The complex fractionated atrial electrogram may be the sine qua non of atrial fibrillation, but qualitatively or quantitatively?

Abstract

Since its first description by Nademanee et al., numerous articles have appeared in the literature addressing the role and value of complex fractionated atrial electrogram (CFAE) on the effectiveness of atrial fibrillation (AF) ablation, with inconsistent results [1,2]. We read with great interest the article written by Junbeom Park and colleagues evaluating the relationship between the atrial substrate and the presence of CFAE prior to pulmonary vein isolation (PVI). They have compared left atrialwall thickness (LAWT), left atrial fat thickness (LAFT) and fat volume according to the presence of CFAE. They have used transthoracic echocardiographyand cardiac computed tomography in order tomeasure LAWT and LAFT and to define the anatomy of the left atrium (LA) before ablation. They have used cycle-length-based automated CFAE algorithm (EnSite NavX System, St. Jude Medical Inc., Minneapolis, MN, USA) to locate the CFAEs. They conclude that regions with CFAE in LA had thicker LA walls than those without CFAE, which was related to interatrial myocardial fibers and the anatomical raphe. Additionally, LAWT was found to be thinner in regions with CFAEs that disappeared after PVI as compared to those that remained (1.8 ± 0.6 vs. 2.1 ± 0.7 mm, p b 0.001), whereas LAFT did not show any significant differences after the ablation procedure. CFAEs that remained after PVI were related to thicker LAwalls and were usually located at the anterior superior wall, septum and LA appendage [3]. These results are really very important regarding guidance for the ablation approach in patients with persistent atrial fibrillation. However, there is a crucial point that we need to discuss in order to improve our understanding of CFAE. This study does not, as its methodology is not so oriented, provide a clear understanding of how ablation of thicker LAWT regions with CFAEs would influence the results of ablation. On the other hand, in a recent study by Han SW, it has been observed that the ratio of atrial mass reduction during CFAEguided ablation does not influence the efficacy of AF ablation [4]. Thus, taking these two studies together, we can speculate that, as thicker LAWT regions are ablated in CFAE-guided ablation, the greater amount of atrial mass reduction would not positively influence AF ablation results. This raises the question of whether the region of CFAE is a consequence of the anatomical quantity or the functional properties of the atrial tissue involved in the process. Recent studies have drawnattention to increaseddensity offibroblasts and interstitial tissue rather than the quantity of atrial tissue in areaswith CFAEs [5,6]. Probably as a result of the complexity involved in the definition of CFAE, there are serious inconsistencies among the reported results of CFAE-guidedablation studies.WhileNademanee reports success rates of 80–90% inCFAE-guidedablations in caseswithpersistentAF, other centers practicing CFAE-guided ablation by using different software or visualmethods have reportedmuch different success rates in the range of 30–40% [1,2,7]. It seems that the only important issue here is delicate detection and ablation of the critical substrate producing and sustaining AF, the sine qua non of atrial fibrillation. These critical substrates are ganglionic plexuses for some authors, regions of CFAE, empirically created rooflines or linear lesions involving anterior or posterior walls of the atriumor themitral isthmus for others. Another important issue here is to find which definition correctly defines regions of critical substrates in situations involving complex pathophysiological features like persistent AF. Since themore aggressive andwider the ablation, themore fibrosiswe leave behind, we need to find the best strategy to plan the best hit. To conclude, more comprehensive studies and consistent results are needed to define CFAE and its role in AF ablation. Studies reported to date do not seem to fill the gap in this issue. We probably need a consensus report to define the CFAE regions objectively, in terms of both the quantity and quality of the atrial tissue involved, and also multi-center clinical studies with appropriate methodological basis to clarify how ablation of these pathological areas affects the shortand long-term results of ablation of persistent AF.