U Wave
It is a small deflection that comes after the T wave of ventricular repolarization and may not always be observed as a result of its small size.
‘U’ waves are thought to represent repolarization of the Purkinje fibers. However, the exact source of the U wave remains unclear.
1-2mm in size
It is generally upright except in the aVR lead and is often most prominent in leads V2 to V4.
Seen more prominent in patient with bradycardia