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QRS axis: Difference between revisions
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<flashow>http://nl.ecgpedia.org/images/c/cc/ | <flashow>http://nl.ecgpedia.org/images/c/cc/Heart axis.swf|height=350px|width=600px</flashow> | ||
'''''Click and drag the arrow in the above animation to change the heart axis and see how the ECG changes.''''' | '''''Click and drag the arrow in the above animation to change the heart axis and see how the ECG changes.''''' | ||
The electrical | The electrical heart axis 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 | 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. | ||
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==How do you determine the electrical | ==How do you determine the electrical heart axis== | ||
[[Image:ECG_lead_angulation.png|300px|left]] | [[Image:ECG_lead_angulation.png|300px|left]] | ||
[[Image:hartas2.jpg|thumb|The | [[Image:hartas2.jpg|thumb|The heart axis indicates the average direction of the depolarization wave. A normal heart axis, the picture shows an example, is between -30 and +90 degrees. In this example, the heart axis is +45 degrees.]] | ||
[[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 | 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 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 (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 | 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 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. | ||
A normal | A normal heart axis is between -30 and +90 degrees. | ||
'''Rule:''' biggest QRS deflection in I and II is an intermediate = normal | '''Rule:''' biggest QRS deflection in I and II is an intermediate = normal heart axis. | ||
So positive deflections in I and II indicates a normal | So positive deflections in I and II indicates a normal heart axis. | ||
====Interpretation==== | ====Interpretation==== | ||
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==Abnormal | ==Abnormal heart axis== | ||
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