The U wave

• The U wave is found after the T wave.

• Begins from baseline after the end of T wave.

• It was first described by Einthoven in the year (1903).

• Its amplitude is 0.33mV or 11% of the T wave and has the same polarity as the T wave.

• The U wave represents the end of repolarization and is best seen in the precordial leads V2-V3.

• The U wave is rarely seen in 50-75% of cases.

• It is heart rate dependent, 90% of cases with HR below 65 bpm and rarely found with HR above 95 bpm.

Arrows depict U waves on leads V3 - V4

Origin of the U wave

Several theories have been postulated regarding the origin of the U wave but it is still controversial. Some theories include

• Delayed afterdepolarization of the His-Purkinje system

• Repolarization of the papillary muscle

• Prolonged repolarization in the mid myocardium cells (M cells)

Prominent U wave

Can be seen on several instances including

• Hypokalemia

• Class Ia and III antiarrhythmics

• LQTS

• Bradycardia

• Hypothermia

• Left ventricular hypertrophy

• Normal variant

Negative U waves

Negative U waves have been associated with heart disease specifically

• Myocardial ischemia

• Myocardial infarction

• Ventricular hypertrophy

• Valvular disease

• Hypertension.

References

1. AHA/ACCF/HRS Recommendations for the Standardization and Interpretation

   of the Electrocardiogram Part IV: The ST Segment, T and U Waves, and the QT Interval

2. Cardiovasc Metab Sci. 2021; 32(4): 197 - 205

3. Surawicz B. U wave: Facts, hypotheses, misconceptions, and misnomers. J Cardiovasc Electrophysiol. 1998; 9 (10): 1117-1128.

4. Duque-González L, Gaviria-Aguilar MC, Lopera-Mejía L, Duque-Ramírez M. The U wave: an ignored wave flled with

   information. Cardiovasc Metab Sci. 2021; 32 (4): 197-205.

5. Carrillo-Esper R, et al. The U wave in the electrocardiogram. More than an academic curiosity. Rev Invest Med Sur Mex, 2015; 22 (1): 27-29