Clockwise Inscription of the Horizontal QRS Loop of the Vectorcardiogram

SUMMARY A series of 864 vectorcardiograms (recorded with the Frank lead system) have been reviewed; 115 cases (13.3 per cent) presented a clockwise inscribed QRS loop in the horizontal plane. This clockwise inscription represents an important diagnostic finding. A study of its significance has been undertaken with the use of special perforated cards: main orientation of the QRSsĚ loop, clinical diagnosis of the heart disease, and electrical diagnosis were correlated. The QRS loops showing a clockwise inscription with an anterior orientation (51.3 per cent) represented, almost without exception, right ventricular overload and/or right bundle branch block. In the latter case, the major portion of QRS was mainly situated in the left anterior quadrant; contrariwise, the loop was shifted to the right, if right ventricular overload was present. Posterior and rightward inscription of QRS was relatively rare (14.7 per cent). Nine cases presented right ventricular overload, generally severe, without bundle branch block. Such an orientation has not been explained in these instances. Tracings displaying a clockwise inscription of QRS with a left posterior orientation (31.3 per cent) were very suggestive of left bundle branch block, either of the "complete" or "incomplete" variety, and either isolated or complicated with left ventricular overload or anterior myocardial infarction. On rare occasions, left bundle branch block loops presented a slight displacement into the right posterior quadrant.