Axis Deviation

The axis on an EKG is best determined by looking at the direction of the QRS complex in leads I and aVF. It is important to remember how all of the limb leads are oriented, though, as it is not always completely clear by these leads alone.

QRS complexes in lead I that are more positive than negative will be on the right part of the hexaxial reference system. QRS complexes that are more positive in lead aVF will be on the bottom half. If the QRS complex is more positive than negative in both of those leads, the QRS axis is normal. If the lead is isoelectric, then the axis is 90* to that lead (isoelectric lead in I means either a +90* or -90*. The above hexaxial reference system nicely displays the directionality of all limb leads and is worth memorizing.

Normal Axis

The normal axis is between -30* and +90*. Using the quadrant method that is described above, this is most easily determined when lead I is positive and lead aVF is positive or mostly positive.

Using the quadrant method, this EKG is normal axis. Using the more specific hexaxial reference with multiple leads, one can figure out that this is +60*. Specifically, aVL is isoelectric, so it must be 90* off from -30*. Additionally, lead II is completely positive, pointing towards +60*.