U, THE SIXTH WAVE OF THE ELECTROCARDIOGRAM

U waves in ventricular hypertrophy: possible demonstration of mechano-electrical feedback

The relation between ventricular function and electrocardiographic evidence of hypertrophy (by voltage criteria, "strain", and U wave inversion) was examined by means of M mode echocardiography and apex cardiography in 73 patients with diseases associated with left ventricular hypertrophy and 10 normal volunteers. In patients with disease, left ventricular cavity dimension and fractional shortening were unrelated to electrocardiographic findings, but left ventricular posterior wall thickness was greater in those with strain or U wave inversion. Without U wave inversion, hypertrophy and strain were weakly related to diastolic abnormalities, but the addition of U wave inversion was strongly associated with a reduced rate of early diastolic posterior wall thinning, prolonged isovolumic relaxation time, delayed mitral valve opening after minimum cavity dimension, and a pronounced increase in transverse dimension during the isovolumic period suggesting incoordinate relaxation. It is concluded that, whereas a negative U wave frequently occurs in association with the pattern of left ventricular hypertrophy or strain, it alone is strongly related to abnormalities of isovolumic relaxation. The close relation between incoordinate relaxation and U wave inversion, events which occur virtually simultaneously during the isovolumic period, suggests a mechanical influence on U wave genesis.

Abnormal U waves in the electrocardiogram in subarachnoid haemorrhage

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Polarity and amplitude of the U wave of the electrocardiogram in relation to that of the T wave

The ratio of the amplitude of the QRS complex to the amplitude of the U wave varies in different leads of the same electrocardiogram. In the majority of electrocardiograms, the U wave has the same polarity as the T wave and the ratio of the U wave and T wave amplitude is relatively constant in all leads. The tallest positive U wave is usually observed in the area of leads V 2 to V 4 . The deepest negative U wave is usually observed in the area of leads V 5 to V 6 . Secondary changes of the T wave are very frequently accompanied by similar changes of the U wave. T-wave changes caused by myocardial infarction and digitalis are usually not accompanied by changes of the polarity of the U wave.

The electrocardiograms of 297 cases of hypertension were divided into 6 groups on the basis of the relationship between the polarity of the T wave and the U wave. Both waves were positive in all precordial leads in 48.1 per cent of the cases. Negative U waves were found in 21.8 per cent of the cases and these were predominantly in the leads with negative T waves. A negative T wave in the left precordial leads was accompanied most frequently by a negative, less frequently by an isoelectric, and least frequently by a positive, U wave. An inverted U wave in the presence of an upright T wave was found in only 2.8 per cent of the cases. A change from a negative to a positive or isoelectric U wave was observed after slowing of the heart rate, a drop in blood pressure, and nitroglycerin administration.

Isolated U wave negativity

Inversion of U as the only abnormal electrocardiographic finding is here shown to be the first change to occur in certain cases of hypertension, coronary artery sclerosis, and other organic heart disease. It is also found in association with certain metabolic and electrolyte changes. Its recognition will enhance the value of the electrocardiogram in clinical diagnosis.

The lesser electrocardiographic signs of cardiac pain

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