Apparent bradycardia-dependent right bundle branch block associated with atrial fibrillation: Concealed electrotonic conduction as a possible mechanism

A 79-year-old woman with atrial fibrillation was reported in whom apparent bradycardia-dependent right bundle branch block was suggested. When a condu cted supraventricular impulse occurred within a critical period after the p receding conducted impulse, the impulse was blocked in the right bundle bra nch except when it fell in the supernormal period of the right bundle branc h. When the conducted impulse occurred between the critical period and anot her longer period, it was conducted without bundle branch block. When the i mpulse occurred beyond that longer period, it was usually blocked in the bu ndle branch again. However, when the impulse occurred beyond a still longer period, it was conducted without bundle branch block again. These findings suggest that when impulses fell in the right bundle branch shortly after t he preceding conducted impulses, they were blocked in both bundle branches; however, it seemed that concealed electrotonic conduction of the blocked i mpulses affected conduction of the subsequent impulses.