Chapter 11: THE RESTING ELECTROCARDIOGRAM U WAVE
A number of hypotheses have been advanced to explain the genesis of the U wave. Foremost among them is the relationship to late repolarization of the Purkinje system. A criticism of this hypothesis is that the conducting system does not have sufficient mass to generate a large deflection at the body surface. The recent identification of another population of (M) cells between epicardium and endocardium may provide the necessary mass to produce not only U waves but also the J (or Osborn) wave characteristic of hypothermia.44 What sometimes appears to be a U wave merging with a T wave simple may be a notched T wave whose ascending or descending limbs are interrupted by differences in the end of the composite action potential of epicardial and M cells.14 The normal U wave, most prominent in leads V2 and V3, has the same polarity as the T wave and is approximately 10 percent of its amplitude. A large positive U wave may be due to hypokalemia and multiple antiarrhythmic drugs. In orthodox ECG interpretation, merging of T and U is still considered a stage in hypokalemia but can result from such drugs as quinidine and sotalol.14 According to Antzelevitch, repolarization of the His-Purkinje system was first suggested by Watanabe as the most likely cause of the "real" U wave.14 Causes of negative U waves are ischemia, hypertension, and occasionally, right ventricular enlargement.45
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...