Po-01-151 degree of fibrosis remodeling alters atrial fibrillation inducibility

Mechanistically, the role of remodeled substrate in atrial fibrillation (AF) inducibility is not well understood. Here we assess the changes in AF reentrant-drivers (RDs) based on different levels of fibrotic remodeling – as visualized by degree of enhancement in late gadolinium enhancement (LGE) MRI. We compare the inducibility of the native fibrotic substrates in patients undergoing first-time ablation (FtA) and in those of repeat ablation (ReA) and characterize the regions most involved in RD maintenance. To investigate how different levels of fibrotic remodeling (enhancement in LGE MRI) affect AF inducibility. Ten LGE MRIs were obtained from AF patients undergoing FtA (n=5) or ReA (n=5). Fibrotic tissue was differentiated using personalized image intensity ratio (IIR) threshold; for scar, we used IIR=1.61; and the IIR for dense fibrosis was the midpoint between the two (Fig. 1B). For each patient, two personalized bi-atrial models were constructed: baseline and multi-level fibrosis. The baseline model includes only two tissue types – normal myocardium and fibrotic tissue; the multi-level fibrosis model for FtA has the addition of dense fibrosis, and for ReA, dense fibrosis and scar (Fig. 1C). Each model was tested for AF inducibility by rapid pacing from 40 uniformly distributed bi-atrial sites (Fig. 1D). RD-harboring regions were “cut out” (Fig. 1E) and the volumetric fraction of each substrate in each region was calculated (Fig. 1F). The ReA group had on average more remodeled tissue (29.11%) than the FtA group (20.05%). While the ReA group did not have more RDs than the FtA group, their RDs were more frequently inducible (from different pacing sites) compared to the RDs in the FtA group (usually inducible from just one pacing site). In general, one model was not found to be more arrhythmogenic than the other. For 7/10 patients, the model-pair produced at least one common RD. In all models, RDs required at least 30% of remodeled tissue within the local RD region. In ReA multi-level fibrosis models, RD-harboring regions had tissue significantly more remodeled (72.34%) than RD-harboring regions in baseline models (36.59%; p<0.0001). Different levels of fibrotic remodeling result in different levels of AF inducibility. These insights might be important in predicting ablation targets in AF patients.