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ECG changes in left bundle branch block (LBBB)

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

ECG findings:

  • there is a Q in V1 and an R wave in V6 - there is depolarization of the right ventricle before the left. Thus despite the smaller muscle mass of the right ventricle, there is also an R in V1 and an S in V6. These changes may only appear as notches on the ECG.
  • subsequent depolarisation causes an S in V1 and another R in V6.

Left bundle branch block is best seen in V6 where there is an M pattern. An M pattern may also be seen in I and AVL.

Click here for an ECG example of LBBB

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