What is the workup for left axis deviation?

Workup for Left Axis Deviation

Left axis deviation (LAD) on ECG requires a focused cardiac workup with echocardiography primarily indicated when there are abnormal cardiac physical examination findings, ECG evidence of chamber enlargement/hypertrophy, or a QRS axis ≤-42°.

Definition and Normal Values

Left axis deviation is defined as a mean frontal plane QRS axis <-30° in adults 1. Normal QRS axis values vary by age:

• Adults: 30° to 90° (LAD when <-30°)
• Children 8-16 years: 0° to 120° (LAD when <0°)
• Children 5-8 years: 0° to 140° (LAD when <0°)
• Children 1-5 years: 5° to 100° (LAD when <5°)
• Infants 1 month to 1 year: 10° to 120° (LAD when <10°)
• Neonates: 30° to 190° (LAD when <30°)

Clinical Significance

LAD is one of the most commonly encountered ECG abnormalities and may indicate underlying structural heart disease 2. It can be categorized as:

• Moderate LAD: -30° to -45°
• Marked LAD: -45° to -90°

Diagnostic Approach

Step 1: Assess for High-Risk Features on ECG

Look for associated ECG findings that increase the likelihood of structural heart disease:

• QRS axis ≤-42° (higher risk) 3
• Evidence of chamber enlargement or hypertrophy 3
• Pathological Q waves
• ST-segment depression or T-wave inversion
• Conduction abnormalities (especially left anterior fascicular block)

Step 2: Focused Cardiac Examination

Carefully evaluate for:

• Abnormal heart sounds (murmurs, gallops)
• Signs of heart failure
• Irregular rhythm
• Abnormal blood pressure

Step 3: Further Diagnostic Testing

Echocardiography is indicated when:

• Abnormal cardiac physical examination findings (75% of patients with LAD and heart disease have abnormal exam findings) 3
• ECG shows chamber enlargement or hypertrophy (38% of patients with LAD and heart disease have these findings) 3
• QRS axis ≤-42° (significantly associated with underlying heart disease) 3
• Symptoms of cardiovascular disease are present

Consider additional testing based on clinical suspicion:

• Cardiac MRI: If echocardiogram suggests cardiomyopathy or scar tissue
• Exercise testing: For symptoms discrepant with clinical findings
• Cardiac catheterization: To rule out coronary artery disease in patients at risk due to age or other factors 1

Common Causes of LAD

1. Left Anterior Fascicular Block (LAFB)

   • Most common cause of LAD
   • Diagnostic criteria 1:
     • Frontal plane axis between -45° and -90°
     • qR pattern in lead aVL
     • R-peak time in lead aVL ≥45 ms
     • QRS duration <120 ms

2. Structural Heart Disease

   • Cardiomyopathies (hypertrophic, dilated)
   • Congenital heart defects (especially ASD)
   • Valvular heart disease
   • Coronary artery disease

3. Conduction System Disease

   • Left bundle branch block with LAD has worse prognosis than LBBB with normal axis 4
   • Higher risk of developing AV block 4

4. Borderline Variant in Athletes

   • In asymptomatic athletes with negative family history, LAD may be considered a borderline variant not requiring additional investigation if present in isolation 1

Cost Considerations

The cost-effectiveness of echocardiography varies significantly based on physical examination findings:

• Normal PE: $8,365 per abnormality detected
• Abnormal PE: $263 per abnormality detected 5

Pitfalls to Avoid

1. Overinvestigation: LAD discovered in isolation in asymptomatic pediatric patients may not necessitate further cardiovascular investigation 3

2. Underinvestigation: Patients with LAD and LBBB have more myocardial scar tissue, more severe LV hypertrophy, and poorer outcomes with cardiac resynchronization therapy 6

3. Age-inappropriate interpretation: Remember that normal QRS axis values vary significantly by age, especially in children 1

4. Missing biventricular hypertrophy: In the presence of ECG criteria for LVH, the presence of right axis deviation, prominent S waves in V5/V6, and signs of right atrial abnormality may indicate biventricular hypertrophy 1