The frontal plane QRS-T angle

Abstract

This editorial refers to ‘QRS-T angle as a predictor of sudden cardiac death in a middle-aged general population’ by A.L. Aro et al ., on page 872 Availability of the limb leads of the 12-lead electrocardiogram (ECG) allows calculation of a mean QRS axis and a mean T axis, as is well known. These axes lie in the frontal plane of the body and can be used to calculate a very simple difference in angle between the two axes, namely the planar QRS-T axis. In contrast, it is possible to calculate the mean direction of ventricular activation in three-dimensional space. This is sometimes termed the orientation of the mean spatial QRS vector. Similarly, there is a mean spatial T vector and the science of vectorcardiography revolves around the study of spatial P, QRS, and T vectors as they vary throughout the cardiac cycle.1 Figure 1 shows a mean spatial QRS and T vector and their corresponding projections onto the frontal plane. Figure 1 The illustration shows a spatial QRS vector QRSsp and a spatial T vector Tsp projected onto the frontal plane to give a frontal plane T axis denoted Tf and a frontal plane QRS axis denoted QRSf. The angle between the frontal plane QRS and T vectors is denoted with ‘a’ whereas the shaded angle between the spatial QRS and T vectors is denoted with ‘b’. QRSf and Tf are derived, in this case, from spatial vectors whereas the frontal plane QRS and T axes are usually derived from the limb leads of the 12-lead electrocardiogram. However, the illustration shows how there potentially can be large differences between the spatial QRS-T angle and the frontal plane QRS-T angle. The axes are labelled I, aVF, and V2 for ease of linking the frontal plane vectors with the concept of spatial vectors, …