Dispersion of ventricular repolarization: reality? Illusion? Significance?

The QT interval is considered to be a surrogate of cellular action potential duration. However, it yields a limited view of the complex electrogenesis of the ventricular repolarization (VR). Evidence of T-wave end inequality among surface ECG traces back to Wilson et al,1 and it was recently revived by the concept of dispersion.2 Because of its apparent simplicity, QT dispersion became fashionable, and a growing literature is now devoted to its potential prognostic interest. The study by Zabel et al3 seems timely to temper the enthusiasm. In a prospectively collected cohort of patients, it offers evidence that avoiding technical biases of measurement, QT dispersion is not a prognostic marker. This contrasts with the confirmation that ejection fraction, heart rate variability, and simply heart rate are indeed good predictors of events. It suggests some reflections about the correct and comprehensive use of a concept that still needs to be validated. ### Measurement of QT Duration QT interval can be measured manually or with dedicated algorithms. The performances of the 2 approaches were compared in a remarkable study conducted by the late Jos Willems.4 The aim was to assess the diagnostic performances of computerized systems.5 In view of the interobserver and intraobserver variability in determining wave recognition points, an elaborate reviewing scheme was devised to obtain a group estimate that should define the “truth,” ultimately serving as a standard for computer measurement. Five experts defined individually the P- and QRS-wave onset and offset and the T-wave offset. The database was formed of 250 digitized (500 Hz) 12 standard leads and Frank XYZ leads, including a 25% proportion of normal hearts and a variety of ventricular hypertrophies and infarctions but no bundle-branch block or long-QT syndrome. The interexpert variation was expressed as 2 SD of the difference between the median and the individual …