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QRS axis: Difference between revisions
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For a lot of people, this is a difficult concept. The theoretical part seems difficult but by | For a lot of people, this is a difficult concept. The theoretical part seems difficult, but by working with it a lot, the reader will find it becoming clear. | ||
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{{clr}} | {{clr}} | ||
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* 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. | ||
*Second, there are 4 quadrants where the QRS-vector can point | *Second, there are 4 quadrants where the QRS-vector can point: | ||
**left upper quadrant --> left axis deviation (between -30º and -90º) | **left upper quadrant --> left axis deviation (between -30º and -90º) | ||
**left lower quadrant --> normal (between -30º and 90º) | **left lower quadrant --> normal (between -30º and 90º) | ||
**right | **right lower quadrant --> right axis deviation (between 90º and -150º) | ||
**right upper quadrant --> extreme axis (between -90º and -150º) | **right upper quadrant --> extreme axis (between -90º and -150º) | ||
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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. | 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. | ||
;Iso- | ;Iso-electric | ||
:When the depolarization is perpendicular on the lead, this is called '''iso- | :When the depolarization is perpendicular on the lead, this is called '''iso-electric'''. The QRS is neither positive nor negative. | ||
;Undetermined axis | ;Undetermined axis | ||
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<div style="float:right"> | <div style="float:right"> | ||
<gallery> | <gallery> | ||
Image:left_axis_dev.jpg| | Image:left_axis_dev.jpg| Heart axis deviation to the left in case of an inferior infarct. Left anterior hemiblock is a common cause. A left axis is between -30 and -90 degrees. The axis is -30 degrees. | ||
Image:right_axis_dev.jpg| | Image:right_axis_dev.jpg| Heart axis 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 | ||
</gallery> | </gallery> | ||
</div> | </div> | ||
The direction of the vector can changes | 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. | #When the heart itself is rotated (right ventricular overload), obviously the axis turns with it. | ||
#In case of ventricular hypertrophy, the axis will deviate | #In case of ventricular hypertrophy, the axis will deviate toward the greater electrical activity and the vector will turn toward the hypertrophied tissue. | ||
#Infarcted tissue is electrically dead. No electrical activity is registered and the QRS vector turns away from the infarcted 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 | #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 in RBBB only the right ventricle determines the vector. | ||
{{clr}} | {{clr}} | ||
==Left axis deviation== | ==Left axis deviation== | ||
[[Image:LHA.png|thumb| Left | [[Image:LHA.png|thumb| Left heart axis]] | ||
[[Image:LAHB.png|thumb| Left anterior | [[Image:LAHB.png|thumb| Left anterior hemiblock]] | ||
Causes of left axis deviation include: | Causes of left axis deviation include: | ||
*Normal variation (physiologic, often with age) | *Normal variation (physiologic, often with age) | ||