How to find the ECG axis
Other platforms explain it with text and video. In VMS you practice it on the patient.
The axis shows the main direction of the heart's electrical activity. An abnormal axis can point to conduction blocks, enlarged chambers or a lung problem.
Step by step
Look at lead I
Decide whether the QRS in lead I is mostly above (positive) or below (negative) the baseline. [1]
Look at lead aVF
Do the same for aVF. Together, leads I and aVF place the axis in one of four zones. [1]
Check lead II if needed
If lead I is positive and aVF is negative, look at lead II. Positive lead II means a normal axis; negative means left axis deviation. [1]
Refine with the flat lead
The limb lead where the QRS is most equally up and down is at right angles to the axis. [1]
Think of causes
Left axis deviation: left anterior fascicular block, LVH, inferior MI. Right axis deviation: right ventricle strain, pulmonary embolism, lateral MI, or normal in children and tall thin adults. [1]
Check the leads
A negative QRS and negative P wave in lead I often means the arm leads were swapped. Repeat the ECG before calling it abnormal. [2]
Common errors
- Calling left axis deviation when lead II is still positive.
- Missing reversed arm leads.
- Reading the axis from a single lead.
Quick axis method [1]
| Lead I | Lead aVF | Axis |
|---|---|---|
| Positive | Positive | Normal (0 to +90 degrees) |
| Positive | Negative | Check lead II: positive = normal (0 to -30), negative = left axis deviation |
| Negative | Positive | Right axis deviation (+90 to +180) |
| Negative | Negative | Extreme axis (-90 to 180) |
Practice it in VMS
In VMS you do this on the patient, not on paper: every step goes on the checklist with a score, and in Teach mode Blocky tells you what comes next.
VMS cases that train this skill
Sources
Facts and steps follow AAMC Core Entrustable Professional Activities (Core EPAs); NCCPA PANCE Content Blueprint. VMS is not affiliated with these organizations. Updated: 2026-10-11.