Electrocardiography: the electrical axis.

The term "electrical axis of the heart" as conventionally used refers to the mean frontal-plane axis of the QRS complex. It is defined as the angle between the mean QRS vector and lead I and can be determined to the nearest 15 degrees by simple inspection of the frontal-plane leads. The axis is related to age and body build and deviates significantly from normal in various disease states. There are two common causes of abnormal LAD and several common causes of abnormal RAD.