THE ACTION OF QUINIDINE ON THE HEART IN THE NORMAL UNANESTHETIZED DOG

¹ Department of Pharmacology, Cornell University Medical College, New York City

1. The effect of intravenous injections of quinidine in therapeutic and toxic doses on the heart of the normal unanesthetized dog was studied electrocardiographically.

2. In both therapeutic and convulsive doses, quinidine does not produce slowing but acceleration of the sinus rate. Acceleration occurs in vagotomized dogs as well, especially in those cases in which the vagotomy does not result in an extremely rapid heart rate.

3. In doses up to those causing convulsions, quinidine does not produce any prolongation of A-V conduction. Frequently the P-R interval is shortened, simultaneously with the sinus acceleration.

4. Quinidine causes prolongation of intraventricular conduction (increased QRS time). This is sometimes in evidence with therapeutic doses but is most constant and pronounced after larger doses.

5. A negative T-wave becomes positive and a positive T-wave increases in amplitude. This effect of quinidine is constant in normal dogs and is a very sensitive reaction, occurring after doses as small as 2 mgm., and may appear without any other changes in the electrocardiogram.

6. All of the above effects are fleeting, coming on frequently within less than a minute after the injection and disappearing in many cases in less than fifteen minutes.

7. Our results are in some respects at variance with those reported in the literature. It is suggested that anesthesia and various operative procedures used in most of the previous studies on animals may be chiefly responsible for the differences.