Atrial dissociation.

Atrial dissociation is characterized by two sets of independent P waves on the electrocardiogram and two atrial beats independent of each other. One atrium is under the control of the dominant pacemaker (sinus node) which also controls the ventricles, while the other atrium or part of the other atrium is under the control ofan ectopic pacemaker, resulting in unilateral ectopic atrial rhythm, because the two pacemakers do not interfere with each other. The unilateral ectopic rhythm may be in the form of slow ectopic atrial rhythm, atrial tachycardia, flutter, or fibrillation. The unilateral ectopic rhythm never conducts to the ventricles. Atrial dissociation has been observed in the exposed heart of the experimental animal. Condorelli (I929) produced atrial dissociation by ligating the left anterior atrial artery, which resulted in sinus rhythm controlling the right atrium, and fibrillation in the left atrium. This phenomenon has been seen in the human heart (Scherfand Cohen, I964). The following patient is reported in order to illustrate atrial dissociation with a review of some of the cases already reported.