Effects of altered heart rate on chloroformepinephrine cardiac arrhythmia.

• It was reported recently that cardiac arrhythmia induced in cyclopropane anesthetized dogs by infusion of epinephrine could be converted to normal sinus rhythm by vagal stimulation. The termination of multifocal ventricular tachycardia is interesting because it is not readily apparent how vagal influence, presumably limited to the A-V node or upper bundle of His, alters arrhythmia predominantly of ventricular origin. In exploratory studies designed to confirm the effects of vagal stimulation on ventricular arrhythmia in dogs anesthetized by chloroform, it was observed that when conversion to a supraventricular rhythm occurred it was invariably after slowing of the heart rate, i.e., rate as well as rhythm was changed in the conversion. This indication that decreased heart rate might be important in the conversion to sinus rhythm suggested that the frequency of ventricular excitation is a factor in the genesis of the arrhythmia. The data reported in this communication comprise a test and an apparent confirmation of that hypothesis.