How can you diagnose axis deviation on an electrocardiogram (EKG)?

How to Diagnose Axis Deviation on an EKG

The most practical method to determine axis deviation is using leads I and aVF, which are orthogonal in the hexaxial system and provide the most accurate axis calculation for clinical interpretation. 1

Quick Visual Method Using Leads I and aVF

The simplest approach uses the quadrant method with these two perpendicular leads 1:

• Normal axis (+30° to +90°): Both lead I and aVF are predominantly positive 2
• Left axis deviation (<+30°): Lead I is positive, but aVF becomes isoelectric or negative 2
• Right axis deviation (>+90°): Lead aVF is positive, but lead I becomes isoelectric or negative 3
• Extreme axis deviation (-90° to -180°): Both lead I and aVF are predominantly negative 3

Defining Normal vs. Abnormal Axis

Adults

• Normal range: +30° to +90° 2
• Left axis deviation: Less than +30° 2
  • Moderate: -30° to -45° 2
  • Marked: -45° to -90° (often indicates left anterior fascicular block) 2
• Right axis deviation: Greater than +90° 3
• Extreme axis: +90° to -180° (or equivalently stated as between 60° and 190°) 3

Pediatric Populations

Age-specific norms differ dramatically from adults 3:

• Newborns: Normal axis ranges from 55° to 200°, with what would be "right axis deviation" in adults being completely normal 4
• Ages 1-5 years: Normal range is 10° to 110° 3
• Ages 5-8 years: Normal range extends to 140° 3
• Ages 8-16 years: Normal range extends to 120° 3

Precise Calculation Method

For borderline cases or when precision matters 1:

1. Identify the most isoelectric (equiphasic) limb lead - where positive and negative deflections are equal 1
2. The axis is perpendicular (90°) to this lead 1
3. Determine direction by finding which perpendicular lead has the most positive deflection 1
4. Alternative: Calculate using the formula based on leads I and aVF amplitudes, as this combination shows the best correlation with vectorcardiography (r = 0.85-1.00) 1, 5

Clinical Context and Associated Findings

Left Axis Deviation

When you identify left axis deviation, assess for 2:

• Left anterior fascicular block criteria 3, 2:
  • Frontal plane axis between -45° and -90° 3
  • qR pattern in lead aVL 3
  • R-peak time in lead aVL ≥45 ms 3
  • QRS duration <120 ms 3
• Left ventricular hypertrophy 2
• Age-related changes (can be normal variant with aging) 2

Right Axis Deviation

Consider 3:

• Complete or incomplete RBBB (look for rsr' pattern in V1/V2, wide S waves in I and V6) 3
• Right ventricular hypertrophy 3
• Congenital heart disease in pediatric patients 3

Critical Pitfalls to Avoid

• Don't apply adult criteria to children - a QRS axis of 120° is pathologic in adults but normal in young children 3, 4
• Don't overdiagnose left axis deviation as a primary diagnosis - it's a finding that requires clinical correlation, not a standalone diagnosis 2
• Watch for limb lead reversals - these can create artifactual axis deviations with predictable patterns (e.g., mirror-image reversal shifts axis to 180° - n) 6
• Don't ignore computer errors - gross axis miscalculations by automated systems occur and should be verified visually using leads I and aVF 1
• Consider technical factors - lead placement errors, especially in neonates, can mimic axis deviation 4

When Axis Deviation Matters Clinically

• Isolated left axis deviation without other ECG abnormalities has limited diagnostic value and should not drive management decisions 2
• Marked left axis deviation (-45° to -90°) warrants evaluation for left anterior fascicular block and underlying structural disease 2
• Extreme axis deviation in any age group suggests significant pathology and requires further investigation 3
• New axis deviation compared to prior ECGs is more concerning than chronic stable findings 7