U wave

Introduction

The U wave is a small (0.5 mm) deflection immediately following the T wave.

Etiology

The mechanism is questionable, but it is assumed:

  • delayed repolarization of the ventricular septum
  • delayed repolarization of some parts of the ventricles
  • repolarization of Purkinje fibers

ECG features

  • U wave is concordant with the T wave (has the same polarity as a T wave)
  • Amplitude is approx. 0.5 - 2mm 
  • Best visible in V2-V3
  • Is present in bradycardia



Prominent U wave

  • The amplitude is> 1-2mm or > 25% T wave
  • The most common causes:
    - Bradycardia
    - Hypokalaemia
    - Uncommon causes
    - Hypocalcaemia
    - Hypomagnesemia
    - Hypothermia
    - Increased intracranial pressure
    - Left ventricular hypertrophy
    - Digoxin


Inverted U wave

  • It is highly specific for myocardial ischemia
  • It may be the first marker of acute coronary syndrome

  • Causes of inverted U wave
    - Myocardial ischemia
    - Cardiomyopathy
    - Hyperthyroidism



ECG 1 U wave in a patient with severe hypokalemia (best seen in V1-V3)


References

  1. Girish MP, Gupta MD, Mukhopadhyay S, Yusuf J, Sunil Roy TN, Trehan V. U wave: an important noninvasive electrocardiographic diagnostic marker. Indian Pacing Electrophysiol J. 2005 Jan 1;5(1):63-5. PMID: 16943944; PMCID: PMC1502069.
  2. https://www.techmed.sk/u-vlna/
  3. https://litfl.com/u-wave-ecg-library/