Axis deviation

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ECG Axis Interpretation

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 I	LEAD AVF	QUADRANT	AXIS
Positive	Positive	Left lower quadrant	Normal (0 to +90 degrees)
Positive	Negative	Left upper quadrant	Possible LAD (0 to -90 degrees)
Negative	Positive	Right lower quadrant	RAD (+90 to 180 degrees)
Negative	Negative	Right upper quadrant	Extreme Axis Deviation (-90 to 180 degrees)