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Cardiovascular Research 2005 67(2):256-262; doi:10.1016/j.cardiores.2005.04.010
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Copyright © 2005, European Society of Cardiology

The U wave in the electrocardiogram: A solution for a 100-year-old riddle

Henk J. Ritsema van Eck*, Jan A. Kors and Gerard van Herpen

Department of Medical Informatics, Erasmus University Medical Center, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands

* Corresponding author. Tel.: +31 10 4088116; fax: +31 10 4089447. Email address: h.ritsemavaneck{at}erasmusmc.nl

Objective: In the electrocardiogram (ECG) the U wave follows the T, which is considered to reflect the repolarization of the cardiac ventricles. Despite the U wave's well-known clinical relevance, a satisfactory explanation of its origin is still outstanding. We have undertaken to explain the formation of the U wave by means of a simple digital model of the left ventricle.

Methods: The model employs a multi-layered segment of the myocardium. To each layer an action potential (AP) is assigned with shape and duration according to published data. The potential differences between the APs produce time-varying electrical sources. Each source contributes to the potentials in an arbitrary point P of the body. The strength of this contribution is determined by a specific coefficient, the "lead vector", linking P to the source. The ECG recorded at P is calculated as the sum of all potential contributions.

Results: The repolarization waves constructed in this way reproduce the natural aspects of a T wave followed by a U wave. The creation of a U wave is conditional on small voltage differences between the tail ends of the APs. No fundamental demarcation exists between U wave and preceding T wave. The morphology of the T–U wave is dependent on the geometrical position of P with respect to the myocardium.

Conclusion: T and U form a continuum. Together they are the resultant of one and the same process of repolarization of the ventricular myocardium. This has implications for the measurement of QT duration and for safety testing of drug-induced QT prolongation.

KEYWORDS ECG; Computer modeling; Membrane potential; Repolarization

Time for primary review 14 days


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