Effects of lidocaine on conduction of extrasystoles in the normal canine heart

The effect of lidocaine on the conduction of extrasystoles was studied in 8 open-chest dogs after atrioventricular nodal block. Simultaneous recording of endocardial and epicardial activation provided separate measures of endocardial (Purkinje) conduction as well as myocardial (muscle) conduction. Lidocaine (1.25-10.0 mg/kg) caused a dose-dependent slowing of conduction of midrange extrasystoles (250-400 ms) in both the Purkinje system and the myocardium, which became statistically significant at doses larger than 1.25 mg/kg. On the other hand, low doses of lidocaine caused speeding of early extrasystoles, i.e., coupling intervals (<250 ms) in the Purkinje system but not in the myocardium. Measurement of transmural conduction time as a function of coupling interval revealed a period of “apparent“ supernormal conduction through ventricular muscle that was eliminated at high doses of lidocaine.