Left bundle branch block with left-axis deviation: an electrophysiologic approach.

Abstract

In an attempt to explain QRS left-axis deviation (LAD) in left bundle branch block (LBBB), 69 patients with LBBB were studied. The patients were separated into 2 groups. Group A included 60 patients with a QRS axis of +80 degrees to -55 degrees (average -11 degrees) and Group B included 9 patients with a QRS axis of -60 degrees. In all patients, a point was detected on the apex of the right ventricle at which activation was simultaneous with the beginning of ventricular depolarization (V-apex = 0). Ventricular stimulation at this point gave a monomorphic response with a QRS axis of -60 degrees and QS in D2 and D3. Minor conduction aberrations related to the relative refractory period of the His Purkinje network were found during atrial premature beats in 40 patients in Group A (and always as LAD of the QRS axis [average 24.6 degrees]) and in 4 patients in Group B. In Group B, these aberrations were in the form of a disappearance of the r2 wave with a QRS axis similar to that achieved through stimulation of the right ventricle apex. Given this aberration, one may conclude that the left bundle branch plays a role in the depolarization of the left ventricle. Blocking it brings the QRS axis closer to that obtained by stimulation of the point of primary depolarization of the right ventricle. Thus, LBBB must have a monomorphic morphology. If not, the left branch is the location of slowed, but persistent, conduction.