Axis: Bold As Love
Axis determination is one of the most common ECG topics that I see junior doctors (and some senior doctors!) struggling with. Hopefully this tutorial will clear things up…
ECG Axis Determination
The diagram below illustrates the relationship between QRS axis and the frontal leads of the ECG.
Image reproduced from Chung
Normal Axis = QRS axis between -30 and +90 degrees.
Left Axis Deviation = QRS axis less than -30 degrees.
Right Axis Deviation = QRS axis greater than +90 degrees.
Extreme Axis Deviation = QRS axis between -90 and 180 degrees (AKA “Northwest Axis”).
There are several complementary approaches to estimating QRS axis, which are summarised below.
Method 1 – The Quadrant Method
The most efficient way to estimate axis is to look at leads I + aVF.
Lead ILead aVFQuadrantAxis
PositivePositiveLeft lower quadrantNormal (0 to +90 degrees)
PositiveNegativeLeft upper quadrantPossible LAD (0 to -90 degrees)
NegativePositiveRight lower quadrantRAD (+90 to 180 degrees)
NegativeNegativeRight upper quadrantExtreme Axis Deviation (-90 to 180 degrees)
Method 2 – Leads I + II
Another rapid method is to look at leads I + II.
A positive QRS in lead I puts the axis in roughly the same direction as lead I.
Image reproduced from Chung
A positive QRS in lead II similarly aligns the axis with lead II.
Image reproduced from Chung
Therefore, if leads I and II are both positive, the axis is between -30...
Source: Life in the Fast Lane - Category: Emergency Medicine Authors: Edward Burns Tags: Cardiology ECG Emergency Medicine axis deviation EKG LAD rad Source Type: blogs