[Vectorcardiographic manifestations of left intraventricular conduction disorders].

Both, the vectorcardiographic changes produced by the various degrees of left bundle branch block and these observed with the different types of left distal block, are described. When a "wave jumping" phenomenon exists, the vectorcardiographic changes are more characteristic in the horizontal plane than in the frontal plane and can be interpreted satisfactorily in basis of the ventricular activation sequence. The normal counterclockwise rotation of the horizontal vectorcardiogram persists in the presence of left bundle branch block of slight and moderate degrees, since the electromotive forces of the free left ventricular wall are still predominant. In the majority of intermediate degree blocks, the middle portion of the RH loop develops with a clockwise rotation and general aspect with a clockwise rotation and the general aspect of the ventricular loop resembles an eight figure. This is due to the electromotive forces originated by the delayed depolarization of the left septal mass that starts to predominate. With advanced degrees of block, the largest portion of the RH loop shows a clockwise rotation, as well as marked notchings and slurrings. The initial anterior portion of the horizontal vectorcardiogram does not disappear, but is situated to the left of the anterior-posterior axis with a counterclockwise rotation (first right septal vector). Otherwise, the direct electrical sign of left distal block emphasized: evidence of delayed activation in a limited zone of the homolateral ventricle. This local delay gives rise to an asynchronism of the activation phenomenon between the upper and lower regions of the ventricle. The diagnosis of left bifascicular block is based essentially on the evidence of unequal delay of the activation sequence in the basal regions and in the inferior ones of the homolateral ventricle and also on the frequent persistence of the first left septal vector.