U WAVE IN ECG AND ITS ABNORMALITIES

1. U WAVE
Dr.G.VENKATA RAMANA
MBBS DNB FAMILY MEDICINE

2. • U wave Overview
• Small (0.5 mm) deflection immediately following the T
wave
• Usually in the same direction as the T wave
• Best seen in leads V2 and V3
• More commonly seen when patients are bradycardic
• Source of the U wave
• Unknown
• Three common theories regarding its origin are:
• Delayed repolarisation of Purkinje fibres
• Prolonged repolarisation of mid-myocardial “M-cells”
• After-potentials resulting from mechanical forces in the
ventricular wall

3. • Features of Normal U waves
• Normally goes in the same direction as the T wave
• Size is inversely proportional to heart rate: the U wave grows bigger
as the heart rate slows down
• Generally become visible when the heart rate falls below 65 bpm
• The voltage of the U wave is normally < 25% of the T-wave voltage:
disproportionally large U waves are abnormal
• Maximum normal amplitude of the U wave is 1-2 mm

4. • Abnormalities of the U wave
• Prominent U waves
• Inverted U waves
• Prominent U waves
• U waves are described as prominent if they are
• >1-2mm or 25% of the height of the T wave

5. • Causes of prominent U waves
• Prominent U waves most commonly found with:
• Bradycardia
• Severe hypokalemia
• Prominent U waves may be present with:
• Hypocalcemia
• Hypomagnesemia
• Hypothermia
• Raised intracranial pressure
• Left ventricular hypertrophy
• Hypertrophic cardiomyopathy
• Drugs associated with prominent U waves:
• Digoxin
• Phenothiazines (thioridazine)
• Class Ia antiarrhythmics (quinidine, procainamide)
• Class III antiarrhythmics (sotalol, amiodarone)
• Note Many of the conditions causing prominent U waves will
also cause a long QT

6. Prominent U waves due to sinus bradycardia

7. U waves associated with hypokalemia
Prominent U waves in a patient with a K+ of 1.9

8. U waves associated with left ventricular hypertrophy

9. U waves associated with digoxin use

10. U waves associated with quinidine use

11. • Inverted U waves
• U-wave inversion is abnormal (in leads with upright T waves)
• A negative U wave is highly specific for the presence of heart
disease
• Common causes of inverted U waves
• Coronary artery disease
• Hypertension
• Valvular heart disease
• Congenital heart disease
• Cardiomyopathy
• Hyperthyroidism
• In patients presenting with chest pain, inverted U waves:
• Are a very specific sign of myocardial ischaemia
• May be the earliest marker of unstable angina and evolving
myocardial infarction
• Have been shown to predict a ≥ 75% stenosis of the LAD / LMCA
and the presence of left ventricular dysfunction

12. Unstable angina
Inverted U waves in a patient with unstable angina

13. Inverted U waves in Prinzmetal angina

14. NSTEMI
Note the subtle U-wave inversion in the lateral leads (I, V5 and
V6) in this patient with a NSTEMI; these were the only abnormal
findings on his ECG