What is right bundle branch block?
Occurs when there’s a delay or blockage in electrical conduction through the right bundle branch of the His-Purkinje system
Mechanism of RBBB
- RV depolarises later than the left
- LV depolarises normally
- Impulse spreads form LV across septum to RV
- Slows right-sided activation
Cardiac causes of RBBB
- Ischaemic heart disease
- Cardiomyopathies
- Myocarditis
- Congenital heart disease
- RVH
- degenerative fibrosis of conduction system
Non-cardiac causes of RBBB
- Pressure or volume overload (right heart strain)
- Iatrogenic/trauma
- Normal variant
Treatment of isolated RBBB
- No specific treatment
- usually benign
- Monitor and treat CV risk factors
Treatment of RBBB secondary to cardiac or pulmonary disease
- Treat underlying cause
Treatment of symptomatic or advanced conduction disease RBBB
- If occurs with syncope or bradyarrhythmia due to more extensive conduction disorder
- PPM may be indicated
Main changes in ECG for RBBB
- Increase in QRS duration
- Secondary R wave in leads facing RV (V1 and V2)
- M-shaped complex
- Broad S wave in LV leads and lead I
What is left bundle branch block?
Delay or complete block or electrical conduction through the left bundle of the His-Purkinje system
Mechanism of LBBB
- RV depolarises first via normal route
- Impulse spreads across septum to activate LV late
- Septal depolarisation is reversed
- Right to left depolarisation
Causes of LBBB
- Ischaemis HD
- Structural/degenerative HD
- Post-cardiac intervention
- Congenital HD
- Infiltrative/inflammatory disorders
Treatment of isolated LBBB
- No specific treatment
- Investigate and treat underlying cause
Treatment of new or acute LBBB with chest pain
- Treat as acute coronary syndrome until proven otherwise
- Apply Sgarbossa criteria to diagnose MI in presence of LBBB
Treatment of LBBB with LV dysfunction of HF
Cardiac resynchronisation therapy (CRT)
Treatment of LBBB with syncope or advanced conduction disease
Consider PPM
Main ECG changes for LBBB
- Prolonged QRS curation
- Broad, notched R wave
- V1-V3 = deep S waves; looks like a ‘W’
- V5-V6, I, aVL = M shaped R waves
Left bundle branch divisions
- 2 main subdivisions
- Anterior and posterior fascicles
What is a fascicular block?
Block in either anterior or posterior fascicle (in left bundle branch)
Types of fascicular blocks
- Left anterior fascicular block
- Left posterior fascicular block
- Bifascicular block
- Trifascicular block
What is a bifascicular block?
When 2 of the 3 fascicles are blocked
What is trifascicular block?
- Block in all 3 fascicles
- Or block in 2 and delayed conduction in the 3rd
Mechanism of LAFB
- Block of the left anterior fascicle causes delay in activation of there anterosuperior portion of LV
- Impulse travels down posterior fascicle first
- Activates inferior and posterior LV then the anterolateral LV
- Leads to leftward and superior QRS axis
Common causes of LAFB
- Ischaemic HD
- HT/LVH
- Aortic valve disease
- Cardiomyopathy
- Degenerative fibrosis
- Aging conduction system
Treatment of LAFB
- No treatment if isolated
- Investigate underlying cause
- Monitor
- If symptomatic to with conduction defects consider PPM
