An easy and direct approach to investigate conduction properties of the rabbit sinus node

The sinus node is not only important for the generation of the cardiac impulse but also as conductor of this impulse from the site of origin toward the atrium. An easy method to investigate conduction properties of sinus nodal tissue directly is described. The isolated right atrium of the rabbit was divided--via an incision perpendicular to the crista terminalis--into two halves connected only by a bridge of sinus nodal tissue. By means of two atrial surface electrodes conduction through the sinus node bridge was monitored. It appeared that conduction in the sino-atrial border zone is many times slower than in the atrium and refractory period markedly longer. In the center of the sinus node conduction is again slower and refractory period longer than in the border zone. Validity of the method was tested by reconstruction of the conduction route of stimulated impulses using microelectrode recordings. Applications of the method were demonstrated by studying the effects of rate and rhythm, hypothermia, hypoxia, acetylcholine and norepinephrine as well as verapamil. The model is suitable for investigation of the effects of drugs and other interventions on impulse conduction in sinus nodal tissue.