'''''Click and drag the arrow in the above animation to change the heart axis and see how the ECG changes.'''''
heartaxis is an average of all depolarizations in the heart. The depolarization wave begins in the right atrium and proceeds to the left and right ventricle. Because the left ventricle wall is thicker than the right wall, the arrow indicating the direction of the depolarization wave is directed to the left.
For a lot of people, this is a difficult concept. The
theoretic part seems difficult but by doing it a lot, it will become clear.
==How do you determine the electrical
heartaxis indicates the average direction of the depolarization wave. A normal heartaxis, the picture shows an example, is between -30 and +90 degrees. In this example, the heartaxis is +45 degrees.]]
When you average all electrical signals from the heart, you can indicate the direction of the average electrical depolarization with an arrow (vector). This is the
heartaxis. Especially a change of the heartaxis or an extreme deviation can be an indication for pathology.
*Positive (the average of the QRS surface above the baseline) QRS deflection in lead I: the electrical activity is directed to the left (of the patient)
*Positive QRS deflection in lead AVF: the electrical activity is directed down.
This indicates a normal
heartaxis. Usually, these two leads are enough to diagnose a normal heartaxis!
The largest vector in the heart is from the AV-node in the direction of the ventricular depolarization. Under normal circumstances, this is directed left and down.(towards leads I and AVF). The position of the QRS vector is given in degrees. See the figure, the middle of the figure is the AV-node. A horizontal line towards the left arm is defined as 0 degrees.
heartaxis is between -30 and +90 degrees.
'''Rule:''' biggest QRS deflection in I and II is an intermediate = normal
heartaxis. So positive deflections in I and II indicates a normal heartaxis.