Analysis of the Normal and Abnormal Vectorcardiogram in Its Own Reference Frame

Abstract

Vectorcardiograms from 296 patients with a variety of ECG abnormalities were compared with normal standards obtained from 249 subjects without evidence of heart disease. A reference frame based on the spatial orientation of QRS loops rather than on conventional plane projections was used. Burger's polar vector and Schellong's QRS plane form the main parameters of such a reference frame. Spatial QRS orientation is defined by one term, the polar vector, which is perpendicular to the QRS plane. The direction of this vector can be determined through rotation of the QRS loop into its principal plane by means of a VCG lead resolver. Further analysis of QRS in its principal plane then becomes independent of inter-individual variability in spatial QRS direction. Separation between normal and abnormal was used as an indicator for the diagnostic quality of various measurements. Two corrected orthogonal lead systems designed by Schmitt and Frank were used for the study. These systems did not differ appreciably in the extent of normal ranges nor in the discrimination between normal and abnormal. The polar vector appeared as the best indicator for abnormalities. In 65 per cent of the pathologic cases this parameter was found outside normal limits. Measurements derived from the contour and principal axes of QRS planes improved the recognition rate for abnormalities. Ratios expressing the degree of QRS planarity, however, contributed little to diagnostic accuracy. The QRS-T angle obtained in the QRS plane improved the recognition rate mainly in the series with ventricular hypertrophies. It could be demonstrated that without evaluation of time and voltage criteria between 85 and 100 per cent of all pathologic records could be recognized as abnormal when the vectorcardiograms were analyzed in their own reference frame. Thus, it appeared that this method of analysis has a considerable diagnostic potential and compares favorably with those used more commonly in clinical electrocardiography and vectorcardiography.