U wave

The U wave is a wave on an electrocardiogram that is not always seen.

U waves are thought to represent repolarization of the papillary muscles or Purkinje fibers.

The electrocardiogram may show flattening of T waves and prominent U waves.

An inverted U wave may represent myocardial ischemia or left ventricular volume overload.

Patients on chlorpromazine therapy exhibit abnormalities on the electrocardiographic T and U waves.

First-degree heart block, ectopic atrial rhythms, nodal escape, ventricular premature complexes, ST depression, and U waves may all be found.

The T wave follows the S wave, and in some cases an additional U wave follows the T wave.

Other ECG effects include a wide notched P wave, wide QRS complex, depressed ST segment, and U waves.

Some electrocardiographic (ECG) findings associated with hypokalemia include flattened or inverted T waves, a U wave, ST depression and a wide PR interval.

Patients may have normal resting T and U waves that become enlarged and abnormal, both in contour and duration, during intense physical or emotional stress just before the onset of torsades de pointes.

Additional features that are sometimes present include a prominent U wave, abnormal contour of T or TU waves, T wave alternans, a subnormal spontaneous sinus rate (especially in children), and sinus pauses.

Due to prolonged repolarization of ventricular Purkinje fibers, a prominent U wave occurs, that is frequently superimposed upon the T wave and therefore produces the appearance of a prolonged QT interval.

Prominent U waves are most often seen in hypokalemia, but may be present in hypercalcemia, thyrotoxicosis, or exposure to digitalis, epinephrine, and Class 1A and 3 antiarrhythmics, as well as in congenital long QT syndrome, and in the setting of intracranial hemorrhage.