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
PREVIOUS | NEXT
Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27
Copyright ©2001-2002 The McGraw-Hill Companies. All rights reserved.
For further information about this site contact tech [email protected].
Last modified: August 10, 2002 .
.■WJcrniiji: i^'Jlli MiÇftairJiilHjnhlfMftliï
Was this article helpful?
Do You Suffer From High Blood Pressure? Do You Feel Like This Silent Killer Might Be Stalking You? Have you been diagnosed or pre-hypertension and hypertension? Then JOIN THE CROWD Nearly 1 in 3 adults in the United States suffer from High Blood Pressure and only 1 in 3 adults are actually aware that they have it.