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For a lot of people, this is a difficult concept. The theoretical part seems difficult but by
doing it a lot, the reader will find it becoming clear.
* First, when a positive depolarization wave moves towards a positive electrode, a positive, upwards deflection is registered on the ECG.
*Second, there are 4 quadrants where the QRS-vector can point
**left upper quadrant --> left axis deviation (between -30º and -90º)
**left lower quadrant --> normal (between -30º and 90º)
below and right --> right axis deviation (between 90º and -150º)
**right upper quadrant --> extreme axis (between -90º and -150º)
The QRS in lead I, will have a negative deflection in a right axis deviation. The vector is not directed towards the electrode. However, lead AVF will be positive, the vector is directed towards the electrode.
electrical:When the depolarization is perpendicular on the lead, this is called '''iso- electrical'''. The QRS is neither positive nor negative.
Heartaxis deviation to the left in case of an inferior infarct. Left anterior hemi Block is a common cause. A left axis is between -30 and -90 degrees. The axis is -30 degrees.Image:right_axis_dev.jpg| Heartaxis deviation to the right in right ventricular load, as in COPD or pulmonary embolism. A right axis is between +90 and +180 degrees. In this case the axis is +135 degrees
The direction of the vector can changes
under different circumstances:
#When the heart itself is rotated (right ventricular overload), obviously the axis turns with it.
#In case of ventricular hypertrophy, the axis will deviate
by the bigger electrical activity and the vector will turn towards the hypertrophied tissue.
#Infarcted tissue is electrically dead. No electrical activity is registered and the QRS vector turns away from the infarcted tissue
#In conduction problems, the axis deviates too. When the right ventricle depolarizes later than the left ventricle, the axis will turn to the right (RBBB). This is because the right ventricle will begin the contraction later and therefore will also finish later. In a normal situation the vector is influenced by the left ventricle but
now only by the right ventricle.
==Left axis deviation==
heartaxis]][[Image:LAHB.png|thumb| Left anterior hemi block]]
Causes of left axis deviation include:
*Normal variation (physiologic, often with age)