Electrophysiological actions of flecainide in normal and infarcted canine Purkinje fibers.

The electrophysiological effects of flecainide, 0.1, 0.5 and 1.0 mg/l, on action potential characteristics were examined in normal Purkinje fibers and Purkinje fibers surviving infarction, at stimulation cycle lengths of 1000 and 300 ms. Overshoot, amplitude and dV/dtmax were reduced significantly in a dose-dependent manner by flecainide in both normal Purkinje fibers and Purkinje fibers surviving infarction. Action potential duration was shortened by flecainide to a greater extent: at the cycle length of 1000 ms compared to 300 ms; at 50% repolarization compared to 90%; and in normal preparations compared to infarcted preparations. Activation time was increased by flecainide in a dose-dependent manner in both types of preparations. This effect was enhanced at the shorter cycle length. In both normal and infarcted preparations, flecainide shortened the ERP of those having a longer initial ERP and lengthened those with a shorter ERP. This effect was significant only at the stimulation cycle length of 1000 ms. This study indicates that flecainide has properties unique and different from traditional antiarrhythmic drugs.