How does the U wave appear?

As a domain expert in cardiology, I can explain the appearance of the U wave on an electrocardiogram (ECG). The U wave is a deflection on the ECG that occurs after the T wave and before the P wave of the subsequent beat. It is not always visible due to its small amplitude, which can make it challenging to distinguish from baseline noise or the T wave itself. The U wave is believed to be caused by several factors, including repolarization of the Purkinje fibers, which are a part of the cardiac conduction system that helps to synchronize the contraction of the ventricles. Other theories suggest that the U wave may be related to the repolarization of the papillary muscles or the His-Purkinje system, or it could be a result of differences in the rate of repolarization between the endocardium and epicardium. The appearance of the U wave can be influenced by various conditions and substances. For instance, hypo- or hyperkalemia (abnormal levels of potassium in the blood) can affect the prominence of the U wave. Additionally, certain medications, such as class III antiarrhythmic drugs, can also cause or accentuate the U wave. In summary, the U wave is a small wave on the ECG that follows the T wave and is thought to represent repolarization of certain cardiac tissues. Its visibility can vary, and it can be influenced by electrolyte levels and medications.

The 'U' wave is a wave on an electrocardiogram (ECG). It is the successor of the 'T' wave and may not always be observed as a result of its small size. 'U' waves are thought to represent repolarization of the Purkinje fibers.