RC1.5 - ECE_1492 - Patterns of amiodarone-related thyroid dysfunction and associated comorbidities: a nationwide study

Introduction Amiodarone is the most commonly used antiarrhythmic medication in the Western world, with a multifaceted mechanism of action. It is highly effective in treating and preventing both atrial and ventricular tachyarrhythmias. Despite its efficacy, amiodarone use is associated with significant side effects, including thyroid dysfunction, pulmonary fibrosis, hepatic impairment, and cardiac rhythm disturbances. Objective This study evaluated amiodarone-induced thyroid dysfunction (AITD) in previously euthyroid individuals and assessed associated cardiovascular risks. Methods A retrospective cohort of patients prescribed amiodarone from 2010 to 2022 was studied. Patients with a history of thyroid disease were excluded. Eligible participants with normal TSH levels were included. Patients were followed for up to 5 years and categorized into four groups based on TSH levels: euthyroid (0.5 < TSH < 4.5), amiodarone-induced hypothyroidism (AIH; TSH > 10), subclinical AIH (4.5 < TSH < 10), and amiodarone-induced thyrotoxicosis (AIT; TSH <). The AIT group was further subdivided into two groups: those with TSH < 0.1 and those with subclinical AIT (0.1 < TSH < 0.5). Outcomes included mortality, heart failure (HF), acute coronary syndrome (ACS), atrial fibrillation (AF), and ischemic stroke (IS). Results Of 43 880 records, 13 444 patients met the inclusion criteria (mean age: 73.8 ± 10.7 years; 55.9% male). During follow-up, 65.6% maintained normal TSH, 23.4% developed subclinical AIH, 7.1% developed AIH, and 3.8% developed AIT; 1.8% had subclinical AIT and 2.1% had AIT. AIH patients were older than previously reported. AIT patients were younger (71.3 ± 10.9 years) and predominantly male. AIT was associated with a higher risk of mortality (OR = 1.64; 95% CI, 1.24-2.17), particularly in the subclinical group. An increased risk of HF was observed in both AIH (OR 1.61, 95% CI 1.23-2.12) and subclinical AIH (OR 1.3, 95% CI 1.11-1.51). Conclusions This extensive study underscores the importance of risk assessment and management in patients receiving amiodarone. The average age of patients who developed thyroid disorders was higher than previously reported, particularly among those with hypothyroidism. The study emphasizes the need for vigilance not only in symptomatic patients with overt thyroid dysfunction but also in those with subclinical hypo- and hyperthyroidism. Although the drug remains a key treatment for arrhythmias, its potential complications, particularly thyroid dysfunction and associated cardiovascular risks, require frequent monitoring for early detection. Further research is needed to explore strategies that balance the therapeutic benefits of amiodarone against its risks and to evaluate appropriate alternative treatment modalities.