QRS axis: Difference between revisions

11 bytes removed ,  16 January 2010
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[[Image:hart_axis.png|thumb]]
[[Image:hart_axis.png|thumb]]
<flashow>http://nl.ecgpedia.org/images/b/bc/Normal_SR_vector.swf|height=300px</flashow>
<flashow>http://nl.ecgpedia.org/images/b/bc/Normal_SR_vector.swf|height=300px</flashow>
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 heart axis. Especially a change of the heart axis or an extreme deviation can be an indication of pathology.
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 heart axis. A change of the heart axis or an extreme deviation can be an indication of 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 (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.
*Positive QRS deflection in lead AVF: the electrical activity is directed down.
This indicates a normal heart axis. Usually, these two leads are enough to diagnose a normal heart axis!
This indicates a normal heart axis. Usually, these two leads are enough to diagnose a normal heart axis!


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.
The largest vector in the heart is from the AV-node in the direction of 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. In the middle of the figure is the AV-node. A horizontal line towards the left arm is defined as 0 degrees.


A normal heart axis is between -30 and +90 degrees.
A normal heart axis is between -30 and +90 degrees.
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====Interpretation====
====Interpretation====
The interpretation of the electrical heartaxis has a few rules of thumb:
The interpretation of the electrical heart axis has a few rules of thumb:


* First, when a positive depolarization wave moves towards a positive electrode, a positive, upwards deflection is registered on the ECG.
* First, when a positive depolarization wave moves towards a positive electrode, a positive, upwards deflection is registered on the ECG.
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