Left posterior fascicular block


A left posterior fascicular block, also known as left posterior hemiblock, is a condition where the left posterior fascicle, which travels to the inferior and posterior portion of the left ventricle, does not Electrical [conduction system of the heart|conduct the electrical impulses] from the atrioventricular node. The wave-front instead moves more quickly through the left anterior fascicle and right bundle branch, leading to a right axis deviation seen on the ECG.

Definition

The American Heart Association has defined a LPFB as:
  • Frontal plane axis between 90° and 180° in adults
  • rS pattern in leads I and aVL
  • qR pattern in leads III and aVF
  • QRS duration less than 120 ms
The broad nature of the posterior bundle as well as its dual blood supply makes isolated LPFB rare.