QRS Axis Interpretation: Positive in I and II, Negative in aVF
No, this is NOT a leftward axis—this pattern represents a normal axis between 0° and +60°. A leftward (left axis deviation) requires the axis to be between -30° and -90°, which would show a positive QRS in lead I but a negative QRS in lead II 1.
Understanding the Axis Quadrant System
The frontal plane axis is determined by analyzing QRS polarity in leads I and aVF, which are orthogonal (perpendicular) to each other in the hexaxial system 2:
- Lead I at 0°: Positive QRS indicates axis is leftward (between -90° and +90°)
- Lead aVF at +90°: Positive QRS indicates axis is inferior (between 0° and +180°)
Your Specific Pattern Analysis
With positive QRS in leads I and II, but negative in aVF, the axis falls in the normal range between 0° and +60° 2:
- Positive lead I: Confirms the axis is somewhere between -90° and +90°
- Positive lead II (at +60°): Indicates the axis has not deviated leftward past 0°
- Negative lead aVF (at +90°): Indicates the axis is superior to +90°, narrowing the range to between 0° and +90°
Since lead II is positive, the axis must be between 0° and +60° (closer to lead II's orientation) 2.
Defining Left Axis Deviation
True left axis deviation requires the frontal plane axis to be between -45° and -90° 3, 1. The key distinguishing features are:
- Positive QRS in lead I (present in your case)
- Negative QRS in lead II (NOT present in your case—this is the critical difference)
- Negative QRS in lead aVF (present in your case, but insufficient alone)
Common Clinical Pitfall
The most frequent error is assuming that a negative aVF alone indicates left axis deviation 2. Lead II polarity is the critical discriminator:
- If lead II is positive with negative aVF → Normal axis (0° to +60°)
- If lead II is negative with negative aVF → Left axis deviation (-30° to -90°) 1
When Left Axis Deviation Matters Clinically
Left axis deviation between -45° and -90° suggests left anterior fascicular block (LAFB) when accompanied by 3, 1:
- QRS duration <120 ms
- qR pattern in lead aVL
- R-peak time in aVL ≥45 ms
- rS pattern in leads II, III, and aVF
However, your pattern does not meet these criteria since lead II is positive 1.