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QRS axis: Difference between revisions
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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. | 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 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 | 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. | ||