The effect of posture upon axis deviation in human bundle branch block

Abstract

1. 1. A case of bundle branch block is described in which the block apparently alternated between the right and left branches. The changes in the electrocardiographic pattern were subsequently duplicated by alteration of the patient's posture. 2. 2. The effect upon the standard and augmented unipolar limb leads and upon the precordial leads of changing from the supine to either right or left lateral postures has been studied in forty cases of bundle branch block, twenty of the right and twenty of the left bundle branch. 3. 3. The position of the electrical axis has been measured in each case in the three postures and the electrical position of the heart determined from the augmented unipolar limb leads. 4. 4. In left bundle branch block the axis shifted more than 30° in eight of nineteen cases; in six instances the shift exceeded 60°. The greatest shift was 185°. The direction of shift was, with one exception, invariably to the right on assumption of a lateral posture. The electrical position of the heart became more vertical in all six patients in whom it was altered. 5. 5. In four patients with left bundle branch block, an upright QRS in Lead I became negative so that right axis deviation and apparent right bundle branch block appeared in the lateral posture. In three patients assumption of a lateral posture caused a negative QRS in Lead III to become upright so that the discordant pattern of left bundle branch block became concordant. In all of these patients the precordial leads showed delay in the intrinsic deflection over the left precordium in all postures. 6. 6. In right bundle branch block, assumption of one or the other lateral posture led to a shift of axis of more than 30° in seven of twenty patients; in six of these, the shift was to the right. In no case did the electrocardiographic pattern simulate left bundle branch block, and the electrical position of the heart was never grossly altered. 7. 7. It is concluded that the limb leads are unreliable as a guide to the side of bundle branch block in some cases, but that the precordial leads are little affected by changes of posture. The importance of taking electrocardiograms in a standard posture is re-emphasized.