Vectorcardiographic study of QRS loop in patients with left superior axis deviation and right bundle-branch block.

Thirty-four elderly patients with right bundle-branch block and left axis deviation were studied vectorcardiographically utilizing the McFee-Parungao system. Atherosclerosis, arterial hypertension, angina pectoris, cardiac enlargement, and heart failure were common clinical features in this series. Moreover, intermittent advanced degree of atrioventricular block was present in 10 out of the 34 patients. The vectorcardiograms might be readily classified into two basic patterns, types A and B. In type A (19 cases), the frontal plane loop was open-faced. The initial vectors were directed anteriorly, inferiorly, and to the right. The mid-temporal vectors were located in the left postero-superior octant, and the late portion of the loop was inscribed anteriorly to the right with conspicuous conduction delay. Those vectorcardiographic features associate the characteristic patterns of left superior intraventricular block with complete right bundle-branch block. The type B vectorcardiograms (15 cases) demonstrated anterior clockwise loops in the horizontal plane and superior counterclockwise loops in the frontal plane. From a review of the published reports and from personal data, the authors assume that both vectorcardiographic patterns may result from an abnormal spread of excitation resulting from bilateral branch conduction disturbances.