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2288 pages added, reviewed or updated during the last month (last updated: 19/4/2021)


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bundle branch block

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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.

Last reviewed 01/2018

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