[Tetrodotoxin potentiation of the antiarrhythmic action of lidocaine in the late stage of experimental myocardial infarct].

Lidocaine (4--12 mg/kg) and the specific fast sodium current blocker tetrodotoxin (TTX) (1--6 mg/kg, i. v.) reduced ventricular arrhythmias that occurred 24 h after coronary artery ligation in dogs. Infusion of a mixture of subthreshold doses of lidocaine and TTX decreased ventricular arrhythmias to the same degree as infusion of threshold doses of either agent alone. This finding suggests that the antiarrhythmic action of lidocaine in the late stage of myocardial infarction is due to inhibition of the fast inward, sodium current. The possible mechanisms of rhythm disturbances in the late stage of myocardial infarction are discussed.