On axis deviation in human bundle branch block

Abstract

Fifty-four cases with records showing both normal intraventricular conduction and bundle branch block have been collected; 192 records were available, ninety showing bundle branch block, ninety-two showing normal intraventricular conduction, and ten showing both bundle branch block and normal conduction. The axis deviation has been measured in each record and the average position of the electrical axis of QRS during normal conduction compared with that during bundle branch block. When right or left bundle branch block appeared or disappeared there was a significant change in the direction of the electrical axis of QRS (15° or more) in less than one-half of the cases, and the average change was 12° to the left in left bundle branch block and 12° to the right in right bundle branch block. When a significant change of axis was associated with the appearance of bundle branch block, the direction of the change was always to the left when the block was of the left bundle branch and, except in one case, to the right when the right bundle branch was blocked. Even in cases in which a significant change of axis was found, the general pattern of the bundle branch block electrocardiogram conformed closely to the pattern with normal intraventricular conduction. Factors, other than the bundle branch block, that might have caused a shift of the electrical axis have been discussed; it is believed that they did not materially influence the averaged results. It is concluded that the axis deviation and the general pattern of the electrocardiogram are not greatly modified by the appearance of bundle branch block, and that the axis deviation associated with right and left bundle branch block is due principally to the position of the electrical axis of QRS before the bundle branch block appeared. Certain implications arising from this conclusion have been briefly discussed.