The Electrical Axis Made Simple
Determining the cardiac electrical axis can seem intimidating, but there's a simple method that takes only seconds.
The DI + aVF Method
You only need two leads: DI and aVF.
| DI | aVF | Axis |
|---|---|---|
| ↑ Positive | ↑ Positive | Normal (0° to +90°) |
| ↑ Positive | ↓ Negative | Left axis deviation (-30° to -90°) |
| ↓ Negative | ↑ Positive | Right axis deviation (+90° to +180°) |
| ↓ Negative | ↓ Negative | Extreme (-90° to -180°) |
Step by Step
1. Look at DI: Is the QRS predominantly positive or negative?
2. Look at aVF: Is the QRS predominantly positive or negative?
3. Check the table above
Refining the Axis
For greater precision, find the most isoelectric lead (QRS with equal amplitude of positive and negative components). The axis will be perpendicular to this lead.
Causes of Axis Deviation
Left axis deviation:
- Left anterior fascicular block (LAFB)
- Left ventricular hypertrophy
- Inferior infarction
Right axis deviation:
- Left posterior fascicular block (LPFB)
- Right ventricular hypertrophy
- COPD
- Pulmonary embolism
Practical Tip
In the QTc app, after calibrating the image, you can analyze the QRS complex in different leads to quickly determine the axis.
Practice this method on the next 10 ECGs you analyze and it will become automatic!
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