Syncope in a patient with right bundle branch block and left posterior fascicular block
This patient presents a bifascicular block with association between complete right bundle branch block and left posterior fascicular block. This form is much less common than the right bundle branch block + left anterior fascicular block association and certainly much more worrisome. Indeed, the risk of evolution toward a complete atrioventricular block is increased, the left anterior hemibranch, the only one ensuring conduction, being the most vulnerable. This is therefore an indication for pacemaker implantation especially when the patient is symptomatic and when other plausible causes of syncope have been eliminated.
It is difficult to differentiate right block + left posterior fascicular block and right block + right ventricular hypertrophy, a right axis deviation being observed in both cases. The absence of clinical or ultrasound evidence indicative of right ventricular hypertrophy thus suggests in this instance the diagnosis of a bifascicular block.