Auriculoventricular Rhythm and Digitalis

Auriculoventricular rhythm, a condition in which the A-V node assumes rhythmicity independent of the sinus node, is due to one of two causes; depressed irritability of the sinus node or enhanced irritability of the A-V node.Experimentally both types have been produced, the former by tying off (Engelmann1), injuring (Hering2), or cooling (Ganter and Zahn 3) the sinus node, the latter by stimulating the A-V node either directly (Lohmann4) or through the left acceler- ator (Hering;5 Rothberger and Winterberg6).Meek and Eyster7 reviewed and extended the experimental work.By means of electrodes connected with a string galvanometer and applied direct to the heart they obtained evidence that in A-V rhythm the electrical activity originates in the A-V node.Clinically, both types of the A-V rhythm have been observed, the type in which the irritability of the sinus node is depressed, character- ized by a slow rhythm, and the type in which the irritability of the A-V node is enhanced, characterized by a relatively rapid rhythm.The former, though rare, is much the more common of the two.Whites distinguishes further between A-V rhythm and simple ventricular escape.In the former the excitation wave arises from the A-V node alone, in the latter from both nodes simultaneously.He bases the distinction on the form of the wave which is known to be inverted or upright according as the excitation wave arises near the A-V node or near the sinus node.A-V rhythm is, therefore, char¬ acterized by an inverted wave, simple ventricular escape by an upright wave.Of the two conditions A-V rhythm is much the more permanent.The accompanying table indicates the variety of the conditions in which A-V rhythm occurs, together with the outcome of the cases.No death occurred as a result of A-V rhythm alone.In the fatal cases the postmortem examination revealed ample causes for death