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(Circulation. 1999;99:1458-1463.)
© 1999 American Heart Association, Inc.

Clinical Investigation and Reports

QT Dispersion as an Attribute of T-Loop Morphology

Jan A. Kors, PhD; Gerard van Herpen, MD, PhD; Jan H. van Bemmel, PhD

From the Department of Medical Informatics, Faculty of Medicine and Health Sciences, Erasmus University, Rotterdam, the Netherlands.

Correspondence to J.A. Kors, PhD, Department of Medical Informatics, Faculty of Medicine and Health Sciences, Erasmus University, PO Box 1738, 3000 DR Rotterdam, Netherlands. E-mail kors{at}mi.fgg.eur.nl

Background—The suggestion that increased QT dispersion (QTD) is due to increased differences in local action potential durations within the myocardium is wanting. An alternative explanation was sought by relating QTD to vectorcardiographic 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 second halves of the loop). We reasoned that small, wide ("pathological") T loops produce larger QTD than large, narrow ("normal") loops. To quantify the relationship between QTD and T-loop morphology, we used a program for automated analysis of ECGs and a database of 1220 standard simultaneous 12-lead ECGs. For each ECG, QT durations, QTD, and T-loop parameters were computed. T-loop amplitude and width were dichotomized, with 250 µV (small versus large amplitudes) and 30° (narrow versus wide loops) taken as thresholds. 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<0.001).

Conclusions—QTD is an attribute of T-loop morphology, as expressed by T-loop amplitude and width.

Key Words: electrocardiography • computers • potentials

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