Right Axis Deviation

In right axis deviation the overall direction of electrical activity is distorted to
the right (between +90º and +180º)

Normal Limb Leads

Right Axis deviation Limb Leads

QRS is positive (dominant R wave) in leads III and aVF

QRS is negative (dominant S wave) in leads I and aVL

Right Axis Deviation ECG Example

Right axis deviation Causes

- Left posterior fascicular block
- Lateral myocardial infarction
- Right ventricular hypertrophy
- Acute lung disease (e.g. PE)
- Chronic lung disease (e.g. COPD)
- Ventricular ectopy
- Hyperkalaemia
- Sodium-channel blocker toxicity
- WPW syndrome
- Normal in children or thin adults with a horizontally positioned heart

Left Posterior Fasicular Block

In LPFB (aka left posterior hemiblock), impulses are conducted to the left
ventricle via the left anterior fascicle (LAF), which inserts into the upper lateral
wall of the left ventricle along its endocardial surface. This is instead of the (faulty) left posterior fascicle (LPF)

Diagnostic Criteria for LPFB

- RAD
- Small R waves with deep S waves in leads I and aVL
- Small Q waves with tall R waves in inferior leads (II, III, and aVF)
- QRS duration normal or slightly prolonged (80-110ms)
- Prolonged R wave peak time in aVF
- Increased QRS voltage in the limb leads
- No evidence of right ventricular hypertrophy
- No evidence of any other cause for right axis deviation

LAFB VS LPFB

LPFB is much less common than LAFB, as the broad bundle of fibres that comprise the left posterior fascicle are relatively resistant to damage when compared with the slim single tract that makes up the left anterior fascicle.

It is extremely rare to see LPFB in isolation. It usually occurs along with RBBB
in the context of a bifascicular block

Do not be tempted to diagnose LPFB until you have ruled out more significant causes of right axis deviation: i.e. acute PE, tricyclic overdose, lateral MI, right ventricular hypertrophy