by Gail Belsky. The term sleep disorder may suggest someone tossing and turning all night, but lying awake for hours with insomnia is just one example of many conditions that affect how you sleep and function during the day. In fact, you can have a sleep disorder and not even know it. Next: How long to snooze.
A U wave as seen on ECG. An electrocardiogram of an 18-year-old man showing U waves, most evident in lead V3. The U wave is a wave on an electrocardiogram that is not always seen. It is typically small, and, by definition, follows the T wave. U waves are thought to represent repolarization of the papillary muscles or Purkinje fibers.
P wave, the component of the cardiac cycle shown on an electrocardiogram as an inverted U-shaped curve that follows the T wave and precedes the QRS complex. It represents atrial depolarization. wave, the component of the cardiac cycle shown on an electrocardiogram as an inverted U-shaped curve that follows the T wave and precedes the QRS complex. It represents atrial depolarization.