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 arch preceding the QRS complex. Q wave-the first negative (downward) deflection of the complex. In some leads, it will not be present. In some cases, the complex begins with an R wave.R wave-the first positive (upward) deflection of the QRS complex.RS-the complex represents the depolarization of the ventricles. This is followed by an isoelectric segment. T wave-this represents ventricular repolarization. Atrial Contraction-the atria mechanically contract starting at the beginning of the P wave, until the beginning of the QRS complex.