The order of ventricular excitation in human bundle-branch block

Abstract

Leads in which one electrode (the exploring electrode) is placed close to the heart and the other (the indifferent electrode) at a distance from it are semidirect leads. In experiments on dogs serial semidirect leads were taken from the surface of a pad of gauze soaked in warm normal salt solution and laid upon the exposed heart. The galvanometer connections were made in such a way that relative negativity of the exploring electrode yielded an upward deflection in the completed curve. In animals in which bundle-branch block had been produced, the chief upstroke of the ventricular complex occurred early in those semidirect leads in which the exploring electrode was close to the surface of the contralateral, and late in those leads in which this electrode was close to the surface of the homolateral ventricle. In the former case was usually negative; in the latter case, usually positive. In precordial leads the exploring electrode is placed on the precordium and the indifferent electrode on the left leg. Serial precordial leads in cases of clinical bundle-branch block of the common type yield results similar to those obtained by semidirect leads in experimental left branch block. In the rare type of bundle-branch block they yield results similar to those obtained in experimental right branch block. The common type of bundle-branch block is left branch block; the rare type, right branch block. The chief ventricular upstroke of semidirect leads, in which the exploring electrode is placed close to the ventricular surface, corresponds to the intrinsic deflection of direct leads from the ventricles in which a single contact is placed upon the muscle.