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Amiodarone-Induced Thyrotoxicosis Is a Predictor of Adverse Cardiovascular Outcome

Division of Cardiology (K.-H.Y., C.-W.S., C.-H.L., M.Y., M.M., Y.-F.S., H.-F.T.), Department of Medicine, Queen Mary Hospital, University of Hong Kong, Hong Kong; and Cardiac Medical Unit (M.-H.J., K.F., W.-H.C.), Grantham Hospital, Hong Kong

Address all correspondence and requests for reprints to: Dr. Wing-Hing Chow, Cardiac Medical Unit, Grantham Hospital, Hong Kong. E-mail: chowwh{at}ha.org.hk.

Background: Amiodarone-induced thyrotoxicosis (AIT) is a clinical condition that is notoriously difficult to manage; the relative risk of adverse cardiovascular events in these patients compared with euthyroid patients is largely unknown.

Objective: We compared the clinical characteristics and major adverse cardiovascular events (MACE) in AIT and euthyroid patients.

Method: Patients at a tertiary referral center who had been prescribed amiodarone for at least 3 months were retrospectively analyzed. Baseline clinical characteristics, laboratory parameters, and outcome events were evaluated. MACE was defined as cardiovascular mortality, myocardial infarction, stroke and heart failure, or ventricular arrhythmias that required hospitalization.

Results: A total of 354 patients (61.8 ± 14.1 yr; 64.7% male) with a mean follow-up of 48.6 ± 26.7 months were studied. AIT, euthyroid status, and amiodarone-induced hypothyroidism were identified in 57 (16.1%), 224 (63.3%), and 73 (20.6%) patients, respectively. No differences in baseline clinical characteristics were observed between AIT and euthyroid patients. Nonetheless AIT patients demonstrated a higher MACE rate (31.6 vs. 10.7%, P < 0.01), mostly driven by a higher rate of ventricular arrhythmias that required admission (7.0 vs. 1.3%, P = 0.03). Cox-regression multivariate analysis revealed that AIT (hazard ratio 2.68; confidence interval 1.53–4.68; P < 0.01) and left ventricular ejection fraction less than 45% (hazard ratio 2.52; confidence interval 1.43–4.42; P < 0.01) were independent predictors of MACE.

Conclusion: In patients prescribed long-term amiodarone therapy, occurrence of AIT is associated with a 2.7-fold increased risk of MACE. Regular and close biochemical surveillance is thus advisable to identify and treat this high-risk group of patients.