Conclusions
The potential FCB region is common in ATs with over two types of
reentrant circuits, especially in scar-related localized reentry. The
occurrence of this substrate may be due to the native scars or
progressed scars of myocardium disease. This substrate species could
exhibit DPs or fractionated and complex potentials and showed conduction
block through this area in one AT but not in another AT or in sinus
rhythm. The FCB region maintains reentrant circuits as an obstacle, and
the changefulness of this substrate may be one of the important reasons
for the high recurrence of related ATs.