The U Wave



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Overview
U waves were described by Einthoven in 1903 and normally have same polarity as T waves

Pathophysiology
There are three hypotheses regarding the origin of the U wave :


 * 1) Late repolarization of Purkinje fibers,
 * 2) Late repolarization of some other portions of left ventricle,
 * 3) Alteration in the normal action potential shape by after potentials.

Appearance

 * 1) Ordinarily the U wave has the same polarity as the T wave and is 5 to 25% of the T wave amplitude.
 * 2) Tallest in leads V2 and V3, usually not greater than 1.0 mm.
 * 3) Considered abnormally large if the U wave is greater than 1.5 mm in any lead.

Differential Diagnosis of Causes of Abnormal U wave Prominence

 * Bradycardia
 * CNS disease
 * Drugs such as:
 * amiodarone
 * digitalis
 * disopyramide
 * epinephrine
 * phenothiazines
 * procainamide
 * quinidine


 * Electrolyte imbalance
 * Hypokalemia
 * Hypomagnesemia
 * Hypercalcemia


 * Hyperthyroidism
 * Left ventricular hypertrophy
 * Long QT syndrome
 * Mitral valve prolapse

Differential Diagnosis of Causes of U Wave Inversion

 * 1) Left ventricular hypertrophy (in I, V5, V6)
 * 2) Right ventricular hypertrophy (in II, III)
 * 3) Ischemic heart disease
 * May occur during anginal episode
 * U wave inversion during an exercise tolerance test is considered indicative of ischemia by some

Additional resources

 * ECGpedia: Course for interpretation of ECG
 * The whole ECG - A basic ECG primer
 * 12-lead ECG library
 * Simulation tool to demonstrate and study the relation between the electric activity of the heart and the ECG
 * ECG information from Children's Hospital Heart Center, Seattle
 * ECG Challenge from the ACC D2B Initiative
 * National Heart, Lung, and Blood Institute, Diseases and Conditions Index
 * A history of electrocardiography
 * EKG Interpretations in infants and children

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