Substrate Modification Is a Better Predictor of Catheter Ablation Success in Atrial Fibrillation Than Pulmonary Vein Isolation: An LGE-MRI Study

OBJECTIVES: Outcomes of catheter ablation of atrial fibrillation (AF) vary widely. We used late-gadolinium enhancement MRI (LGE-MRI) to examine the relationship of ablation-induced scarring in the pulmonary vein (PV) region and overall atrium to evaluate the role of PV encirclement and substrate modification in predicting outcome of catheter ablation in AF. METHODS AND RESULTS: LGE-MRI was performed to quantify baseline atrial fibrosis, which was classified into four stages (stage I with fibrosis <10%, stage II with fibrosis 10–20%, stage III with fibrosis 20–30%, and stage IV with fibrosis ≥30%). Patients then underwent ablation and repeat LGE-MRI at three months to assess for ablation-induced scarring. PVs were studied to evaluate for complete encirclement with scar. Image processing was used to overlay the scar onto baseline fibrosis to assess the overlap and calculate residual fibrosis. A total of 172 patients were included with an average baseline fibrosis of 14.6 ± 8.4%. The average number of PVs encircled with scar at three months was 1.2 ± 1.3 with only 9% of patients having all four PVs completely encircled. The average residual fibrosis was 11.9 ± 7.3%. High residual fibrosis was defined as >10%. Recurrent AF was found in 60 patients (34.9%) over a follow-up of 346 ± 82 days. Baseline and high residual fibrosis were significant predictors of recurrence (hazard ratio [HR] of 2.2; P < 0.01 and HR of 3.2; P < 0.01, respectively). The number of PV encircled was not a significant predictor of recurrence. CONCLUSION: LGE-MRI of ablation-induced scarring demonstrates that chronic PV encirclement is rarely achieved. Procedural outcomes are better predicted by baseline atrial fibrosis and ablation-induced substrate modification.