THE ACTION OF PAPAVERINE ON THE HEART OF THE DOG

¹ From the Cardiovascular Department, Michael Reese Hospital, Chicago

1. Papaverine depresses or annuls the responsiveness of the auricles to faradic stimulation.

2. In small doses it may augment A-V conductivity, but in larger doses it depresses A-V conductivity leading to partial or complete A-V block. Larger doses also cause intraventricular block.

3. It diminishes the irritability of the auricles and ventricles to extrinsic stimuli and prolongs the refractory period of the ventricles and auricles.

4. In the anesthetized dog breathing naturally and with natural beating of the heart, small doses of papaverine usually cause temporary sinus tachycardia. Larger doses lead to sinus slowing or standstill sometimes with nodal escapes or nodal rhythm, active ectopic ventricular rhythms and even ventricular flutter and fibrillation. Death with toxic doses is due to cardiac or ventricular standstill or to terminal ventricular fibrillation of a peculiar type.

5. The favorable action of this drug in reversing artificially induced ventricular fibrillation, and in diminishing or abrogating ventricular premature contractions electrically induced, is explained as due to a depression of conductivity and irritability and to a prolongation of the refractory period of the ventricles.

6. Evidence is presented to show that these are primarily direct effects on the heart.

7. The possible prophylactic and therapeutic clinical application of papaverine hydrochloride in the management of ectopic rhythms and ventricular fibrillation is suggested, but caution is advised inasmuch as this drug may cause the very arrhythmias for which it may be recommended.

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