What causes U wave?

As a cardiac electrophysiologist, I can provide insight into the phenomenon of the U wave on an electrocardiogram (ECG). The U wave is indeed a deflection on the ECG that follows the T wave and precedes the P wave in the next cardiac cycle. It is often smaller and less prominent than the T wave, which is why it may not always be visible, especially in individuals with a rapid heart rate or in the presence of other ECG abnormalities. The exact cause of the U wave is not entirely understood, but several theories have been proposed. One of the most widely accepted theories is that the U wave represents the repolarization of the Purkinje fibers within the ventricles. These fibers are part of the electrical conduction system of the heart and are responsible for the rapid spread of electrical impulses during ventricular contraction. Several factors can affect the visibility and prominence of the U wave, including: 1. Electrolyte imbalances: Abnormal levels of potassium, calcium, or magnesium can alter the U wave's appearance. 2. Autonomic nervous system activity: Changes in heart rate or autonomic tone can influence the U wave. 3. Drug effects: Certain medications, such as those that affect the heart's electrical activity, can cause changes in the U wave. 4. Cardiac conditions: Conditions that affect ventricular repolarization, such as long QT syndrome, can also result in a prominent U wave. It's important to note that while the U wave is often benign, in some cases, it can be associated with certain cardiac conditions or electrolyte disturbances. Therefore, it is evaluated in the context of the entire ECG and the patient's clinical presentation.

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.