THE EFFECT OF QUINIDINE ON ARRHYTHMIAS INDUCED BY CYCLOPROPANE AND CYCLOPROPANE-EPINEPHRINE

Abstract

In medium sized dogs premedicated with 200 mg./kg. barbital-Na intraperit., the common carotid artery was cannulated and blood pressure tracings recorded on moving photographic paper with a Hamilton optical manometer, and ecg. tracings were obtained with a direct writing instrument. Cyclopropane-O2 mixtures were administered using CO2 absorption technic through a cuffed endotracheal tube. In the control series 6 dogs were anesthetized by cyclopropane and were given 0.02 mg./kg- of epinephrine intraven. Only 1 survived the 1st admn. of epinephrine and died when it was repeated 15 min. later. In a 2d series, 1 mg./kg. of quinidine was given after the induction of anesthesia. Two dogs developed ventricular fibrillation when epinephrine was given 12 min. after quinidine; 5 dogs were completely protected when the interval between the quinidine and epinephrine admns. was less than 10 min. When epinephrine was repeated, 2 of these developed ventricular fibrillation, and 3 were protected. One dog showed no arrhythmia after 3 subsequent admns. within 65 min. Of 6 dogs receiving 5 mg./kg. of quinidine, 4 showed no arrhythmia when epinephrine was given within 5 min., 2 demonstrated prefibrillary changes when epinephrine was given after 10 min. When epinephrine was given within 17-22 min. to the previously protected dogs, 1 showed minor prefibrillary changes, and 3 developed ventricular fibrillation. In the 4th series, 4 dogs received 10 mg./kg. of quinidine. When epinephrine was given within 10 min., only 1 developed ventricular arrhythmias of 4 sec. duration. On subsequent epinephrine admn., the same dog and 1 other dog developed ventricular fibrillation, while 2 showed no arrhythmias. In a 5th series, 3 dogs received 20 mg./kg. of quinidine and were completely protected from arrhythmias if epinephrine was given within 8 min. On subsequent epinephrine admns., 1 showed no arrhythmia and 2 showed transient prefibrillary changes. The effects of quinidine sulfate and quinidine lactate were identical. Both pulse rate and blood pressure tended to decrease after quinidine admn. The protective action of quinidine began within 30 sec. after its intraven. admn. After 10 min., the duration of the protective action tended to vary directly with the dose, lasting for an avg. period of 24.3 min. with 1 and 5 mg./kg., and 1-3 hr. with 20 mg./kg. doses.