How to Assess for Axis Deviation on EKG
To assess for axis deviation on an EKG, examine leads I and aVF: if both are positive, the axis is normal; if I is positive and aVF negative, left axis deviation exists; if I is negative and aVF positive, right axis deviation exists; and if both are negative, extreme right axis deviation is present. 1
Normal Axis Ranges by Age
Understanding normal axis ranges by age is essential for proper interpretation:
- Adults: +30° to +90° 1
- Children 8-16 years: up to +120° 2, 1
- Children 5-8 years: up to +140° 2, 1
- Children 1-5 years: +10° to +110° 2, 1
- Neonates: +30° to +190° 1
Step-by-Step Assessment Method
1. Determine if QRS is Predominantly Positive or Negative in Key Leads
- Lead I: Represents 0° on the hexaxial reference system
- Lead aVF: Represents +90° on the hexaxial reference system
2. Apply the Quadrant Method
Based on the polarity of leads I and aVF, determine which quadrant the axis falls into:
| Lead I | Lead aVF | Axis Interpretation |
|---|---|---|
| Positive | Positive | Normal axis (0° to +90°) |
| Positive | Negative | Left axis deviation (-1° to -90°) |
| Negative | Positive | Right axis deviation (+91° to +180°) |
| Negative | Negative | Extreme right axis deviation (+181° to -91°) |
3. Refine the Axis Calculation
For more precise determination:
- Find the most isoelectric limb lead (where QRS complex is most equiphasic)
- The axis is perpendicular to this lead
- Use the quadrant determined above to identify the correct perpendicular direction
If the QRS complex is equiphasic in all leads, the axis is considered indeterminate 2.
Identifying Specific Axis Deviations
Left Axis Deviation (LAD)
- Definition: Mean frontal plane QRS axis of -30° or more leftward in adults 1
- Associated findings: Often seen with left anterior fascicular block, which has specific criteria:
- Frontal plane axis between -45° and -90° 2
- qR pattern in lead aVL
- R-peak time in lead aVL of 45 ms or more
- QRS duration less than 120 ms
Right Axis Deviation (RAD)
- Definition: Mean frontal plane QRS axis greater than +90° in adults
- Common causes: Right ventricular hypertrophy, lateral wall MI, left posterior fascicular block
Extreme Axis Deviation
- Definition: Axis beyond +180° or approaching -90°
- Clinical significance: Often indicates severe cardiac pathology
Common Pitfalls and Caveats
Lead Misplacement: Limb lead reversals can cause predictable changes in QRS axis that may mimic pathological axis deviation 3. Always check for proper lead placement.
Bundle Branch Blocks: These can affect axis determination. Complete LBBB may change the mean QRS axis in various directions 2.
Age Considerations: Remember that children normally have a more rightward axis than adults, with gradual leftward shift throughout childhood 2.
Congenital Heart Disease: Leftward QRS-axis shifts are present in congenital defects with underdevelopment of the right ventricle or abnormal conduction system location 2.
Clinical Correlation: Left axis deviation should alert clinicians to the possibility of underlying structural heart disease 4. The presence of LAD can be a marker for various cardiac conditions, including structural heart disease and conduction system disease 1.
Scalar vs. Vector Methods: While vectorcardiography is theoretically more accurate for axis determination, the hexaxial reference system of the standard 12-lead ECG shows good correlation and is acceptable for routine clinical use 5.
By following this systematic approach, you can accurately assess for axis deviation on EKG and identify potential underlying cardiac pathology.