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.