What does leftward axis deviation on an electrocardiogram (ECG) mean?

Left Axis Deviation on ECG: Diagnosis and Clinical Significance

Left axis deviation (LAD) on an electrocardiogram refers to a QRS axis between -1° and -90° and may indicate underlying structural heart disease or conduction system abnormalities. 1

Definition and Diagnosis

Left axis deviation is determined by analyzing the QRS complex orientation in the frontal plane leads, particularly leads I and aVF:

• When lead I is positive and lead aVF is negative, this indicates left axis deviation (-1° to -90°) 1
• Normal QRS axis in adults ranges from +30° to +90° 1
• Age-specific normal ranges should be considered, as children have different normal axis values 1

Common Causes of Left Axis Deviation

Conduction System Abnormalities

• Left anterior fascicular block (LAFB) - most common cause 2
  • Diagnostic criteria include:
    • QRS axis between -30° and -90°
    • Delayed intrinsicoid deflection in lead aVL 3
    • QRS duration typically <120 ms

Structural Heart Disease

• Left ventricular hypertrophy (LVH) 4, 1
  • Often accompanied by secondary ST-T abnormalities
  • May show increased QRS duration
  • P-wave abnormalities suggesting left atrial enlargement
• Inferior myocardial infarction
• Congenital heart defects (particularly ventricular septal defects)
• Cardiomyopathies

Clinical Significance and Risk Stratification

LAD discovered in isolation in asymptomatic patients may not require further investigation, but certain findings warrant additional workup 5:

1. ECG findings that suggest need for further evaluation:

   • More negative QRS axis (≤-42°) 5
   • Evidence of chamber enlargement or hypertrophy on ECG 5
   • Prolonged PR interval 6

2. Clinical findings that suggest need for further evaluation:

   • Abnormal cardiac physical examination 5
   • Symptoms of heart failure or angina 6
   • Advanced age 6

Prognostic Implications

LAD can have important prognostic implications in certain contexts:

• In patients with left bundle branch block, those with LAD have:
  • More advanced conduction disease
  • Greater incidence of myocardial dysfunction
  • Higher cardiovascular mortality 6
  • Greater risk of developing AV block 6

Management Approach

When LAD is detected on ECG:

1. Evaluate for signs and symptoms of heart disease:

   • Assess for exertional angina, heart failure symptoms
   • Perform careful cardiac examination

2. Consider echocardiography when:

   • QRS axis is significantly negative (≤-42°)
   • ECG shows chamber enlargement or hypertrophy
   • Abnormal cardiac physical examination findings
   • Symptoms of cardiovascular disease are present

3. Monitor patients with LAD and known conduction system disease:

   • Watch for progression to higher-degree AV block
   • Consider pacemaker implantation if symptomatic bradycardia or advanced AV block develops 1

Pitfalls and Caveats

• LAD alone should not be considered synonymous with left anterior fascicular block 3
• The presence of LAD should prompt consideration of underlying heart disease, but isolated LAD in asymptomatic individuals may not require extensive workup 5
• In children, normal axis values differ from adults, so age-specific norms should be applied 1
• Obesity can affect ECG voltage criteria and should be considered when interpreting findings 1

Remember that while LAD is a common ECG finding, its significance varies based on associated findings, patient age, and clinical context.