left posterior fascicular block 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. left posterior fascicular blockother namesleft posterior hemiblockspecialtycardiology 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.