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Left Bundle Branch Block



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.


  • ECG Findings

  • Wide QRS >120ms
  • Broad R wave in lateral leads (I, aVL, V5, V6)
  • Absent Q waves in I, V5 and V6
  • Diagnosis
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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