PROSPECTIVE, RANDOMIZED COMPARISON OF CONVENTIONAL AND HIGH-DOSE LOADING REGIMENS OF AMIODARONE IN THE TREATMENT OF VENTRICULAR-TACHYCARDIA

Objectives. The purpose of this prospective randomized study was to co mpare the electrophysiologic effects of conventional and high dose loa ding regimens of amiodarone in patients with sustained ventricular tac hycardia. Background. Uncontrolled studies in which patients have been treated with an oral loading dose of 2 to 4 g/day of amiodarone have suggested that, compared with a conventional loading dose, this dosing regimen results in more rapid control of spontaneous ventricular tach ycardia and ventricular tachycardia induced by programmed stimulation. Methods. Patients in whom sustained monomorphic ventricular tachycard ia was inducible by programmed stimulation and who were refractory to class I antiarrhythmic medications were randomly assigned to receive e ither a conventional (n = 15) or a high (n = 17) loading dose of amiod arone. The conventional dose consisted of 600 mg twice a day for 10 da ys. The high dose regimen consisted of 50 mg/kg body weight per day on days 1 to 3, 30 mg/kg per day on days 4 and 5 and 600 mg twice a day on days 6 to 10. An electrophysiologic test was performed in the basel ine state and after 3 and 10 days of therapy. An adequate response to amiodarone was defined as the inability to induce ventricular tachycar dia or the ability to induce only relatively slow (cycle length greate r than or equal to 350 ms) hemodynamically stable ventricular tachycar dia. Results. After 3 days of therapy, 2 of 14 patients who received t he conventional loading dose and 6 of 15 patients who received the hig h dose loading regimen had an adequate response to amiodarone (p = 0.0 8). After 10 days of therapy, four patients in each group had an adequ ate response to amiodarone (p = NS). Three patients who received the h igh dose and one patient who received the conventional dose of amiodar one had an adequate response after 3 days of therapy but not after 10 days of therapy. There were significant increases in the sinus cycle l ength, atrioventricular block cycle length, ventricular effective refr actory period and ventricular tachycardia cycle length after 3 and 10 days of therapy compared with baseline values regardless of the dosing regimen. The extent of the effects of amiodarone on these variables a fter 3 and 10 days of therapy was similar with both dosing regimens. C onclusions. The therapeutic and electrophysiologic effects of conventi onal and high dose loading regimens of amiodarone do not differ signif icantly after 3 or 10 days of therapy. High oral loading doses of amio darone do not offer any significant clinical advantage over a conventi onal loading dose of amiodarone for controlling ventricular tachycardi a induced by programmed stimulation.