Effects of left anterior fascicular block on the depolarization process as depicted by total body surface mapping.

To examine the effects of left anterio fascicular block (LAFB) on the depolarization process as manifested on the body surface, 142 lead maps were recorded in 25 subjects with LAFB. Three abnormalities were detected: (1) In the early and mid portion of QRS, twenty of 25 subjects showed abnormal anterior superior positivity, starting in the precordial area and proceeding toward the left subclavicular area. The explanation was thought to be the relatively delayed, dysynchronous, and superiorly directed altered sequence of depolarization of the anterior left ventricle. (2) All the subjects showed left lower abnormal negativity. This was thought to represent the unopposed receding activation front after the left ventricular breakthrough posteroinferiorly and also the negative aspect of the abnormally directed superior positivity. (3) Eleven subjects showed abnormal negative potentials at the right lower chest. This was thought to represent the partially unopposed activation fronts of the right ventricular free wall seen after right ventricular epicardial breakthrough, because of the absence of the usually cancelling normal forces from the anterior portion of the left ventricle. Additionally, the surface manifestation of the septal depolarization was found to be indistinguishable from nornal. This study further enhances our understanding of the altered sequence of depolarization in LAFB, as manifested on the body surface instant-by-instant.