Correlation between AF substrate ablation difficulty and left atrial fibrosis quantified by delayed-enhancement cardiac magnetic resonance.

Background: Studies have shown that the presence of left atrial (LA) fibrosis can be assessed by LA delayed-enhancement cardiac magnetic resonance (LA DE-CMR) and may be predictive of outcome after ablation for atrial fibrillation (AF). We sought to test the hypothesis that the amount of LA fibrosis evaluated by DE-CMR correlates with the difficulty of complex fractionated atrial electrograms (CFAE) ablation. Methods: Twenty-two consecutive patients (86.4% nonparoxysmal AF) underwent substrate CFAE radiofrequency (RF) ablation (+/- Pulmonary veins isolation) with AF termination as the endpoint. LA DE-CMR was performed prior to ablation. A global index of DE was defined by an average of six LA segmental scores based on a four-grade scale (no enhancement to maximum enhancement). Time between first RF application and AF termination, and RF duration until AF termination, was recorded. CFAE area/total LA surface was also measured on CARTO maps (Biosense Webster, Diamond Bar, CA, USA). These measures served to evaluate ablation difficulty, and were correlated with CMR images by double-blinded analysis. Results: Ablation restored sinus rhythm in 20 of 22 patients (91%), with a time to terminate AF of 140 +/- 91 minutes. There was a significant correlation between the global averaged DE-CMR fibrosis grade and the electrophysiological substrate indexes such as "time to terminate AF" (Rho = 0.70, P = 0.0003), "RF duration until AF termination" (Rho = 0.65, P = 0.001), and a trend toward correlation with "CFAE area/LA surface" (Rho = 0.47, P = 0.03). Conclusions: LA DE-CMR can predict increased difficulty of CFAE ablation in AF. This tool may be beneficial in both selection of patients and ablation strategy. (PACE 2011; 34:1267-1277)