QT dispersion is measured as the difference between the maximal and minimal QT intervals.6,9–10 While the definition is straightforward, its accurate measurement becomes quite complex. First determining the end of the T wave can often be difficult, particularly if the T wave is of relatively low amplitude. Five “experts” were asked to measure the onset of the QRS complex and the end of the T wave in 250 ECGs from both normal and abnormal hearts without QT interval prolongation or bundle-branch block.11The interexpert variation for the QRS onset was 6.5 ms, but the variation for the end of the T wave was 30.6 ms with an intraindividual variability of 8 ms. Several computer algorithms have been developed to accurately and reproducibly localize the end of the T wave, but have not been associated with any significant improvement in reproducibility over manual techniques.12–13 Unfortunately, increasing paper speed or amplifying the signals do not aid in measuring the T wave end point.14 In general, interobserver and intraobserver variability of QT dispersion measurements can be as much as 30 to 40%.9,15Second, it is not clear whether QT dispersion measurements must be corrected for rate. Several large studies16–17 have demonstrated the potential clinical utility of QTc dispersion, but a recent clinical study18 in 35 patients demonstrated that QT dispersion is independent of heart rate. Since elevated heart rate itself is associated with increased risk of death in the general population, analysis of QT dispersion should probably not be rate corrected to eliminate the influence from an additional variable.18–19 Third, the specific number of leads required for measurement of QT dispersion has not been formally defined. Initial studies in QT dispersion used body surface potential mapping (BSPM) with 100 to 200 unipolar precordial ECGs to identify differences in ventricular repolarization. A subsequent study by Cowan et al10 found that the values obtained from the surface 12-lead ECG were similar to those obtained by BSPM. However, since only two of the six frontal plane leads are actually recorded while the other four are derived mathematically, many clinical studies have used only six unipolar precordial leads or eight leads (two frontal plane leads and six precordial leads). The T wave generally shortens and decreases in amplitude from precordial leads V2 to V6 to reach minimal values in aVL due to tissue attenuation from air in the lungs. Recent studies suggest that using a specific combination of “quasiorthogonal” leads (aVF, V1, and V4; I, aVF, V2, and V4) may provide sufficient QT dispersion data for analysis.,20 However, at this time no standardized method for acquiring QT dispersion exists.