What are the normal and abnormal degrees for the electrical axis of the heart (Electrocardiogram, ECG)?

Normal and Abnormal Electrical Axis of the Heart

In adults, the normal QRS axis is between +30° and +90°, while abnormal axis deviations include left-axis deviation (<+30°), right-axis deviation (>+90°), and extreme axis deviation (>+180° or <-90°). 1

Adult Axis Classifications

According to the American Heart Association/American College of Cardiology Foundation/Heart Rhythm Society guidelines:

• Normal axis: +30° to +90°
• Left-axis deviation:
  • Moderate: -30° to 0°
  • Marked: -45° to -90° (often associated with left anterior fascicular block)
• Right-axis deviation:
  • Moderate: +90° to +120°
  • Marked: +120° to +180° (often associated with left posterior fascicular block)
• Indeterminate axis: When there is no dominant QRS deflection (equiphasic QRS complex)

Age-Related Variations

Neonates and Children

The electrical axis varies significantly with age:

• Neonates:

  • Normal range: +60° to +190° 1
  • "Extreme right axis" is considered +90° to +190° 1

• Children 1-5 years:

  • Normal range: +10° to +110° 1

• Children 5-8 years:

  • Normal range may extend to +140° 1

• Children 8-16 years:

  • Normal range may extend to +120° 1

Clinical Significance of Abnormal Axis

Abnormal axis deviation can indicate underlying cardiac pathology:

• Left-axis deviation in adults is often associated with:

  • Left anterior fascicular block
  • Left ventricular hypertrophy
  • Inferior myocardial infarction
  • Aortic valve disease (57.15% of patients with LBBB and aortic valve disease have LAD) 2

• Right-axis deviation in adults is often associated with:

  • Right ventricular hypertrophy
  • Left posterior fascicular block
  • Lateral myocardial infarction
  • Pulmonary hypertension

• Extreme axis deviation may indicate:

  • Ventricular pre-excitation syndromes
  • Complex congenital heart disease

Prognostic Implications

Abnormal axis deviation has been associated with increased mortality:

• Abnormal P-wave axis has been linked to increased mortality in both patients with and without Chagas disease 3
• Abnormal QRS and T-wave axes have been associated with increased mortality in patients with Chagas disease 3, 4
• T-wave axis deviation can increase the risk of sudden cardiac death nearly sixfold in certain populations 4

Special Considerations

1. Lead Placement: Incorrect lead placement can falsely suggest axis deviation
2. Body Habitus: Axis is influenced by body build and position
3. Congenital Heart Disease: Leftward QRS-axis shifts are present in congenital defects with underdevelopment of the right ventricle (e.g., tricuspid atresia) 1
4. Cardiac Resynchronization Therapy: QRS axis may influence response to therapy, with better outcomes when lead placement is matched to pre-existing axis deviation 5

Common Pitfalls

1. Age-appropriate interpretation: What appears as right-axis deviation in adults may be normal in children
2. Confusing axis deviation with bundle branch blocks: While they often coexist, they represent different electrical phenomena
3. Overlooking indeterminate axis: When QRS complexes are equiphasic, the axis cannot be determined conventionally
4. Failing to consider clinical context: Axis deviation should be interpreted in the context of other ECG findings and clinical presentation

Remember that axis determination is just one component of ECG interpretation and should be integrated with other findings for comprehensive cardiac assessment.