Cardiac Effects of a Hypotensive Veratrum Derivative in Dogs Premedicated with Digitalis or Quinidine. ∗

Summary

Veriloid, a reproducible hypotensive derivative of Veratrum viride, was administered in dosage of 1 mcg/kg/minute for 10 minutes to unanesthetized dogs. Similarly the veratrum derivative was administered to unanesthetized dogs premedicated with toxic dosages of digitalis preparations and to others premedicated with toxic dosages of quinidine hydrochloride. The degree of cardiac slowing from the veratrum derivative was found to be a function of pre-existing cardiac rate. No such relation was found for the bradycardia produced by digitalis. Dogs which received digitalis and veratrum showed profound bradycardia. This action appeared to be mediated by increased vagal tone since the slowing was abolished by atropine. Rhythm disturbances due to digitalis were exaggerated by veratrum. A rise in Q-T/R-R ratio above that to be expected by changing cardiac rate was associated with the administration of quinidine hydrochloride. In normal animals and in those which received digitalis, Veriloid or both, the ratio was found to vary as a straight line function of the existing heart rate. Neither quinidine alone at IS or 25 mg/kg nor quinidine and veratrum produced appreciable incidence of arrhythmias. Cardiac slowing was observed in dogs receiving veratrum after the 15 mg/kg dose of quinidine but not after the 25 mg/kg dose.