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Test Findings
Test Findings

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.
    • 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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