Comparative electrophysiologic effects of digoxin in the nonsedated chronically instrumented puppy

The electrophysiologic effects of acute but not chronic administration of cardiac glycosides have been studied. Nineteen chronically instrumented beagle puppies underwent 2-week courses of parenteral digoxin in three dosage regimens: six received digoxin, 0.04 mg/kg/day; seven received 0.03 mg/kg/day; and 11 received 0.02 mg/kg/day. Mean serum concentrations were 3.2 ng/ml, 1.3 ng/ml, and 1.0 ng/ml, respectively. Significant electrophysiologic effects on sinus node function were produced only by the highest dose. Atrioventricular node conduction was significantly delayed among animals receiving both high and middle dosages. All three regimens significantly effected atrioventricular specialized conduction system functional refractory periods. Atropine decreased digoxin-induced effects on all measured parameters but totally eliminated the digoxin effect on the corrected sinus node recovery time.