CARDIAC PACEMAKER - EFFECTS OF REGULARLY SPACED NERVOUS INPUT

Experiments were conducted to see if the observations reported by Perkel and associates could be extended to the cardiac pacemaker. In anesthetized cats and rats, the pacemaker responded to regularly spaced vagal stimuli in simple frequency ratios over appreciable ranges of frequency; within these ranges, increase in vagal frequency caused increase in pacemaker rate. Between the ranges, response was orthodox. Vagal or sympathetic decentralization extended stable zones, reserpine pretreatment reduced them. The point in the electrocardiographic cycle at which the stimulus fell during a period of fixed ratio changed predictably. This change accorded with and is explained by the effect of individual stimuli, arriving at different times in relation to the P wave, on the sinus pacemaking rate. Fixed ratios, but no ranges, were demonstrated with sympathetic stimulation. Dual innervation may serve to prevent paradoxical responses, and monitoring of pacemaking may play a physiologic part in determining frequency in nerves controlling the pacemaker. © 1969.