U vector loops were obtained by electrical dissection from 53 patients, composed of 11 cases of right ventricular hypertrophy, 21 cases of right branch block and 21 cases of myocardial infarction. The U loop of right ventricular hypertrophy and right bundle branch block resembled that of normal subjects. It had a shape like a small, slightly curved club and was inscribed in the direction of continuance of the terminal limb of the T loop. The U loop of myocardial infarction was frequently larger

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... than normal U loops and began with a marked bend at the T-U junction and extended in various directions. It resembled that of left ventricular hypertrophy, but the U loop abnormality in myocardial infarction was usually more marked than in left ventricular hypertrophy. It was suggested that the U vector was directed toward the location of myocardial infarcts. But because of technical difficulty this could not be confirmed. INCE our previous study1) on U vector loop in normal subjects and in those with left ventricular hypertrophy, U vector loop was further studied in patients with right ventricular hypertrophy, right bundle branch block and myocardial infarction. This part of the vector loop could only be studied by the method of differential vectorcardiography,2) because the U vector loop is very small and merges with the ST-T and P loops and the initial and terminal portions of the QRS loop.