bundle branch block
Last reviewed 01/2018
In this condition there is abnormal conduction through the right or left bundle branches and a consequent delay in the depolarisation of part of the ventricular muscle. When the heart is in sinus rhythm, ventricular conduction along a slower, abnormal pathway results in a QRS complex of greater than 0.12 sec but with a constant PR interval.
A block of both bundles is equivalent to third degree, or complete, heart block.
Thus three types of bundle branch block may occur:
- bundle branch block involving both branches
- a right bundle branch block
- a left bundle branch block
Right bundle branch block:
- principle indicator is "M" in V1 and V2.
- also, S wave: prominent in V6, slurred in I.
Left bundle branch block:
- principle indicator is "M" in V5 and V6.
- also, tall and very broad in I and aVL.