The Scalar Electrocardiogram, Vectorcardiogram, and Exercise Electrocardiogram in the Assessment of Congenital Aortic Stenosis

Abstract

The standard ecg, the cube vectorcardiogram, and lead V6 exercise ecg have been evaluated in patients with congenital aortic stenosis, assessed at cardiac catheterization. The most reliable indicators of significant aortic stenosis in the standard ecg are ST- and T-wave changes in left precordial leads in the presence of increased voltage of the R wave. In 26% of 69 cases with peak systolic gradients of more than 40 mm. Hg, these changes were absent. All these patients., however, were children or young adults. Changes in repolariza-tion are obviously of lesser importance in older patients, since the possibility of coronary artery disease always exists. Vectorcardio-grams were recorded in 40 patients and compared with those obtained from 45 normal subjects. A significant difference was found in the direction of QRS vectors at 0.03, 0.035 second, as well as at the time of maximum excursion, of the QRS loop in the horizontal plane in almost all patients with aortic stenosis, irrespective of severity. Furthermore, a positive correlation could be demonstrated between the left ventricular systolic peak pressure and the direction and magnitude of the maximum QRS vector in the horizontal plane. These findings indicate that increased left ventricular pressure work may be assessed by measurement of the overall electrical activity at the time of maximum leftward and posterior excursion of the QRS loop. In 10 of the 11 cases of severe aortic stenosis with normal or equivocal ecgs, the vectorcardiograms showed definite evidence for significant left ventricular hypertrophy. Finally, the exercise ecg was found helpful in that in 4 patients with normal resting ecgs abnormalities occurred suggesting myocardial ischemia. A normal exercise ecg did not always indicate normal hemodynamics, however. In the routine clinical assessment of aortic stenosis the ecg remains the most useful screening procedure. The cube vectorcardiogram, however, has proved to be of great accuracy in selecting those patients who, despite a normal ecg, have significant aortic stenosis. Both changes in direction and magnitude of vectors are factors not readily available in the routine ecg and can be used in a quantitative sense to identify patients in whom cardiac catheterization is imperative.