Fehmi Keçe

Chapter 1 18 1.3.5 Rotor ablation With focal impulse and rotor modulation (FIRM) ablation, local sources and rotors are targeted. In the CONFIRM trial the success rate was 85% in a mixed AF-population, compared to only 20% with conventional ablation (33). Despite the promising results, poor long-term outcomes with FIRM-guided ablation are reported with randomized clinical trials (37% at 18±7 months)(34). It could be argued that in FIRM-ablations the favorable outcomes are attributed to adjunctive PVI, however this is difficult to conclude given these studies are non-randomized. PVI remains the foundation of all AF catheter ablation, and FIRM guided ablation alone, has not been shown to be efficacious (34, 35). 1.3.6 Substrate ablation Substrate for AF may consist of fibrotic areas detected with MRI (DECAAF study)(36) or low voltage areas identified with voltage mapping. Yang et al. reported 70% AF-freedom after 30 months in patients who received additional substrate ablation compared to 51% who did not (37). Another novel ablation strategy is that of box isolation of fibrotic areas (BIFA) by Kottkamp et al. with success rate of 72% in patients with non-paroxysmal AF (38, 39). An interesting question is whether Delayed-Enhanced (DE)-MRI and voltage mapping both identify the same, potentially arrhythmogenic, atrial substrate. In a study of Chen et al. 61% of the low voltage areas co-located with DE-MRI and only 28% of the DE-MRI areas displayed low voltages (<0.5 mV). In this study the most arrhythmogenic sites co-located better with low voltage areas (78%) compared to DE on MRI (63%)(40). Arrhythmogenic sites were defined as spatio-temporal dispersion (potentially corresponding to rotational activity) or continuous activity. The authors suggest that further electrophysiological criteria should be used to guide ablation of arrhythmogenic substrate: late potentials, fractionated potentials, slow conduction areas, rapid/continuous activity or repetitive rotational activities with spatio-temporal dispersion during AF (40). 1.3.7 Posterior Box Isolation Especially in persistent atrial fibrillation other left atrial structures proved to play a role in the maintenance of atrial fibrillation(2). Histological and electrophysiological determinants (fibrosis, drivers, rotors) are often found in the posterior wall of the left atrium. This may be explained by the common embryologic origin of the pulmonary veins (41-45). Several studies showed that posterior wall isolation in addition to pulmonary vein isolation improves ablation outcome (46, 47). The surgical treatment of persistent atrial fibrillation ‘Cox Maze technique’ emphasize the role of the posterior wall and also promotes the use of the Box Lesion approach.