U waves were described by Einthoven in 1903 and normally have same polarity as T waves^[1]

There are three hypotheses regarding the origin of the U wave^[2]:

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.

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.^[3]

• 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

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

• 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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