Pulmonary vein isolation (PVI) is the cornerstone therapy for atrial fibrillation (AF) ablation. However, in patients with non-paroxysmal AF and/or significant left atrial dilatation, results are often suboptimal and the best treatment strategy remains uncertain.1

In order to achieve lasting elimination of AF, many centers have suggested additional substrate ablation, particularly additional linear lesions or ablation of complex fractionated atrial electrograms (CFAEs).2,3 This approach has been questioned in a recent trial,4 but the failure of CFAE ablation to improve outcomes may in part be due to the shortcomings of current mapping algorithms, including limited temporal and spatial sampling.

Several studies have also reported the presence of focal rotors near or distant from pulmonary vein isolation sites. There is some evidence that ablation of this substrate could likewise increase AF-free survival.5 Although rotors and CFAEs have been suggested as possible therapeutic targets, their relationship and importance in the maintenance of AF remain to be established. The aim of this study was to assess the relationship between focal rotors and CFAEs in patients with AF, using a new four-dimensional (4D) electroanatomical mapping method to identify stable CFAEs.

The clinical characteristics of the 18 patients included are presented in Table 1. There were no serious complications related to the AF ablation procedure.

Rotors and complex fractionated atrial electrograms (Table 2)

A total of 44 rotors were identified, with a mean of 2.6±1.4 rotors per patient. Thirty rotors were identified in the left atrium and 14 were identified in the right atrium. The location of rotors in both atria is depicted in Figure 2.

Table 2.

Rotors and complex fractionated atrial electrograms: number and mean per patient.

	Number	Mean/patient
Rotors	44	2.6±1.4
All CFAEs	60	3.6±1.6
Stable CFAEs (grade 3)	39	2.2±1.5

CFAEs: complex fractionated atrial electrograms.

Figure 2.

Location of rotors in both atria.

(0.2MB).

A total of 60 CFAEs (39 CFAE grade 3) were identified, with a mean of 3.6±1.6 CFAEs per patient (mean number of grade 3 CFAEs: 2.2±1.5). Twenty-eight stable CFAEs were identified in the left atrium and 11 stable CFAEs were identified in the right atrium. The location of stable CFAEs in both atria is presented in Figure 3.

Figure 3.

Location of stable complex fractionated atrial electrograms in both atria.

(0.19MB).

Twenty years after the first pulmonary vein isolation procedure,6 the underlying mechanisms of AF maintenance remain essentially unknown, and the best ablation strategy remains to be determined. A recent trial4 showed that the two add-on strategies (linear and CFAE ablation) did not increase the success rate of pulmonary vein isolation. Our inability to fully understand the mechanisms of AF persistence and to increase the success rates of PVI may be related to inconsistent analysis of electrical activity in AF. Unlike other regular arrhythmias, AF cannot be mapped using a point-by-point strategy with a few ms of recording. A prolonged three-dimensional (3D) atrial mapping record is probably necessary to understand the underlying mechanisms of AF. To achieve these 4D maps (3D plus time), we adopted the CARTO electroanatomical system and recorded electrical activity with a basket catheter. This catheter is far from ideal due to heterogeneous contact, distortion and reduced steerability, but it does improve the quality of atrial maps compared to traditional catheters (point-by-point) or circular catheters (with limited atrial coverage).

CFAE ablation described by Nademanee et al.2 appeared to be effective in treating paroxysmal and persistent AF, but these results were not reproducible.4 Several factors may account for this failure, including different levels of experience and the lack of specificity and sensitivity of the electrogram recordings and mapping algorithms. Real CFAEs are sometimes difficult to differentiate from unstable electrical activity and far-field artifacts.7 We conceived the possibility of making prolonged records (>30 s) to detect repetitive complex electrograms and enable assessment of CFAE stability.

When studied in this way, only 65% of the CFAEs were shown to be stable according to our criteria. The determinants of CFAE stability are unknown, but we can hypothesize that more stable CFAEs could be a source for AF instead of far-field effects or transient fibrillatory activity.

We used the FIRM system to identify the presence of rotors that were anatomically located in the 3D atrial maps performed with CARTO. Rotors and CFAEs were frequently found in the same location within the atria. The spatial concordance between rotors and CFAEs was greater when only stable CFAEs were considered. The anatomical proximity between the two phenomena may signify that they are different manifestations of the same electrophysiological substrate, pinpointing zones of particular importance in the maintenance of AF. Still, a significant number of CFAEs and rotors are unrelated to each other, suggesting that they may be independent and/or that unstable CFAEs may be the result of far-field effects and that some rotors may be identified as such solely on the basis of subjective assessment of visual observation. Our results appear to contradict previous studies that were unable to show an anatomical relationship between rotors and CFAEs.8–10 This discrepancy could be explained by the novel method we used to identify stable CFAEs, for which prolonged periods of detection may be necessary.

Finally, if confirmed, these findings and mapping methods may improve our understanding of the underlying substrate of AF and assist physicians in the identification of appropriate ablation targets to improve clinical results.

Several limitations of this exploratory proof-of-concept study should be acknowledged. The small sample size precludes generalization to the overall population of patients with AF and makes subgroup analysis impracticable. The classification of CFAE stability was largely arbitrary and their relationship with rotors may have been impacted by the inherent subjectivity in the identification of the latter. Further studies will be required to confirm these findings and to assess the clinical impact of ablating substrate targets identified by this new mapping method.

Rotors and CFAEs are frequently found in the same location within the atria. The spatial concordance between rotors and CFAEs is greater when only stable CFAEs are considered. This relationship may have implications in the selection of appropriate substrate targets for ablation.

The authors have no conflicts of interest to declare.