Simultaneous Block Proximal and Distal to His Bundle

The term concealed conduction describes the effects of a cardiac impulse partially penetrating the atrioventricular (AV) junction and disturbing the conduction or formation of subsequent impulses.¹,²Examples of this phenomenon include the PR prolongation following either a blocked atrial or interpolated ventricular premature contraction, the compensatory pause following a premature ventricular beat in atrial fibrillation, and the resetting of a junctional pacemaker following retrograde penetration of a ventricular premature beat in a patient with AV dissociation. Catheter recording of His bundle electrographs has furthered understanding of concealed conduction by permitting the precise localization of sites of conduction delay following premature beats.³This technique also allowed the documentation of a rare form of concealed conduction, the occurrence of second-degree AV block due to the retrograde penetration of concealed junctional premature depolarizations.⁴,⁵These depolarizations, electrocardiographically silent because of antegrade and retrograde block, were easily recorded with an electrode catheter.