Orthogonal leads for the measurement of QT dispersion: a comparison with conventional leads.

To determine the characteristics of QT interval dispersion using orthogonal ECG leads with high paper speed (100 mm/s) and high voltage gain (10 cm/mV) as compared to conventional 12-lead ECG, we measured the QT dispersion in 57 patients at rest and directly after exercise using these two techniques. The measurements were repeated by the same observer and by an independent observer in 29 patients to assess reproducibility. QT dispersion was found to be significantly lower in orthogonal leads than standard lead tracings (24+/-20 ms versus 44+/-17 ms at rest, P<0.001; 29+/-21 ms versus 53+/-27 ms after exercise, P<0.001, respectively). The intrasubject and interobserver reproducibility was better for the orthogonal lead tracings, making this technique a potentially useful tool for future research.