INFLUENCE OF LEAD SELECTION AND POPULATION ON AUTOMATED MEASUREMENT OF QT DISPERSION

Background-The study of QT dispersion (QTd) is of increasing clinical interest, but there are very few data in large healthy populations. Fu rthermore, there is still discussion on the extent to which QTd reflec ts dispersion of measurement. This study addresses these problems. Met hods and Results-Twelve-lead ECGs recorded on 1501 apparently healthy adults and 1784 healthy neonates, infants, and children were used to d erive normal limits of QTd and QT intervals by use of a fully automate d approach. No age gradient or sex differences in QTd were seen and it was found that an upper limit of 50 ms was highly specific. Three-ort hogonal-lead ECGs (n = 1220) from the Common Standards for Quantitativ e Electrocardiography database were used to generate derived 12-lead E CGs, which had a significant increase in QTd of 10.1+/-13.1 ms compare d with the original orthogonal-lead ECG but a mean difference of only 1.63+/-12.2 ms compared with the original 12-lead ECGs. In a populatio n of 361 patients with old myocardial infarction, there was a statisti cally significant increase in mean QTd compared with that of the adult normal group (32.7+/-10.0 versus 24.53+/-8.2 ms; P<0.0001). An estima te of computer measurement error was also obtained by creating 2 sets of 1220 ECCs from the original set of 1220, The mean error (difference in QTd on a paired basis) was found to be 0.28+/-9.7 ms. Conclusions- These data indicate that QTd is age and sex independent, has a highly specific upper normal limit of 50 ms, is significantly lower in the 3- orthogonal-lead than in the 12-lead EGG, and is longer in patients wit h a previous myocardial infarction than in normal subjects.