Novel strategies for atrial substrate assessment

Recent technological advances and a better understanding of the processes underpinning AF have spawned novel approaches to characterizing the atrial substrate and guiding ablation strategies. Being the rhythm of interest, mapping in AF would logically seem advantageous in potentially identifying sites involved in maintaining the arrhythmia, but has been challenging owing to the continually changing activation patterns and uncertainty regarding the significance of such activity. High-resolution mapping and novel signal processing algorithms has made this more feasible.
Hwang et al., performed voltage assessment during AF in a cohort of 50 patients with non-paroxysmal AF and identified LVAs as points with bipolar voltage <0.5mV (136). Patients randomized to the intervention arm underwent PVI plus adjunctive ablation of CFAEs located within LVZs. Compared to a standalone PVI strategy, PVI+CFAE ablation was associated with improved freedom from AF at 12 months, although the overall freedom from any atrial arrhythmia did not differ between the groups. Jadidi et al., similarly targeted CFAEs co-locating with LVAs during substrate assessment in AF (21). Selective ablation of CFAEs displaying prolonged activation and rapid firing was frequently associated with acute termination of AF to SR, as well as improved freedom from AF on follow-up. Further analysis of CFAEs at sites of AF termination demonstrated that all were located within or adjacent to LVAs, and had lower mean voltage than other parts of the atrium (137). Malaczynska-Rajpold et al. also employed high resolution mapping to identify consistent drivers for AF and report improved AF-free survival in patients with either persistent or long-standing persistent AF (138). Our group have also utilized non-contact charge density mapping for panoramic assessment of atrial activity in AF to identify potentials sites critical for AF maintenance (139). Targeted ablation of such drivers as an adjunct to PVI improved outcomes compared to a conventional linear ablation strategy.
Substrate assessment in AF may therefore provide mechanistic insights to guide intervention, which may be more relevant in the clinical setting. Indeed LVAs identified during mapping in AF more accurately matched late gadolinium enhancement observed on magnetic resonance imaging than LVAs identified in sinus rhythm (140). The study suggested maintaining stable catheter position for more than 4 seconds would suffice in extracting maximal voltage in AF, presumably being an adequate time to allow for the electrode pair to encounter wavefronts traversing in a parallel direction. However EAM in AF remains sensitive to technical limitations of bipolar electrograms. Furthermore, while electrogram patterns such as CFAEs may allude to drivers of AF, not all such waveforms appear to be pathological and may represent passive phenomena such as wavefront collision.