QT and Dispersion of Ventricular Repolarization: The Greatest Fallacy in Electrocardiography in the 1990s
To The Editor:
The recent, most thoughtful editorial authored by Coumel et al,1 commenting on the article by Zabel et al,2 is likely to create a great deal of interest and perhaps also some controversy. The arguments presented challenge the prevailing interpretation of the meaning of QT dispersion.
As the authors point out, there is only 1 end of repolarization in body surface ECGs, generated by source events in the myocardial region repolarizing last. This argument holds because there are no significant nondipolar components during repolarization in surface ECG leads. The apparent QT dispersion is due to differing spatial orientation of the ECG lead vectors and their differing sensitivity, which modifies T-wave amplitudes even if the projections of cardiac vectors on them are identical otherwise. For true dispersion of repolarization, we also need to consider the onset of ventricular repolarization. In local epicardial electrograms, the best estimate of this time point is the maximum of the first time derivative,3 near T-wave peak. This is not at the end of the T wave in body surface leads. Exactly where it is remains to be seen. Has all this work on dispersion of repolarization focused on the wrong measurement?
Information about abnormal repolarization can be more readily extracted in the amplitude rather than time domain of the T wave. QT dispersion, as measured presently, does not relate to any electrophysiologically meaningful source events.
Indeed, the prevailing interpretation of QT dispersion seems to have an element of a great fallacy. Is this at least in part because our young generation of electrocardiographers is no longer adequately exposed to elementary concepts of vectorcardiography?
- Copyright © 1999 by American Heart Association
Coumel P, Maison-Blanche P, Badilini F. Dispersion of ventricular repolarization: reality? illusion? significance? Circulation. 1998;97:2491–2493.
Zabel M, Klingenheben T, Franz MR, Hohnloser SH. Assessment of QT dispersion for prediction of mortality or arrhythmic events after myocardial infarction: results of a prospective, long-term follow-up study. Circulation. 1998;97:2543–2550.
Lux RL, Fuller MS, Macleod RS, Ersler PR, Green LS, Taccardi B. QT dispersion: dispersion of ventricular repolarization or dispersion of the QT interval? J Electrocardiol. 1997;30(suppl):176–180.