Electrical axis of the heart

Atrial activation is depicted by the P wave vector and ventricular activation by the QRS vector. The ventricular activation has an initial, middle and terminal component. The mean ventricular electrical activity is represented by the mean electrical axis of the QRS. QRS vector can be assessed in multiple planes: horizontal, saggittal and frontal. T wave vector can also be assessed. The relation between the T wave vector and the QRS vector is termed the ventricular gradient. Normal QRS axis in the frontal plane is roughly between 0 – 90 degrees.