The effect of antiarrhythmic drugs on depressed conduction and unidirectional block in sheep Purkinje fibers.

We studied the effect of therapeutic concentrations of lidocaine, procainamide, quinidine, propranolol, and diphenylhydantoin on two models of depressed conduction and unidirectional block produced by asymmetric focal cooling and crushing in sheep Purkinje fibers. All drugs were shown to induce reversible deterioration of conduction. Unidirectional block was converted to bidirectional block with each drug. Improvement of conduction was rare and conversion of unidirectional block to bidirectional conduction never was observed. These experiments suggest that all five drugs may act by a uniform mechanism of action in some reentrant ventricular arrhythmias involving a zone of depressed conduction or unidirectional block within the Purkinje network.