Right Bundle Branch Block (RBBB)

Introduction

due to its endocardial course, the right bundle branch in the heart is relatively fragile and is easily impaired resulting in either an incomplete or a complete RBBB on the ECG
in RBBB, the RV is depolarised AFTER the LV and hence results in the ECG effects on the latter part of the QRS as well as ST-T changes due to delayed repolarisation

studies suggest that of the general population of adults without cardiovascular disease, incomplete RBBB is present in almost 5% of men and 2-3% of women, while complete RBBB was present in 1.4% of men and 0.5% of women ¹⁾
presence of RBBB increases with age such that by age 80yrs some 11% have RBBB

normal variant
stretching of the RBB due to RV strain from increased RV pressure
- if acute this may be due to:
  - fluid overload
  - pulmonary embolism (PE)
minor chest trauma
cardiac catheterisation
cardiac surgery - either temporary or permanent RBBB
IHD
HT
RhHD
CHD esp. ASD, VSD, Fallot's tetralogy
pericarditis, myocarditis
cor pulmonale
cardiomyopathy
sarcoidosis
scleroderma
Brugada syndrome - if associated ST elevation V1-2 - potentially fatal in young people
Chaga's disease
endomyocardial fibrosis
Lenegre disease or Lev disease (progressive cardiac conduction system diseases) esp. in the elderly
other conditions

QRS > 0.12sec, plus,
- M-shaped pattern in V1
  - large R' wave (the second R wave is larger than the first R wave) in V1/2
  - sometimes V1 may just have a broad, notched R wave and if this is the case, the duration of teh R wave peak time should be > 0.05secs
- broad and deep, slurred S in leads V5/6
  - duration of S wave is greater than that of the R wave in leads V5/6, or greater than 40ms in I and V6
NB. does not alter the electrical axis of the heart so if there is LAD then there is also LAFB, while if there is RAD, then there is also RAFB
unlike LBBB, usually does not interfere with ECG Dx of AMI
- acute cor pulmonale may cause RBBB plus large Q waves in V1-3 and the inferior leads

incomplete RBBB in those without known cardiovascular disease does NOT appear to increase mortality ²⁾
complete RBBB may be a pointer to underlying clinical conditions as in the aetiology list, especially if it is acute
RBBB can be a marker for underlying subclinical cardiac conditions, including diastolic dysfunction with preserved systolic function ³⁾
there are conflicting studies as to whether complete RBBB in those without known cardiovascular disease is associated with increased mortality and impaired exercise tolerance but it appears this may be more important in men than women ⁴⁾
the presence of RBBB in those with cardiovascular disease does appear to associated with increased mortality although not all studies support this ⁵⁾
RBBB appears to be a risk factor for long term mortality in those with congestive cardiac failure ⁶⁾
RBBB has been reported to be associated with an increased risk for progression to high‐degree atrioventricular block ⁷⁾

¹⁾ , ²⁾ , ³⁾ , ⁴⁾ , ⁵⁾ , ⁷⁾

⁶⁾