THE INTERCHANGEABILITY OF VECTORCARDIOGRAPHIC SYSTEMS.

Abstract The simultaneously recorded QRS complexes of the scalar leads of three orthogonal vectorcardiographic systems (SVEC-III, Frank, and axial) have been converted to digital form and examined by means of computer analysis for the characteristics of transformation between any two systems in 35 normal subjects. A set of individual transformation coefficients fitted by the method of least-squares for the entire phase of ventricular depolarization in each subject was obtained, so that when applied to the voltages of one lead system, the configurations of the QRS complex in the leads of the other system could be closely approximated. There was, however, considerable variation within the group, so that average transformation coefficients for the normal subjects sometimes gave very poor approximations of the desired set of scalar leads and vector loops from a given set. An attempt was made to determine whether this variation in transformation characteristics depended upon certain physical parameters, such as height, weight, age, body surface area, relative obesity, or orientation of the mean spatial electrical axis of the QRS. Mild trends were noted toward relating the components of Z in the Frank-to-axial transformation to body weight, and of the components of Z in the axial-to-SVEC-III transformation to the orientation of the mean spatial axis of the axial vectorcardiogram; otherwise, the variation in transformation coefficients appeared to be random. Our tentative conclusion is that, although interesting approximations can be obtained in the laboratory from the knowledge of average transformation coefficients, the practical interchangeability of quantitative information obtained from one lead system into that obtainable by another is seriously limited because of the wide range of biologic variation in transformation characteristics.