Longitudinal Dissociation

LONGITUDINAL DISSOCIATION, a disruption in the coordinated contraction of the ventricles, as opposed to the disorder of coordination in the activity of the atria and ventricles, so-called transverse dissociation (see Heart Block). In normal conditions, the ventricles contract almost simultaneously (the left ventricle, according to Fredericque and Stossen, precedes by 0.03 seconds). An extreme case of longitudinal dissociation is hemisystole (see), when only one ventricle beats while the other is completely at rest. Asynergism in the activity of the ventricles can be assumed as a result of changes in the function of the innervation apparatus due to pathological conditions of this apparatus or under the influence of pharmacological poisons, as well as a result of anatomical changes in the heart itself and in particular its conduction system. In hypertrophy of one of the ventricles, it, with relatively increased contractile activity, in the stage of complete compensation depending on the muscle mass, may lag in contraction from the non-hypertrophied (or less hypertrophied) ventricle. In the stage of compensation disorder, the dynamics of the cavities may change and give rise to a different sequence in their contraction (dynamic dissociation). A more reliable understanding of longitudinal dissociation exists only in relation to those cases where it is caused by blockage of one of the branches of the His bundle (see Heart Block). In this case, the contraction of the ventricle, the branch of which is blocked, is delayed compared to the other, since the impulse coming from the atria apparently reaches it by an indirect route - through the ventricle whose branch conducts. The presence of longitudinal dissociation can be assumed in some forms of gallop rhythm (see). The electrocardiographic manifestation of longitudinal dissociation should be considered as the picture of blockage of one of the legs of the His bundle (fig. - see Vol. VI, p. 238).