The relation of the frontal QRS axis to the anatomic position of the heart

Summary

Deviation of the frontal QRS axis is found with a number of myocardial disorders. However, the wide normal range of this value has limited its usefulness as a diagnostic tool. In this study, two variables (the long axis of the heart and horizontal QRS axis deviation) were used to limit the normal range of frontal QRS axes of the 12-lead electrocardiogram. In accord with the changes expected with rotation of a dipole generator, these variables were combined to derive a new value, the predicted QRS axis. The predicted QRS axis represented the expected frontal plane projection of the QRS vectors based upon the long axis of the heart corrected for horizontal QRS axis deviation.

The coefficient between the predicted QRS axis and the frontal QRS axis was. 776, a much more precise prediction of frontal axis values than had previously been possible. To determine the approximate correlation which would be found with a perfect measuring system the correlation of attenuation was calculated (r=.901). This high correlation of attenuation is evidence that a substantial improvement in the prediction could be achieved by the use of corrected lead systems.