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ECG axis explanation and calculation
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This document was created by Alex Yartsev (dr.alex.yartsev@gmail.com); if I have used your data or images and forgot to reference you, please email me.The QRS Axis: the Isoelectric Lead Method
The AXIS is the chief direction of QRS propagation in the vaguely
coronal plane.
aVF
270 Left Axis To find the Axis in two steps, one must focus on the left side of the ECG
aVR aVL 1) Select the lead with the most isoelectric trace;
i.e. the lead in which Q and R waves are of the same height.
In the ECG above, that happens to be lead III.
180 0 Lead I The axis will be perpendicular to that lead orientation.
You need another lead to determine which direction the QRS is pointing in.
2) Select the lead which is perpendicular to the isoelectric lead
Right Axis This is the lead which will give you the direction.
Lead III Lead II
90 Normal Axis In this example, aVR is the perpendicular lead.
aVF If the QRS were predominantly upward in aVR, this would be extreme
270 right axis deviation.
aVR In the ECG above, the aVR is totally downward-facing.
aVL
This suggests a completely normal axis.
180 0 Lead I
Memorise The Perpendiculars:
- Lead I is perpendicular to aVF
- Lead II is perpendicular to aVL
Lead III Lead II - Lead I is perpendicular to aVR
90
aVF
270
aVR aVL
180 0 Lead I
Lead III 90 Lead II
From “the ECG made easy”, by Hampton (2003), and ECGs shamelessly stolen from Life in The Fastlane without any sort of permission, but in the non-commercial spirit of free education.
, This document was created by Alex Yartsev (dr.alex.yartsev@gmail.com); if I have used your data or images and forgot to reference you, please email me.
The QRS Axis: Quick Look Method
Gross deviations can be identified when you look at just 2 leads, aVF and Lead I
because aVF is perpendicular to lead I
If AVF is negative and Lead I is positive, look at Lead II.
270 Left Axis If Lead II is also negative, well its obviously a Left Axis
If Lead II is positive, it’s a vaguely leftish normal axis.
aVR aVL
Similarly, if Lead I is negative and AVF is negative,
180 0 Lead I While Lead III is positive, its still a right axis.
Yes, all of this adds additional unwanted steps
to this one-step method.
Right Axis
Lead III Lead II
Normal Axis
90
aVF
Normal Axis
- Lead I is POSITIVE
- aVF is POSITIVE
Left Axis
- Lead I is POSITIVE
- aVF is NEGATIVE
- Lead II is NEGATIVE
Right Axis
- Lead I is NEGATIVE
- aVF is POSITIVE
- Lead III is POSITIVE
No Mans Land
- Lead I is NEGATIVE
- aVF is NEGATIVE
The QRS Axis: The Quickest Look Method: just cheat, all’s fair in love and the ICU
The ECG machine will frequently print out the axis.
- Normal axis is -30 to 90.
- Left axis is anything more negative than -30
- Right axis is anything more positive than 90.
-
From “the ECG made easy”, by Hampton (2003), and ECGs shamelessly stolen from Life in The Fastlane without any sort of permission, but in the non-commercial spirit of free education.
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