Effects of intravenous amiodarone in patients with inducible repetitive ventricular responses and ventricular tachycardia

We studied the effects of intravenous amiodarone administration (5 mg/kg) on reproducible repetitive ventricular responses and ventricular tachycardia (VT) induced by programmed electrical stimulation of the heart in 32 patients. Intravenous amiodarone prevented induction of bundle branch reentry in only 2 of 11 patients (18.2%) and did not change His-Purkinje conduction and refractoriness in the remaining 9 of 11 (81.8%) patients. In contrast to the small effect of intravenous amiodarone on bundle branch reentry, the drug completely abolished intraventricular reentry in three of nine (33.3%) patients and in the remaining six of nine (66.7%) patients decreased the number of intraventricular reentrant beats from up to five beats in control to one to two beats after the drug. The drug also prevented induction of VT (≥5 ventricular ectopic beats in a row) in three of five (60%) patients with nonsustained VT and in three of seven (42.9%) patients with sustained VT. In two of seven (28.6%) patients with sustained VT, only nonsustained tachycardia could be induced after drug administration. In another two of seven (28.6%) patients, sustained VT with slower rates was induced after the drug. In 11 of 12 (91.7%) patients with VT the coupling interval between the last stimulus and the first ventricular beat increased after drug administration. These effects of intravenous amiodarone occurred in the absence of effect on ventricular effective refractory period. These findings suggest that intravenous amiodarone might have greater effect on diseased ventricular tissue, the site of reentry in VT, than on healthy ventricular tissue.