4.4 Other AF substrates and AF rotors
Recent clinical and experimental studies have demonstrated that
persistent AF might be maintained by AF rotors but the mechanisms
linking rotor formation and persistent perpetuation are still unknown.
Narayan et al. reported biatrial basket- and specific software-based
mapping to delineate the stable AF rotor sources.15Haissaguerre et al. developed specific algorithms to identify localized
sources and atrial propagation occurring simultaneously during ongoing
AF using body surface mapping.16 However, a poor
electrode contact would lead to an insufficient verification of the
imaging algorithms.17 The previous studies reported
that low voltage areas (LVAs) or CFAE areas could be associated with an
AF substrate, but the relationship between that substrate and AF rotors
is still in debate.18 CFAEs are also considered
ablation targets, but a multicenter trial showed that there was no
additional benefit of a CFAE-targeted ablation in patients with
persistent AF.19 In this study, no significant
correlation between the NPAs and CFAE areas could be found, which was
completely consistent with the previous report.10Several limitations could be found to accurately assess the unstable and
meandering rotors by the conventional mapping methods based on the
bipolar electrogram. First, the bipolar electrograms depended on the
orientation of the electrode catheters to the propagating wavefront and
cardiac rhythm. Of note, the distribution of the LVAs could change
according to the pacing site. Second, the true myocardial activation and
near far-field myocardial activation were mixed and those could not be
distinguished by the bipolar electrograms during AF.
To make it possible to achieve a rapid prediction of the atrial
excitation during AF, both a computer simulation (in silico) part and
specialized artificial intelligence part were incorporated into the
ExTRa Mapping system.10 Combined with the timing of
the action potential onset determined by the intra-atrial signals, the
in silico part calculated the virtual atrial action potentials based on
the in silico model of human persistent AF.20Recently, an experimental study has excellently demonstrated that the
phase map sequence of the ExTRa Mapping is consistent with that of
high-resolution optical mapping.21 Therefore, we
considered that the ExTRa Mapping provided us more specific ablation
targets associating with AF drivers.
Furthermore, LGE-MRI could provide us with the fixed tissue properties
regardless of the cardiac rhythm and pacing site. Considering both the
electrical and structural substrate obtained by ExTRa Mapping and
LGE-MRI, we might overcome those conventional mapping limitations.