Serum reverse T3 and amiodarone efficacy

The use of serum reverse T3 (rT3) levels in the assessment of amiodarone efficacy is controversial. We prospectively studied 10 patients with frequent ventricular ectopy and symptomatic ventricular tachycardia (VT) treated with amiodarone. Serial 24-h Holter monitor, thyroid function studies including serum rT3, and 12-lead electrocardiogram were performed on each patient at baseline, and at 1, 4, 12, and 24 weeks of oral amiodarone therapy. Serial Holter monitors on therapy were analyzed for 100% suppression of VT, 90% suppression of couplets, and 85% suppression of ventricular ectopic beats (VEBs) compared with baseline Holter, defining patient groups VT-, Co-, and VEB-, respectively. Lack of arrhythmia suppression to this degree defined groups as VT+, Co+, and VEB+. There were no statistically significant differences in rT3 levels between VT+ and VT- groups, Co+ and Co- groups, or the VEB+ and VEB- groups. VT suppression could not be predicted at any rT3 level. We conclude that serum rT3 is an insensitive means of assessing amiodarone efficacy.