The effect of quinidine on interauricular conduction and irritability in the terrapin's heart.

Abstract

Numerous investigators have demonstrated that quinidine decreases the irritability of the heart muscle and the auriculo ventricular conduction. We have recorded the contractions of both auricles in the terrapin, and find that, although much stronger stimuli (rhythmic make-and-break shocks) are required to cause extrasystolic responses after intraventricular injections of 1-2 mg. quinidine sulphate than before, there is no marked disturbance of conduction of spontaneous contractions or of rapid rhythmic extrasystoles from right auricle to left auricle. This indicates that quinidine depresses irritability more than it depresses intrand inter-auricular conductivity; and renders it probable that in auricular fibrillation it rather suppresses the genesis of ectopic impulses than that it blocks the conduction of circus movements when once generated. Our results are in accord with the investigations of Hirschfelder in 1908, which indicated that increased irritability of the heart muscle is one of the important factors in the genesis of auricular fibrillation.