Digoxin- and digitoxin-induced changes in monophasic action potential of the right ventricle of the dog heart

Abstract

The effects of digitoxin and digoxin on right ventricular monophasic action potentials were studied in intact dogs during an 8 h observation period. Pentobarbital anesthesia was used and monophasic action potential recordings were obtained with the suction electrode technique. I.v. injection of 2.0 mg digitoxin to 6 dogs, 2.0 mg digoxin to 2 dogs and 1.0 mg digoxin to 5 dogs caused a rapid increase in the time taken for 90% repolarization with return to control values after 20-30 min. A late increase in 50 and 90% repolarization times was observed 2-4 h after digitoxin while digoxin had no such effect. The late action potential prolonging effect was inversely correlated to serum concentrations in the early elimination phase (2-8 h after the injection) since it reached a maximum towards the end of the observation period. Digitoxin and digoxin differed in their late effects on ventricular monophasic action potentials in intact dogs and may possess different antiarrhythmic activity.