Key result
IV digitoxin prolongs late ventricular repolarization in dogs whereas digoxin has no such effect.
Why the study?
Do digitoxin and digoxin have different effects on right ventricular monophasic action potentials in intact dogs?
Do digitoxin and digoxin have different effects on right ventricular monophasic action potentials in intact dogs?
Digitoxin and digoxin exhibit different late effects on ventricular repolarization in dogs, suggesting potential differences in their antiarrhythmic properties.
Digitoxin's late repolarization effect in dogs warrants caution in extrapolation; leaves open differential antiarrhythmic potential versus digoxin in humans.
The effects of digitoxin and digoxin on right ventricular monophasic action potentials were studied in intact dogs during an 8 hour observation period. Pentobarbital anaesthesia was used, and monophasic action potential recordings were obtained with the suction electrode technique. Intravenous injection of 2.0 mg digitoxin to six dogs, 2.0 mg digoxin to two dogs and 1.0 mg digoxin to five dogs caused a rapid increase in the time taken for 90% repolarisation with return to control values after 20 to 30 min. A late increase in 50 and 90% repolarisation times was observed 2 to 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 to 8 h after the injection) since it reached a maximum towards the end of the observation period. Digitoxin and digoxin thus differed in their late effects on ventricular monophasic action potentials in intact dogs and may possess different antiarrhythmic activity.
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Amlie et al. (1980) studied Intact dogs (animal model) (n=13). Digitoxin and digoxin vs. Baseline control values / each other was evaluated on Right ventricular monophasic action potentials (time taken for 50% and 90% repolarisation). Intravenous digitoxin caused a late increase in 50% and 90% repolarisation times 2 to 4 hours after injection in intact dogs, whereas digoxin had no such late effect.
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