55  Fascicular Blocks

55.1 Left anterior fascicular block (LAFB)

  • EKG criteria:
    • LAD
    • ‘qR complexes’ (small Q + tall R) in I, aVL
    • ‘rS complexes’ (small R + deep S) in II, III, aVF
    • QRS nml/wide (80-110 ms), but not exceeding 120 ms

LAFB

55.2 Left posterior fascicular block (LPFB)

  • EKG criteria:
    • RAD
    • ‘qR complexes’ (small Q + tall R) in II, III, aVF
    • ‘rS complexes’ (small R + deep S) in I, aVL
    • QRS nml/wide (80-110 ms), but not exceeding 120 ms

55.2.1 Bifascicular block

  • RBBB + fascicular block (LAFB (more common) or LPFB)

55.2.2 Trifascicular block

  • most common: RBBB + fascicular block (LAFB or LPFB) + prolonged PR interval (1st degree AV block)
  • others:
    • bifascicular block + 2nd degree AV block
    • bifascicular block + 3rd degree AV block