Effects of Right Bundle Branch Block on the Antidromic Circus Movement Tachycardia in Patients with Presumed Atriofascicular Pathways

Antidromic Tachycardia in Patients with an Atriofascicular Fiber. Background: The typical and most common tachycardia in patients with atriofascicular pathways is a macro reentrant tachycardia, with anterograde conduction over the decrementally conducting bypass tract and retrograde conduction over the right bundle branch-His-AV node axis resulting in a short V-right bundle branch and short V-H interval. Objectives: To report on changes in rate and QRS configuration when right bundle branch block (RBBB) develops spontaneously during antidromic tachycardia using an atriofascicular fiber. Methods: Three of 25 patients with an antidromic circus movement tachycardia using a right-sided atriofascicular pathway showed episodes of right bundle branch block (RBBB) during ventriculo-atrial conduction. Effect of retrograde RBBB on tachycardia rate and QRS configuration was studied using intracardiac and extracardiac recordings. Results: All 3 patients showed prolongation of their V-A interval when retrograde RBBB occurred during tachycardia, resulting in a longer tachycardia cycle length. The VA time increase ranged from 85 to 100 msec, with a mean 346 ± 5 msec. Two of the 3 patients also showed a change in QRS configuration due to a more leftward shift of the frontal plane QRS axis. Conclusion: Rate changes in antidromic tachycardia in patients with atriofascicular fibers can be based on a shift in VA conduction from one bundle branch to the other. This may be accompanied by changes in the frontal plane QRS axis because of a change in ventricular activation sequence.