed to compare the clinical characteristics and major adverse cardiac events in euthyroid patients and patients with amiodarone-induced thyrotoxicosis. The researchers enrolled 354 patients who had received amiodarone for at least three months and followed them for a mean of 48.6 months. Major adverse cardiac events were classified as cardiovascular-related mortality, myocardial infarction, stroke and heart failure or ventricular arrhythmias in which hospitalization was necessary, according to the abstract.
Fifty-seven (16.1%) of the 354 patients had amiodarone-induced thyrotoxicosis; 224 (63.3%) were euthyroid and 73 (20.6%) had amiodarone-induced hypothyroidism. The researchers reported no difference in clinical characteristics between amiodarone-induced thyrotoxicosis and euthyroid patients at baseline.
Patients with amiodarone-induced thyrotoxicosis had a higher rate of major adverse cardiac events compared with euthyroid patients (31.6% vs. 10.7%; P<.01). The researchers said this finding was driven by a higher rate of ventricular arrhythmias that required hospital admission (7% vs. 1.3%; P=.03).
Amiodarone-induced thyrotoxicosis (HR=2.68; P<.01) and left ventricular ejection fraction <45% (HR=2.52; P<.01) were independent predictors of major adverse cardiac events, according to multivariate analysis results. – by Katie Kalvaitis
J Clin Endocrinol Metab. 2008;doi:10.1210/jc.2008-1907.
Results of this retrospective study showed a significant increase in major adverse cardiac events in patients with amiodarone-induced thyrotoxicosis compared with those receiving amiodarone who were hypothyroid or euthyroid. Ventricular arrhythmia was the most common adverse cardiac event, which can be linked to an effect of excess thyroid hormone. The adverse cardiac events occurred relatively early in the course of amiodarone-induced thyrotoxicosis. Although not directly assessed in this study, these findings would suggest that early diagnosis and treatment of thyrotoxicosis should be pursued in these patients. Effective treatment of amiodarone-induced thyrotoxicosis, however, is often challenging. The influence of treatment of amiodarone-induced thyrotoxicosis on the adverse cardiac events will need to be studied. The finding that patients with diagnosed and treated amiodarone-induced hypothyroidism did not have an increase in adverse cardiac events is reassuring for management of these patients.
– Gregory A. Brent, MD
Endocrine Today Editorial Board member