Left anterior fascicular block

His-Purkinje system and hemiblocks

Criteria

Diagnostic criteria include[1]:

  • Left axis deviation (-45 or more)
  • QRS 80-110ms
  • rS in II, III, and aVF
  • qR in I and aVL
  • Increased QRS voltage in the limb leads

LAFB vs LPFB[2]
LAFB LPFB
AxisLeft axis deviationRight axis deviation
I and aVLUpright QRSDowngoing QRS
IIIDowngoing QRSUpright QRS

Significance
  • Considered benign finding
  • LAFB may increase risk of afib, CHF, and death[3]

See Also

References
  1. Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice (6th edition), Saunders 2008.
  2. Mattu A and Brady WJ. ECG's for the Emergency Physician. BMJ Books. Sep 19, 2003.
  3. Mandyam MC, et al. Long-term outcomes of left anterior fascicular block in the absence of overt cardiovascular disease. JAMA. 2013; 309(15):1587-1588.
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