Masquerading Bundle-Branch Block—Electrophysiological Correlation

The term masquerading bundle-branch block has been used to describe a peculiar electrocardiographic abnormality in which the standard leads exhibit a left bundle-branch block pattern while the precordial leads manifest a right bundle-branch configuration. Autopsy studies of patients who have had this electrocardiographic pattern in life have shown diffuse conduction system disease, but direct recordings of conduction system function have never been reported. We recently cared for a man with masquerading bundle-branch block, and in this report we summarize the results of invasive electrophysiological testing. Our findings confirm that masquerading bundle-branch block can be associated with severe and diffuse conduction system disease, and that patients with this finding may require permanent pacemaker implantation, especially if they are symptomatic.