What is left axis deviation?

Left Axis Deviation (LAD)

Left axis deviation (LAD) is defined as a mean frontal plane QRS axis of -30° or more leftward in adults, representing an abnormal electrical activation pattern of the ventricles that may indicate underlying cardiac pathology. 1

Definition and Diagnostic Criteria

• LAD is characterized by a mean frontal plane QRS axis of -30° or more leftward in adults 1
• Normal QRS axis ranges vary by age:
  • Adults: +30° to +90°
  • Children 8-16 years: up to +120°
  • Children 5-8 years: up to +140°
  • Children 1-5 years: +10° to +110°
  • Neonates: +30° to +190° 1

Clinical Significance

LAD is not a disease itself but rather a marker that may indicate underlying cardiac conditions:

• Associated with structural heart disease:

  • Left ventricular hypertrophy
  • Coronary artery disease
  • Cardiomegaly
  • Congestive heart failure 1, 2

• Associated with conduction system disease:

  • Left anterior fascicular block (LAFB) - the most common cause of LAD 3
  • Left bundle branch block (LBBB) with LAD indicates more advanced disease 2, 4

Diagnostic Approach

When LAD is identified on ECG, the following approach is recommended:

1. Confirm true LAD and determine its severity
2. Evaluate for associated ECG findings:
   • LVH voltage criteria
   • ST-T wave abnormalities
   • Bundle branch blocks or fascicular blocks 1
3. Consider additional diagnostic testing:
   • Echocardiography to evaluate ventricular size/function, congenital defects, and pulmonary hypertension 1

Important Clinical Correlations

• Patients with LBBB and LAD have:

  • More myocardial scar tissue
  • More severe LV hypertrophy
  • Poorer response to cardiac resynchronization therapy 4

• Patients with chronic LBBB and LAD (compared to those with normal axis) show:

  • Greater incidence of myocardial dysfunction
  • More advanced conduction disease
  • Higher cardiovascular mortality
  • Longer P-R, A-H, and H-V intervals 2

Diagnostic Pitfalls

• LAD alone is not synonymous with LAFB

  • While LAD is often associated with LAFB, additional criteria should be considered, such as delayed inscription of the intrinsicoid deflection in lead aVL 5

• ECG has limited sensitivity (73%) for detecting pulmonary hypertension

  • A normal ECG does not rule out significant disease 1

• In children without known heart disease

  • Isolated LAD may not require further investigation if there are no symptoms or abnormal exam findings
  • Follow-up ECGs are recommended to monitor for changes or progression 1

Management Approach

Management should focus on identifying and treating the underlying cause rather than treating LAD itself:

• For LAD associated with structural heart disease:

  • Treat underlying conditions such as hypertension or aortic stenosis 1

• For LAD with conduction system disease:

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

• For LAD associated with ventricular tachycardia:

  • First-line treatment includes beta-blockers, verapamil, or sodium channel blockers 1

Regular clinical assessment and serial echocardiography are necessary to monitor progression in patients with underlying structural heart disease 1.