Slow heart rate. Lbbb is abnormal when slow heart beats cause syncope and symptomatic bradycardia - rbbb alone doesnot need treatment unles sit causes additional bloks any way need evaluation prior for pm treatment with ep study.
Heart block. Often, pacemakers are inserted because of conduction abnormalities between the upper and lower chambers of the heart. If a patient has a left bundle branch block and is undergoing pacemaker implantation, the ventricular lead could inadvertantly bump against the right bundle branch and cause complete heart block. This could cause slowing of the heartbeat prior to permanent placement of the lead.