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QRS axis: Difference between revisions
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This indicates a normal heartaxis. Usually, these two leads are enough to diagnose a normal heartaxis! | This indicates a normal heartaxis. Usually, these two leads are enough to diagnose a normal heartaxis! | ||
The biggest vector in the heart is from the AV-node in the direction of the ventricular depolarization. Under normal | The biggest 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 heartaxis is between -30 and +90 degrees. | A normal heartaxis is between -30 and +90 degrees. | ||
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====Interpretation==== | ====Interpretation==== | ||
The interpretation of the electrical heartaxis 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. | ||
* | *Second, there are 4 quadrants where the QRS-vector can point to: | ||
** | **left upper quadrant --> left axis deviation (between -30º and -90º) | ||
** | **left lower quadrant --> normal (between -30º and 90º) | ||
** | **right below and right --> right axis deviation (between 90º and -150º) | ||
** | **right upper quadrant --> extreme axis (between -90º and -150º) | ||
'' | ''Example'': | ||
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. | |||
====Heart-axis Simulator==== | ====Heart-axis Simulator==== | ||
To understand how the ECG changes in axis deviations, this excellent axis-simulator may be helpful: http://www.blaufuss.org/ECGviewer/indexFrame2.html | |||
====Iso-electrical==== | ====Iso-electrical==== | ||
''' | '''Note:''' When the depolarization is perpendicular on the lead, this is called | ||
'''iso- | '''iso-electrical'''. The QRS is neither positive nor negative. | ||
====Undetermined axis ==== | ====Undetermined axis ==== | ||
When all extremity leads are biphasic, the axis is directed to the front or back, in a transverse plane. The axis is than '''undetermined'''. | |||
==Abnormal heartaxis== | |||
#In | [[Image:left_axis_dev.jpg|thumb| 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| 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]] | ||
# | 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 infracted 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. | |||
{{clr}} | {{clr}} | ||
==Examples of a left heartaxis== | ==Examples of a left heartaxis== | ||
[[Image:LHA.png|thumb| | [[Image:LHA.png|thumb| Left heartaxis]] | ||
[[Image:LAHB.png|thumb| | [[Image:LAHB.png|thumb| Left anterior hemi block]] | ||
*[[Conduction delay#LAFB| left anterior fascicular block]] | *[[Conduction delay#LAFB| left anterior fascicular block]] | ||
*[[Ischemia#Inferior|Inferior myocardial infarction]] | *[[Ischemia#Inferior|Inferior myocardial infarction]] | ||
*[[Hypertrophy|Left ventricular hypertrophy]] | *[[Hypertrophy|Left ventricular hypertrophy]] | ||
* | *Pacemaker rhythm | ||
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== Examples of a right heartaxis == | == Examples of a right heartaxis == | ||
[[Image:rightaxis.jpg|thumb| | [[Image:rightaxis.jpg|thumb| Right heartaxis]] | ||
*[[Hypertrophy| Right ventricular hypertrophy]] | *[[Hypertrophy| Right ventricular hypertrophy]] | ||
* | *Right ventricular load, for example [[Miscellaneous#Pulmonary_embolism|Pulmonary Embolism]] or Cor Pulmonale (as in COPD) | ||
*Atriumseptumdefect, | *Atriumseptumdefect, ventricleseptumdefect | ||
{{clr}} | {{clr}} | ||
<analytics uacct="UA-807577-6"></analytics> | <analytics uacct="UA-807577-6"></analytics> | ||