Origin on the electrocardiogram of U-waves and abnormal U-wave inversion

AIMS: Soon after the initial development of electrocardiography, U-waves were discovered in many normal subjects following the T-wave repolarisation waveform on the electrocardiogram. Various explanations have been offered for their origin, but none is universally accepted. We used our model of left ventricular repolarisation to explore the most common hypotheses for the genesis of U-waves. METHODS: Recently, we have shown that a computer model of left ventricular repolarisation was able to explain the formation of the characteristic shape of the T-wave, and we have now used this model to explore the most common hypotheses for the genesis of U-waves. The repolarisation phase of the action potentials in the model exhibited an after-potential. We investigated separately the effect on the 12-lead electrocardiogram of three different features of the model: the amplitude of the after-potential; dispersion of repolarisation in the left ventricle ranging from 20 to 100 ms; the timing of the after-potential, relative to the end of the principal action potential component, ranging from -100 to 100 ms. RESULTS: We show that delaying repolarisation in different regions of the heart cannot explain the U-wave, but show that the presence of after-potentials on the cardiac action potential do explain the U-wave polarity and other characteristic U-wave features. We also show that abnormal after-potential timing corresponds with abnormal U-wave inversion. CONCLUSION: Our model provides a realistic and simple solution to the problem of U-wave genesis.