ACTIONS OF LIDOCAINE ON REENTRANT VENTRICULAR RHYTHMS IN THE SUBACUTEMYOCARDIAL-INFARCTION PERIOD IN DOGS

The actions of lidocaine were studied in 18 dogs, 4 days after ligatio n of the left anterior descending artery, by computerized mapping. Lid ocaine only occasionally suppressed the induction of reentry. At fast heart rates, lidocaine actually facilitated the induction of reentry. The effects on conduction and refractoriness of normal and ischemic my ocardium were measured using high-resolution techniques. Lidocaine pro moted reentry by a rate-dependent increase in refractory gradient, res ulting in additional block, and a selective decrease in conduction vel ocity in ischemic tissue, resulting in additional conduction delay. Li docaine could prevent reentry through a rate-independent differential, increase in refractory period gradient at the entrance to the common pathway of the circuit, causing block of the reentrant impulse. We con clude that the proarrhythmic effect of lidocaine is due to increased c onduction delay and block while the antiarrhythmic effect is due to bl ock of the reentrant impulse by prolonged refractoriness in the common pathway.