Insight into the Role of the Potential FCB Region in Other
Atrial-related Arrhythmias
In addition to the types of ATs we mentioned, the mechanism of another
kind of AT with CL alternans is also related to the FCB, which is a rare
phenomenon.13-15 In one type, CL alternans resulted
from an intermittent 2:1 conduction block within the channel of the
small circuit. The other type, the alternate block and conduction of the
2 channels with different velocities, results in CL
alternans.13 The FCB channel of these ATs usually
occurs with severe atrial scarring of different causes (prior cardiac
surgery, catheter ablation of AF or fibrotic atrial cardiomyopathy).
Similar to our study, the FCB region often occurs near the scar area.
This may be another expression form of the FCB region.
The DP region means a smaller block area than some of the silent areas
because the still potential could be recorded bilaterally. Most DPs or
fragmented potentials are more common in AT or AF than in sinus rhythm
because the bilateral scar tissue that is recognized in ATs is excited
at the same time in sinus rhythm due to the normal conduction pattern,
not with a certain direction as atrial flutter (AFL). As we observed in
this study, the FCB region participated and maintained the reentrant
circuit at different CLs or pathways (Figs. 1 and 2). This phenomenon
suggests that some AF patients who still experience recurrence of AF
after PVI ablation may also have neglected FCBs, while they have normal
conduction substrates after mapping under sinus rhythm. The FCB may
maintain the AF under some conditions. More electric anisotropy is
related to a more uncertain conduction mode, which may lead to AF.
Recently, it has been shown that the ablation of Marshall veins or
Bachmann’s bundle may further advance the success rate of
AF,12,16 not only for the trigger in these regions but
also for reducing the connection with the atrium that decreases the
electric anisotropy of conduction. Judging the electric anisotropy
region, such as the FCB, may provide new insight into the formulation of
the AF ablation strategy.
ATs with over two types of reentrant circuits are often associated with
more complex ablation procedures.1 The ablation
strategy in our study still depended on the activation mapping results.
Despite careful mapping, the reentrant circuit of the second AT could be
forecasted before the first ablation in only 1 patient with a
double-loop localized reentry who did not show the FCB region (Fig. 4).
The instability of the functional zone made the second or third AT
unpredictable (Figs. 1 and 2). The occurrence of FCB may depend on the
circle length of the ATs, and entrainment mapping may transform
tachycardia, confusing the mechanism of ATs. Substrate mapping is also
limited by different potentials under different conditions and does not
seem to make much sense in optimal ablation strategies. Even though an
effective method for identifying a potential FCB region is not yet
available, the ablation strategy for addressing this specific substrate
is controversial. A future computer simulation may well be used to
identify the necessary conditions for FCB and an intervention strategy.