Main Findings
Convertibility of the FCB regions occurred in 5 of 8 patients in our
study, suggesting that it may not be an uncommon
electrophysiological feature in ATs, especially scar-related ATs. This
substrate species could be described as exhibiting DPs or fractionated
and complex potentials and showed a conduction block through this area
in one AT but not in another AT or in sinus rhythm. In 8 of 14 ATs, the
FCB regions were the main obstacle and the center of the reentrant
circuit (such as in Fig. 1 AT1, Fig. 2 AT2). Other FCB regions may
participate in reorganizing the conduction pathway maintaining ATs (such
as in Fig. 2 AT3, Fig. 3 AT2). A specific FCB region acts as an obstacle
only for its corresponding AT and does not seem to play a substantial
role in other ATs. In severe native scars or progressed scars related to
myocardium disease, the electrophysiology coupled with the complex
substrate has not been summarized systematically. The FCB region is
occasionally described in atrial-related arrhythmia, and although it is
thought to play an important role in some types of arrhythmia, there has
been no method of analyzing this mechanism and definitively determining
its role.4 Our study is the first to describe the
convertibility of FCB regions and their important role in maintaining
some stable ATs. The instability of the FCB region may be the reason for
the high recurrence of related ATs, but this possibility has been shown
in only one specific AT and is not easy to identify with conventional
mapping procedures. The potential FCB region described in our study may
account for another mechanism of multiple ATs.