Functional mapping in recurrent atrial fibrillation: profiling the arrhythmogenic substrate

Abstract Background Recently, we found that employing short-coupled atrial extrastimuli revealed highly fragmented or double atrial evoked electrograms (EGMs) in atrial fibrillation (AF) patients, termed as hidden slow conduction (HSC). HSC sites were more prevalent among patients with persistent AF and were not consistently found within areas of complex EGMs during AF. Importantly, identifying HSC sites may provide insight into the early identification of the arrhythmogenic substrate, offering a potential target for ablation (1). Purpose Our pilot study aimed to assess the prevalence and distribution of HSC sites in patients with recurrent AF undergoing repeat ablation procedures, and to explore their correlation with low voltage areas (LVA), intramyocardial fat (inFAT), and left atrial wall thickness (LAWT). Methods All participants underwent pre-procedural multi-detector cardiac tomography (MDCT), processed with ADAS 3D LA™ software to generate 3D LAWT and inFAT maps (dense and admixture) as previously described (2). A LA voltage map was created using a contact-force ablation catheter and merged with the LA segmentation from the CT scan. Manual points after a triple extrastimulus from the right atrial appendage were acquired to fill all color gaps on the LA map using CARTO3 with an interpolation of 10 mm for the color threshold. HSC sites were identified by highly fragmented or double electrograms in response to triple extrastimulus, with normal or fractionated electrograms in sinus rhythm (figure 1). Results A total of 22 consecutive AF patients (41% persistent, 59% paroxysmal; AF duration 5.5±4.8 years) underwent HSC mapping, with an average of 44±11 sites tested per patient. The overall positive rate was 14.4% (138/959 sites), with HSC+ sites predominantly located in the septum and antero-septal wall (figure 2). HSC+ sites correlated with higher inFAT distribution (dense: 78.6% vs 39.6%, admixture: 88.7% vs 67.1%, both p<0.001) and lower voltage (0.8±0.4 mV vs 1.2±0.6 mV, p=0.03), but not with LVA (bipolar voltage<0.5mV) and showed no differences in LAWT. Segment 8 (septum) exhibited the highest fat infiltration (figure 2). Persistent AF patients had greater dense-inFAT concentration than paroxysmal (4.1% vs 4.7%, p=0.007). Conclusion HSC+ sites tend to align with areas of high inFAT distribution, indicating a fat-related structural remodeling that is more evident in persistent AF patients. This suggests that fat infiltration could play a role in AF progression. Additionally, inFAT infiltration may independently impact AF dynamics, potentially preceding the development of low-voltage scar areas.LA Segments and HSC sites illustration HSC+ and inFAT distrubution per segment