Interference Dissociation in Contrast to Reciprocating Rhythm.

Abstract

There is apparently no certain way of distinguishing between interference dissociation and reciprocating beats in the individual case, barring some accidental irregularity which affords a certain clue. There are, however, 2 criteria which serve to differentiate the conditions, (1) auricular regularity or irregularity and (2) P wave direction. If P waves are clearly upright in leads I and II or I, II, and III, it becomes certain that one is dealing with interference and not with reciprocation. If the auricles are regular, as is true in one of our cases, then the mechanism is in all probability interference. It would be a rare coincidence which would make the progressive prolongation of retrograde conduction time such as to make the auricle regular; reciprocation therefore practically always presents an irregular contra-directional auricular activity.

Electrocardiograms are presented to call attention to the electrocardiographic differential diagnosis between “Interferenz Dissoziation” (Mobitz 1 ) or Dissociation with Interference (Wenckebach and Winterberg 2 ) and the entirely different mechanism of reciprocating beats for which it may be mistaken. The tracings show some conduction defect also, but this is not at all related to the unusual mechanism of interference which does not require the presence of defective conduction for its inception.

Interference dissociation will necessarily appear when there is free A-V conduction, complete V-A block, and an auricular rhythm which is slower than the ventricular. Under these conditions, those auricular impulses which follow the idioventricular beats by a great enough interval will reach the ventricle, since they encounter no absolutely refractory muscle in the conducting path. The ventricular beats they arouse will be premature. In our cases, as in the great majority of reported examples, the idioventricular pacemaker is supraventricular, i. e., in the His bundle or A-V node.