What causes U waves?

As a cardiac electrophysiologist, I specialize in the study of the electrical activity of the heart, which includes understanding the various components of an electrocardiogram (ECG). The U wave is indeed a component of the ECG that follows the T wave and is not always easily observed due to its small amplitude. The U wave is believed to be caused by several factors, including: 1. Repolarization of the Purkinje fibers: The Purkinje fibers are a part of the cardiac conduction system that helps to synchronize the contraction of the ventricles. The repolarization of these fibers is thought to be one of the primary causes of the U wave. 2. Electrolyte imbalances: Particularly, hypokalemia (low potassium levels) and hypomagnesemia (low magnesium levels) are known to be associated with the prominence of U waves on the ECG. 3. Prolonged QT interval: A prolonged QT interval, which can be due to various reasons including genetic conditions, certain medications, or electrolyte disturbances, can lead to the appearance of U waves. 4. Transmural heterogeneity: This refers to the differences in the repolarization of the ventricular myocardium at various depths. The U wave may be more pronounced in conditions where there is a significant transmural heterogeneity. 5. Afterdepolarizations: These are abnormal electrical activities that can occur after the main depolarization wave and are another potential cause for the appearance of U waves. 6. Drug effects: Certain medications, such as class III antiarrhythmic drugs, can prolong the action potential duration and are known to cause U waves. It's important to note that while U waves are often benign, they can also be associated with certain pathological conditions, such as hypokalemia, hypothermia, or certain genetic channelopathies. Therefore, the presence of U waves should be interpreted in the context of the patient's clinical presentation and other ECG findings.

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.