Relationship between QT interval and ventricular electrical axis: A new suggestion for Lead selection in QT interval measurement

Abstract

Exploration of the interlead QT variation (QT dispersion) introduced cardiologists to some new concepts including the deed to define a standard for lead selection in the measurement of QT interval and the reason or factors contributing to QT dispersion. Hoseever, still there dose not exist a generally acceptable standard for lead selection and the reason for the QT dispersion has not been given the importance it deserves. Only a few hypotheses have been suggested, none of which have been seriously experimented. Finding important factors cuusing QT dispersion can lead to a better understanding of its basics and more accurate usage of QT dispersion as and index in clinical practice. This paper examines the "Vector Cancellation Theory" on the basis that if "vector cancellation" affects the QT interval duration in different leads, the ncurest had to rhe mean QR.S axis must have the longest QT interval and vice versa. This was tested on the electrocardiograms taken from 34 people without cardiovascular problems. We came across a statistically significant inverse correlation between the QT interval in each limb lead and its angle to the ECG's mean QRS axis. Thus this study gives weight to the vector cancellation theory. And as the nearest lead to the Mean QRS Axis is likely to have the longest QT interval and given its practicality. It can be suggested as the standard lead for measuring QT internal in an electrocardiogram.