QT dispersion as an attribute of T-loop morphology

Background-The suggestion that increased QT dispersion (QTD) is due to incr eased differences in local action potential durations within the myocardium is wanting. An alternative explanation was sought by relating QTD to vecto rcardiographic T-loop morphology. Methods and Results-The T loop is characterized by its amplitude and width (defined as the spatial angle between the mean vectors of the first and sec ond halves of-the loop). We reasoned that small, wide ("pathological") T lo ops produce larger QTD than large, narrow ("normal") loops. To quantify the relationship between QTD and T-loop morphology, we used a program for auto mated analysis of ECGs and a database of 1220 standard simultaneous 12-lead ECGs. For each EGG, QT durations, QTD, and T-loop parameters were computed . T-loop amplitude and width were dichotomized, with 250 mu V (small versus large amplitudes) and 30 degrees (narrow versus wide loops) taken as thres holds. Over all 1220 ECGs, QTDs were smallest for large, narrow T loops (54 .2 +/- 27.1 ms) and largest for small, wide loops (69.5 +/- 33.5 ms; P<0.00 1). Conclusions-QTD is an attribute of T-loop morphology, as expressed by T-loo p amplitude and width.