Dissociation With Interference, Reciprocal Rhythm, and Coronary Sinus Rhythm

Dissociation with interference and reciprocal beats have many features in common. They have to be differentiated from one another and from auricular parasystole. Herrmann and Ashman (1930) stressed the importance of the auricular rhythm and polarity of the P waves in the bipolar limb leads as differential criteria between the two rhythms, regular auricular rhythm and positive P waves indicating dissociation with interference. Either may occur when the auriculo-ventricular node is an independent pacemaker, or more rarely, when there is a heterogenetic centre of impulse formation in the ventricles. In both orthograde conduction remains intact although it may be impaired. Retrograde conduction is completely blocked in dissociation with interference whereas in reciprocal rhythm it is not altered, although for reciprocal beats to occur it is usually delayed to a certain critical level. The recognition of these disturbances of conduction is important in clinical medicine, for most reported cases have underlying organic heart disease, or are caused by intoxica- tion such as that due to digitalis or to an increased content of pressor substances in the blood. Their presence can only be detected by graphic methods, and on ordinary clinical examination they are likely to be confused with sinus rhythm, or an idioventricular rhythm with extrasystoles in the ordinary sense. Thus either rhythm may be responsible for one variety of pulsus bigeminus.