What does a U Wave on an EKG represent?

A U Wave on an EKG represents the repolarization of the Purkinje fibers or the late phase of ventricular repolarization. It is commonly seen following the T wave and can indicate various electrophysiological conditions. One of its notable associations is with possible low potassium levels in the bloodstream, known as hypokalemia. When potassium levels drop, the heart's electrical activity can become altered, leading to distinct changes on the EKG including the prominence of the U wave.

In contrast, the other options do not have a direct relationship with the presence or significance of the U wave on an EKG. High sodium levels do not specifically relate to the U wave. Oxygen saturation is monitored through pulse oximetry rather than EKG, and while coronary artery disease can affect overall cardiac rhythm and function, it is not directly indicated by the U wave. Therefore, the association of the U wave with possible low potassium levels makes it the correct explanation.