[Transposition of the pacemaker in the right atrium during stimulation of the vagus nerve in the dog].

The heart rate and intraatrial latencies between epicardial electrograms from three sites of the right atrium have been studied during vagal stimulation in open-chest dogs. It has been shown that alterations of latencies started at a certain cardiac cycle length irrespective of pacing frequency. A transitional process of changes from a steady latency value in the control to another steady value during vagal stimulation has been observed. The transitional process has been simulated in experimental procedure in which two sites of the right atrium were paced at close and constant frequencies. To interpret the results obtained one-dimensional model of the sinus node has been constructed. According to the model, pacemaker shift within the sinus node results from a competition between two foci of automaticity with close intrinsic frequencies.