Auriculo-ventricular Rhythm.

assumes control over the ventricles. When this happens, two types of auriculo-ventricular rhythm may arise. One is called A-V nodal rhythm and is recognized by the inverted P waves, which are as a rule either abnormally close to the QRS complex or may follow it. The second type of auriculo-ventricular rhythm is known as A-V dissociation, characterized by the rate of the ventricular contractions being slightly faster than those of the auricles so that there is no constant P-R or R-P interval. Theoretically, the difference between the two rhythms is due to retrograde conduction being present in A-V nodal rhythm in order to allow the auricles as well as the ventricles to respond to the new pace-maker in the A-V node, while in A-V dissociation retrograde conduction from A-V node is blocked so that the auricular contractions must arise above the A-V node, probably in the sino-auricular node (Cutts, 1937; Richardson, 1922). When ventricular bigeminy complicates A-V rhythm it is described