Electrophysiological effects of lidocaine, l-chlorpheniramine, and bepridil on normal and ouabain-intoxicated canine Purkinje fibers.

We compared the electrophysiological effects of lidocaine, l-chlorpheniramine, and bepridil on both normal and ouabain-induced automaticity of canine Purkinje fibers. All three drugs suppressed the automaticity of spontaneously beating Purkinje fibers, but only lidocaine and bepridil reduced the amplitude of delayed afterdepolarizations induced by ouabain. Whereas lidocaine caused equal decreases in delayed afterdepolarization amplitude initiated at cycle lengths of stimulation between 1,000 and 250 ms, bepridil reduced their amplitude more at short than at long cycle lengths. Similarly, bepridil's but not lidocaine's effects on action potential characteristics were also dependent on the cycle length of stimulation; more marked decreases in amplitude and rate of rise of the action potential being observed at short cycle lengths. Lidocaine, alone, also markedly prolonged the period of overdrive suppression.