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Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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This occurs if there is a failure of conduction of either the anterior or posterior fascicle of the left bundle. If there are no other conduction abnormalities then the duration of the QRS complex is not prolonged beyond 0.11s.

  • if there is left anterior fascicle block then this results in left axis deviation.
  • if there is left posterior fascicle block then this is associated with right axis deviation.

Click here for an example ECG of left anterior fascicular block

Click here for an example ECG of left posterior fascicular block

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