Vector U loop in normal and hypertensive subjects.

The U loops of vectorcardiograms (VCG) were recorded in 100 normal subjects and 123 subjects with hypertension, using a direct-writing vectorcardiograph with memory function. These U loops were examined qualitatively and quantitatively. Subjects with hypertension were classified into four groups on the basis of electrocardiographic findings, and the correlation between findings on the U loop and the severity of hypertension was studied. The U loop of normal subjects was directed similarly to the T loop, showing either an arc or semilunar shape in the horizontal plane. In hypertensive subjects the U loop tended to be displaced anteroinferiorly and to the right with an increase in severity of hypertension. In these subjects the U loop was of slightly greater amplitude than in normal subjects, and was long and slender in shape. Anterior and rightward displacement of the U loop was also observed in hypertensive cases who showed no abnormality in the T wave of standard lead ECGs or in the T loop of the VCG. These findings seem useful as clinical parameters of the hemodynamic state in the early stage of hypertension. Based on these results, it was hypothesized that mechanical factors, such as stretch of the ventricular muscles induced by pressure loading of the left ventricle, may contribute greatly to genesis of the U loop.