Features of LBBB:

Broad QRS
o Dominant S wave in V1
o Broad R wave in lateral leads
o Absence of Q waves in lateral leads
o There is prolonged R wave peak time in lateral leads

Additional features:

o The ST segments and the QRS complexes always point in opposite directions
o There should be left axis deviation

o The right ventricle depolarizes first, and this eliminates the normal septal Q waves in the
lateral leads

INCOMPLETE Left Bundle Branch Block
- Normal QRS duration, but otherwise looks like a left bundle branch block

Causes of Left Bundle Branch Block

- Ischaemia
- Aortic stenosis or severe hypertension
- Dilated cardiomyopathy
- Primary degenerative disease of the conducting system (eg. Lenegre disease)
- Digoxin toxicity
 

Consequences of Left Bundle Branch Block

- Independent predictor of increased mortality in patients with coronary artery disease
- Dyssynchronous left ventricle: thus, decreased ejection fraction
 

Management options for Left Bundle Branch Block

- In absence of other conduction abnormalities, with normal ejection fraction: do nothing.
- If LVEF is poor (<35%) or there is some other heart block, go with BIVENTRICULAR PACING