Electrophysiological effects of dridocainide on isolated canine, guinea-pig and human cardiac tissues

The cellular electrophysiological effects of dridocainide (EGIS-3966), a novel class I antiarrhythmic agent, was studied using conventional microelectrode techniques in canine cardiac Purkinje fibres and papillary muscle preparations obtained from humans and guinea-pigs. In each preparation, dridocainide (0.6-2 mumol/l) decreased the maximum velocity of action potential upstroke (Vmax) in a frequency-dependent manner, although marked differences were observed in its effects in Purkinje fibre and ventricular muscle preparations. In canine Purkinje fibres, action potential duration measured at 50% and 90% of repolarization was decreased, while action potential duration measured at 10% of repolarization was increased by dridocainide. In addition, the plateau of the action potential was depressed by the drug. These changes in action potential configuration were not observed in guinea pig or human papillary muscles. The offset kinetics of the dridocainide-induced Vmax block were different in Purkinje fibres and in ventricular muscle: the slow time constant of recovery of Vmax was estimated to be 2.5 s in dog Purkinje fibre and 5-6 s in human and guinea-pig papillary muscle. In guinea-pig papillary muscle, the rate of onset of the Vmax block was 0.15 and 0.2 per action potential in the presence of 0.6 and 2 mumol/l dridocainide, respectively. Dridocainide also decreased the force of contraction in this preparation. On the basis of the present results, dridocainide appears to possess mixed class I.C and I.A properties, with I.C predominance in human and guinea-pig ventricular muscle. Present results also indicate that results of conventional classification of class I drugs may depend on the parameters chosen, as well as on the preparation selected.