Retrograde conduction and isorhythmic dissociation in heart block

In a case of heart block with retrograde conduction a catheter electrode was introduced to pace the ventricles. Under these circumstances a planned study was undertaken. The results indicate: (1) Alterations in rate of the stimulus pacemaker, in a narrow range around the natural rate of the sinoauricular node, influence the rate of the latter to follow the induced changes in the artificial stimulus. (2) Continuing retrograde conduction to the auricle can occur when the sinus node is suppressed by raising the rate of the stimulus pacemaker. (3) Continuing retrograde conduction to the auricle can occur with long series of fusion P waves in the auricle. It is concluded that retrograde conduction to the auricle is not dependent on a supernormal-phase phenomenon.