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Conduction Disorders

Left Bundle Branch Block

February 15th, 2021


Left bundle branch block occurs due to failure of conduction down the left bundle branch, resulting in depolarisation of the left ventricle after the right ventricle.
  • Look For

  • Wide QRS >120ms
  • Broad R wave in lateral leads (I, aVL, V5, V6)
  • Absent Q waves in I, V5 and V6
May be associated with left axis deviation, ST / T wave changes in the opposite direction to the QRS complex, or poor R wave progression.
  • Causes of Left Bundle Branch Block

  • Ischaemic heart disease
  • Hypertension
  • Dilated cardiomyopathy
  • Rheumatic heart disease
  • Aortic stenosis
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