The Role of the Potential FCB Region in ATs
This is the first study to describe this phenomenon in multiple ATs, mainly because various AT alternates provide the opportunity to show the different conduction features of the potential FCB region under different circumstances. Other scar-related ATs may also exist in the potential FCB region, but only one reentrant circuit cannot show them visually. Jaıs et al.8 previously noted the spontaneous zones of blocks in mapping at a series of scar-related ATs. Because no second AT occurred, no description of the changes in these zones of the block under different circumstances is possible. Some rare case reports have shown that a functional block line can sustain a reentrant pathway in a single AT episode and does not exhibit conduction block during coronary sinus pacing. We conclude first that the FCB region functions as an important obstacle that could be circled (such as mitral tricuspids in traditional perimitral reentrant circuits), which is usually the localized reentrant circuit. Second, since this region usually presented in MAT, it may play a role in reorganizing the conduction pathway and increasing the region conduction time that maintains the reentrant circuit. In multiple ATs, the FCB region guided the conduction orientation forming the reentrant circuit in one AT, while after ablation, its reconduction guided another AT circuit. Different from the isthmus, these regions are often not the target ablation site in any of the ATs which is observed or not.