Re-entrant ventricular arrhythmias in the late myocardial infarction period. 4. Mechanism of action of lidocaine.

The effect of lidocaine on re-entrant ventricular arrhythmias (RVA) was studied in dogs 3-7 days following ligation of the anterior descending coronary artery; direct recordings were made of the re-entrant pathway (RP) from the epicardial surface of the infarction zone (IZ). Lidocaine in a therapeutic dose consistently prolonged refractoriness of potentially RP(s) in the IZ and produced a higher degree of conduction block at a constant heart rate. Conduction in the adjacent normal zone was not affected. The impairment of conduction induced by lidocaine in the RP was directly related to its ability to abolish re-entrant ventricular beats and tachycardia. Gradual slowing of conduction in the RP consistently developed before abolition: lengthening of coupling of extrasystolic beats in surface leads and gradual slowing of ventricular tachycardia rate occurred. The termination of re-entry was characteristically associated with complete block in the RP. A "selectivity hypothesis" for the antiarrhythmic action of lidocaine is proposed.