If you get your left bundle branch taken out, your left ventricle depolarises AFTER the right ventricle has finished depolarising. This results in a significantly prolonged QRS.

Features of LBBB:

left bundle branch block


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

References

From "the ECG made easy", by Hampton (2003), and ECGs shamelessly stolen from Life in The Fastlane without any sort of permission, but in the non-commercial spirit of free education

2012 ACCF/AHA/HRS Focused Update of the 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities A Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines