==How do you determine the electrical heartaxis==
[[Image:hartas2.jpg|thumb|The 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.]]
|200px|Heartaxis from the original publication of Einthoven. Reprinted from The Lancet, March 30 1912, Einthoven W., ''The Different Forms of The Human Electrocardiogram and Their Signification'', 853-861, 1912, with permission from Elsevier]]
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.
:When all extremity leads are biphasic, the axis is directed to the front or back, in a transverse plane. The axis is than '''undetermined'''.
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.
[[Image:left_axis_dev.jpg|thumb|left| 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|thumb|none| 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]]
==Left axis deviation==
[[Image:LHA.png|thumb| Left heartaxis]]
*Right ventricular load, for example [[Pulmonary_Embolism|Pulmonary Embolism]] or Cor Pulmonale (as in COPD)