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.