Ventricular Excitability in the Unanesthetized Dog and Its Modification by Pentobarbital Anesthesia

¹ From the Department of Physiology, Boston University School of Medicine, Boston, Massachusetts

Cardiac excitability and refractoriness were determined in the unanesthetized dog via intrajugular electrodes in one group, and chronically implanted electrodes in another. The TRP in such dogs averaged 39% of the driving cycle, the FRP 42% and the ARP 32%. The intraperitoneal administration of pentobarbital resulted in small but consistent increments in these parameters, the TRP in anesthetized animals averaging 49% of the cycle, the FRP 52% and the ARP 40%. The diastolic threshold and RRP were unaltered. It is apparent that in ventricular excitability studies conducted under pentobarbital anesthesia there occur small but consistent modifications of the refractory period, cognizance of which should be taken when evaluating data obtained under these conditions.