What is the significance and management of left axis deviation on an electrocardiogram (ECG)?

Left Axis Deviation on ECG: Significance and Management

Left axis deviation (LAD) on ECG should not be treated as a primary diagnosis but rather as a finding that requires clinical correlation with other ECG abnormalities and physical examination findings to determine its significance. 1

Definition and Normal Values

• In adults, normal QRS axis is between +30° and +90°, with left axis deviation defined as an axis <-30° 1
• Moderate left axis deviation is between -30° and -45°, while marked left axis deviation ranges from -45° to -90° 2
• Left axis deviation naturally occurs with aging as there is a tendency toward more leftward axis with increasing age 2, 1

Clinical Significance

• LAD may be associated with left ventricular hypertrophy (LVH) but should only be used as a supporting criterion rather than making the diagnosis on its own 2
• Marked left axis deviation (-45° to -90°) is often associated with left anterior fascicular block 2
• LAD can be a sign of underlying structural heart disease and should alert clinicians to this possibility 3
• In isolation, LAD has limited prognostic value and must be interpreted in context with other clinical and ECG findings 1

Diagnostic Approach

• When LAD is found with other ECG abnormalities, particularly:

  • ST-T wave abnormalities (which may indicate LVH with strain) 2
  • QRS prolongation 2
  • Chamber enlargement patterns 1
  • These combinations warrant more thorough cardiovascular evaluation

• In pediatric patients, factors that should prompt further evaluation include:

  • QRS axis ≤-42° 4
  • ECG evidence of chamber enlargement or hypertrophy 4
  • Abnormal cardiac physical examination findings 4

Management Algorithm

1. For isolated LAD with normal physical examination and no other ECG abnormalities:

   • No specific treatment or further evaluation is required 1
   • Consider age-related changes as a potential cause 2

2. For LAD with abnormal physical examination findings:

   • Further cardiac evaluation with echocardiography is warranted 5
   • The sensitivity of physical examination by a cardiologist for detecting abnormalities in patients with LAD is approximately 97% 5

3. For LAD with other ECG abnormalities:

   • Obtain echocardiography to evaluate for structural heart disease 1, 4
   • Consider additional testing based on clinical suspicion (stress testing, cardiac MRI) 1
   • Treat any underlying conditions identified (hypertension, valvular disease) 1

Special Considerations

• In the presence of left anterior fascicular block, R-wave amplitude in leads I and aVL are not reliable criteria for LVH 2
• The presence of ST-T wave abnormalities with LVH is associated with larger left ventricular mass and higher risks of cardiovascular complications 2
• In pediatric patients, the cost-effectiveness of performing echocardiography in all patients with LAD is questionable when physical examination is normal 5

Common Pitfalls

• Overdiagnosis - treating LAD as a primary diagnosis rather than a finding requiring clinical correlation 1, 3
• Relying solely on LAD for diagnosis of left anterior fascicular block - additional criteria such as qR pattern in lead aVL and R-peak time in lead aVL of 45 ms or more should be considered 2, 6
• Failing to recognize that LAD alone is insufficient for diagnosis of structural heart disease 7