XII. Polarity and Amplitude of the U Wave of the Electrocardiogram in Relation to that of the T Wave

Abstract

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.

Sympathomimetic Infusion and Cardiac Repolarization: The Normative Effects of Epinephrine and Isoproterenol in Healthy Subjects

“…The T‐ and U‐wave amplitudes were measured in lead V3 using the QT‐Guard program by identifying the voltage at the peak of the T and U waves, respectively. Lead V3 was chosen because this lead has previously been reported to have the highest prevalence of U waves of all standard ECG leads 21,22 . At high HRs, no further amplitude measurements were made if the U waves became superimposed with either the T wave of the same ECG complex or the P wave (P) of the following ECG complex such that distinct peaks were no longer visible.…”

“…Lead V3 was chosen because this lead has previously been reported to have the highest prevalence of U waves of all standard ECG leads. 21,22 At high HRs, no further amplitude measurements were made if the U waves became superimposed with either the T wave of the same ECG complex or the P wave (P) of the following ECG complex such that distinct peaks were no longer visible. Our measurements have been shown to highly reproducible with minimal measurement variability in a separate group of 25 normal subjects.…”

Large negative U waves associated with hypokalemia

“…Negative U waves, however, are important findings in the ECG because their presence is highly specific for severe hypertension or structural heart disease [1,2] . In patients with hypertension, the negative U waves typically follow negative T waves (the strain pattern); positive T waves followed by negative U waves are uncommon [3,4] . Normalization of the blood pressure may result in less negativity of the U waves or even in the U waves becoming upright [5] .…”

Relationship between Arterial Pressure and Negative U Waves in Electrocardiograms

“…It is possible that in patients with coronary disease, negative U waves following exercise are also a manifestation of the pressor effect of exercise and not of the associated coronary arterial disease. Surawicz et al 3 have noted, without reporting simultaneous arterial pressure measurements, that in some cases the faster heart rate was accompanied by a negative, and a slower rate by a positive U wave. In our study the polarity of the U waves was not influenced by the heart rate; in all patients in whom sodium nitroprusside was given, conversion of negative U waves occurred as a result of the arterial pressure fall and in spite of the slight increase in heart rate ( fig.…”