Key result
In anesthetized dogs, 1.0 mg intravenous digoxin increased dP/dt and decreased heart rate, but unlike 2.0 mg digitoxin, it did not increase atrial refractoriness.
Why the study?
Does digoxin alter inotropic and electrophysiologic parameters differently than digitoxin in intact dogs?
Does digoxin alter inotropic and electrophysiologic parameters differently than digitoxin in intact dogs?
Digoxin and digitoxin exhibit different electrophysiological profiles in intact dogs, with digitoxin having more pronounced late effects on heart rate and AV nodal conduction.
ABSTRACT we wanted to study changes in the inotropic and electrophysiologic effects of digoxin after a single dose and to correlate them to serum digoxin concentrations. Furthermore we wanted to compare data obtained in the present study to results obtained in a similar study after digitoxin. Six pentobarbital anaesthetised Labrador dogs were given 1.0 mg digoxin intravenously. Left heart catheterization and His bundle recordings were performed. Pacing and programmed electrical stimulation were used to determine heart rate independant changes in dP/dt, intra‐atrial, AV‐nodal, His‐Purkinje and intraventricular conduction times. The effective (A‐ERP) and the functional (A‐FRP) refractory periods of the atrium, the functional refractory period of the AV node (AV‐FRP) were measured. Serum digoxin concentrations were determined with radio‐immu‐noassay. Median serum digoxin half‐time (T/2) was 4.2 hours. dP/dt increased after digoxin with maximum values after 1 1/2 hour. Digoxin concentrations correlated linearly with inotropic response. Heart rate fell significantly within 2 minutes and remain below control values for 3 hours concomitant with an increase in A‐H time and AV‐FRP. A‐ERP and A‐FRP did not change. A significant positive correlation was observed between decrease in AV‐FRP and serum concentrations in the elimination phase, while no obvious relationship existed between the other electrophysiological variables measured and serum concentrations. Digoxin and digitoxin differed in their electrophysiological effects. while digitoxin increased atrial refractoriness, no effect was observed after digoxin. Digitoxin (2.0 mg) caused more pronounced late effect on heart rate and AV nodal conduction and refractoriness than digoxin (1.0 mg).
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Amlie et al. (1981) studied this question. Digoxin vs. Digitoxin (2.0 mg) was evaluated on Inotropic and electrophysiologic effects and correlation to serum digoxin concentrations. In anesthetized dogs, 1.0 mg intravenous digoxin increased dP/dt and decreased heart rate, but unlike 2.0 mg digitoxin, it did not increase atrial refractoriness.
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