April - June 2006, Volume 2, Issue 2

Trifanescu RA, Fica S, Ursu H, Dimulescu D, Coman I, Ceck C, Barbu C, Coculescu M

Tri-iodothyronine as a risk factor for atrial fibrillation in amiodarone-induced hyperthyroidism

Acta Endo (Buc) 2006, 2 (2): 187-202
doi: 10.4183/aeb.2006.187

Aims: To assess if amiodarone maintains its antiarrhythmic efficacy in the presence of amiodarone-induced hyperthyroidism (AIT) and to identify the tri-iodothyronine (T3) threshold for atrial fibrillation in patients with AIT versus common hyperthyroidism.\r\nPatients and methods. Study group A consists in 49 patients (25 M/24 F) with AIT (220.83 ? 71.33 mg/day along 2.36 ? 2.25 years) and severe cardiopathies (9 valvulopathies, 40 ischaemic, dilatative and hypertensive cardiomyopathies), aged 57.87?12.63 years. Control group B consists in 51 hypothyroid (B1) or euthyroid patients (B2) treated with amiodarone (222.55 ? 68.78 mg/day along 2.67 ? 1.84 years) and also in 100 patients (23M/77F) with overt hyperthyroidism (B3), without major heart diseases, aged 52.74?12.85 years; TSH, total T3, total T4, free T4 were measured by radioimmunoassay. All were clinically, ECG and echocardiography evaluated.\r\nResults. Prevalence of arrhythmias recurrence was 59.2% (29/49 patients) in group A, significantly higher than in each control subgroups B: B1- 28% (7/25), B2- 15.45% (4/26) and B3- 20% (20/100), P< 0.001. Patients from study group A with AIT and T3 levels >250 ng/dL developed significantly more frequent atrial fibrillation (p= 0.04). However, in control group B3 with common hyperthyroidism, no T3 threshold for arrhythmias could be identified. Overall, there were no significant differences in total T3 levels with respect to the presence of atrial fibrillation in both study group A and subgroup B3 with common hyperthyroidism (p=ns).\r\nConclusion. Amiodarone antiarrhythmic efficacy is surpassed in AIT by the increased arrhythmic susceptibility of damaged myocardial tissue to minimally increased thyroid hormones levels. A tri-iodothyronine level > 250 ng/dL superimposed on preexistent proarrhythmic substrate in amiodarone-induced hyperthyroidism should be avoided.

Keywords: amiodarone, hyperthyroidism, tri-iodothyronine threshold, atrial fibrillation, arrhythmias

Correspondence: Raluca Trifanescu, MD, Department of Endocrinology, &#8220;Carol Davila&#8221; University of Medicine and Pharmacy, e-mail: ralucatrifanescu@yahoo.com