Abstract Body (Do not enter title and authors here): Introduction: Left atrial (LA) fibrosis identified by delayed enhancement MRI has been linked to poor outcomes post-AF ablation. We aim to assess the relationship between LA fibrosis and post-ablation AF burden in a persistent AF population.

Methods: This is a subanalysis from the DECAAF II trial which included persistent AF undergoing catheter ablation. Delayed enhancement MRI was performed up to 30 days pre-ablation. Fibrosis was quantified at a core lab and categorized into 4 stages: 1 (<10%), 2 (10%-<20%), 3 (20%-<30%), and 4 (≥30%). AF burden was defined as the percentage of time in AF post-ablation and was monitored using a 1-lead EKG device.

Results: This analysis included 658 patients. After ablation, patients were followed, categorized by Utah stage as follows: 95 in stage I, 380 in stage II, 271 in stage III, and 69 in stage IV. The mean (SD) AF burden during the blanking period (0 to 3 months) was 0.15 (0.26) for stage I, 0.17 (0.26) for stage II, 0.22 (0.29) for stage III, and 0.29 (0.30) for stage IV (p<0.001). Post-blanking period (after 3 months), the mean (SD) AF burden was 0.13 (0.22) for stage I, 0.15 (0.21) for stage II, 0.19 (0.25) for stage III, and 0.27 (0.27) for stage IV (p<0.001).

Conclusion: A higher atrial fibrosis identified by delayed enhancement MRI was associated with increased AF burden post-ablation.