The clinician is frequently confronted with a difficult therapeutic decision when patients with chronic bundlebranch block have syncope or other transient neurologic symptoms. The decision of whether and when to implant a permanent pacemaker in such patients is based on a number of clinical and electrophysiologic variables. We provide herein an anatomic and ECG basis for the diagnosis of these conduction disturbances, discuss their natural history with special reference to cardiac electrophysiologic subsets, and offer a rational approach to management.
After emerging from the atrioventricular (AV) node, the cablelike bundle of His penetrates the membranous interventricular septum and courses inferiorly for approximately 15 mm, then bifurcates to form the right and left bundle branches.1 The right bundle branch traverses the right side of the interventricular septum. Its proximal branches terminate at the right ventricular apex. Its peripheral ramifications spread over the right side of the muscular interventricular