Left posterior fascicular block

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His-Purkinje system and hemiblocks


Diagnostic criteria include[1]:

  1. Right axis deviation (>110)
  2. QRS < 120ms
  3. qR in III and aVF
  4. rS in I and aVL


Axis Left axis deviation Right axis deviation
I and aVL Upright QRS Downgoing QRS
III Downgoing QRS Upright QRS


  • Usually associated with disease
  • Isolated LPFB associated with MI[3]
  • Exclude other causes of RAD (PE, COPD, RVH, Lateral MI)

See Also


  1. Surawicz B, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances. Journal of the American College of Cardiology. 2009; 53(11): 976–981.
  2. Mattu A and Brady WJ. ECG's for the Emergency Physician. BMJ Books. Sep 19, 2003.
  3. Godat FJ and Gertsch M. Isolated left posterior fascicular block: a reliable marker for inferior myocardial infarction and associated severe coronary artery disease. Clin Cardiol. 1993; 16(3):220-226.