ABSTRACT
Together, aVR, aVL, aVF, I, II, and III provide a ‘clock face’ view of cardiac electrical activity in the frontal plane of the body (Figure 47.4) and can be used to assess the direction of the mean frontal cardiac axis. (They say nothing about electrical vector activity at right angles to the coronal plane.) The cardiac axis is the direction of the mean electrical vector which results from all the individual cellular depolarizations during the production of the QRS. It is therefore in the approximate direction of the lead with the tallest R wave or at right angles to the lead in which the R and S waves are equal. There are only six leads available for assessment and the axis can therefore only be obtained to the nearest 30° on visual inspection. This means that firm statements can be made only when the axis deviation is considerable.
