Limitations
This study has several limitations: (1) The patients included in this retrospective study were a highly selected group referred for RF catheter ablation, and the number of patients was limited. (2) The absence of systematic pacing and entrainment because of the risk of inducing AF is a limitation in this study, and the FCB depends on the circuit length of the ATs. Entrainment mapping may transform tachycardias and confuse the understanding of the mechanisms of ATs. (3) We did not perform direct epicardial mapping in patients with a suspected epicardial connection, and therefore, our understanding of these potential connections and the relation with the FCB region remains speculative. (4) The voltage mapping in the Carto system was limited in the present FCB because this region often showed DPs or FPs, of which thresholds often fell to the normal or scar border zone and were not distinguishable from other tissues. (5) While the FCB region is important in maintaining reentry as an obstacle, there is still a lack of effective measures to recognize it without a particular AT episode. Although the FCB was related to scarring of the atrium but not the target ablation site under activation mapping, substrate ablation as a strategy aimed at the FCB region to avoid recurrence of other ATs still needs careful deliberation.