EDITORIAL Identification of AF Drivers: Toward a Mechanistic Basis of AF Ablation

While the ablation endpoint in patients with paroxysmal atrial fibrillation (AF) has been largely standardized, the optimal approach for patients with persistent AF remains unknown. Among the latter, it is clear that pulmonary vein (PV) isola-tion alone is insufficient.1 In an effort to improve outcomes in patients with persistent AF, left atrial (LA) substrate modification has been shown to be effective.2,3 This may be accomplished by linear ablation and/or ablation of complex, fractionated electrograms (CFAEs). Although CFAEs may be markers of sites that are critical to the fibrilla-tory process, i.e., drivers, it is also possible that they represent passive phenomena as a result of wave collision, tissue anisotropy, and slow con-duction.4 Even if one uses a relatively stringent definition of a CFAE site, e.g., continuous electri-cal activity, the likelihood that ablation at such a site will have a favorable impact on the AF cycle length is modest.5 The fact that such sites may be found away from the PV region in patients with paroxysmal AF also suggests that they may be nonspecific.6 Also, a randomized study failed to show an incremental benefit of CFAE ablation in patients with persistent AF.7 Thus, it is possible that CFAE ablation results in more tissue destruc-tion than perhaps necessary to eliminate AF. This has important implications with regards to proce-dure times, complication rates, and atrial transport function. Prior Studies Using Multielectrode Catheters Clinical studies involving electrogram-guided ablation typically used an ablation catheter for mapping purposes.8 Obviously, the inability to map adjacent areas simultaneously makes it im-possible to distinguish between active and passive phenomena. In an attempt to overcome this limita-tion, several investigators have utilized multielec-trode catheters capable of recording over a larger surface area of the left atrium. Rostock et al.9 inves-tigated CFAE sites in patients with paroxysmal A