Bundle branch reentrant ventricular tachycardia with two distinct components of QRS complex due to simultaneous dual transseptal conduction.

We report the case of a patient with bundle branch reentrant ventricular tachycardia having two distinct components of the QRS complex due to simultaneous dual transseptal conduction. The macroreentrant circuit consisted of anterograde conduction down the left bundle branch and retrograde conduction up the right bundle branch. Extensively injured myocardium in the interventricular septum isolated the two separate transseptal passages, which exhibited a "fast" and "slow" conduction property, respectively. The QRS configuration resulted from a wavefront propagating from the left bundle branch via "fast" transseptal conduction, followed by another more delayed wavefront propagating via "slow" transseptal conduction, which played an important role in determining this unique QRS morphology.