Electrophysiologic effects of mexiletine on normal and ischemic ventricles.
The effects of mexiletine on ventricular electrophysiologic properties were studied in seven normal and ten ischemic canine ventricles. Ventricular fibrillation threshold was significantly increased and idioventricular automaticity was significantly suppressed after intravenous administration of 2 mg/kg of mexiletine. Diastolic threshold, effective refractory period and ventricular conduction time were all increased slightly after the drug administration, although the changes were not statistically significant. Rapidly repetitive responses and/or fibrillation were induced in the ischemic ventricle by two early premature beats in six of ten dogs, but these serious arrhythmias could be induced in none of the ten dogs after mexiletine pretreatment. The study indicates that the mode of action of mexiletine is similar to that of lidocaine and the drug is an effective antiarrhythmic agent in preventing ventricular arrhythmias in dog ventricles during myocardial ischemia.