Effect of digoxin on sinus nodal reentry in the dog

The effect of digoxin on sinus reentry was examined in 20 open chest mongrel dogs during infusion of digoxin at a rate of 2.5 mu g/kg per min. The extrinsic cardiac nerve supply was removed acutely in 10 dogs and was left intact in the remaining 10 dogs. Sinus nodal reentry was relatively unaffected by digoxin in 18 of 20 dogs. In these 18 dogs, digitalis toxicity developed before reentry was abolished and was manifested as increased atrial and ventricular automaticity in 14 and as advanced atrioventricular (A-V) block in four. In the remaining two dogs, sinus nodal reentry was relatively sensitive to digoxin and was abolished before toxicity became manifest as advanced A-V block. The knowledge of the relative insensitivity of sinus nodal reentry to digoxin, at least in this experimental model, contrasts with the previously reported sensitivity of sinus nodal reentry to quinidine, and may be important in the management of sinus nodal reentry in man.