Analysis of the normal and abnormal vectorcardiogram in its own reference frame.

IN COMMON vectoreardiographic practice, vector loops are recorded in three plalne projections that are perpendicular to one another (frontal, sagittal, and horizontal planes). The arbitrary choice of these planes has been derived from body axes rather than from the spatial orientation of the vectorcardiogram or the heart itself. Several investigators1'-" have proposed, therefore, to replace the conventional projection planes by a reference systemn that is based on the spatial orientation of the largest veetoreardiographic (VCG) complex, the QRS loop. Schellougl reported in 1936 that spatial QRS loops of normal subjects form almost a perfect plane, the "QRS plane." A referenee frame based on the "QRS plane" becomes indepelndent of variability in QRS direction because auy QRS shift or rotation will always lead to a concomitant shift of the referenee system. The spatial orientation of such a referenee frame can be completely deseribed by onie term, an axis perpendicular to the QRS plane. Burger and Vaane9 introduced the term "polar vector" for this axis. The orientation of the QRS plane represents the spatial equivalent of Einthoveni's manifest QRS axis of the frontal plane12 whose diagnostic significance is well documented. Several investigators4-8 reported that in normal subjects QRS loops viewed in the QRS plane are more uniform in configurationi than in conventional plane projectiolns. Conse-