Left posterior fascicular block

A left posterior fascicular block (LPFB), also known as left posterior hemiblock (LPH), is a condition where the left posterior fascicle, which travels to the inferior and posterior portion of the left ventricle, does not 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.