Fehmi Keçe

Left Atrial Box Surface Ratio and AF-Recurrence 173 8 8.4 Discussion 8.4.1 Main Findings The major finding of this study is that a larger box lesion surface area as a ratio of total left atrial surface area is protective for AF/AT recurrence after ablation for persistent atrial fibrillation. To the best of our knowledge, this is the first study that investigated box lesion surface area ratio in relation to ablation outcome. 8.4.2 Benefit of substrate modification beyond PVI The necessity of extending the ablation beyond PVI by performing substrate modification in patients with persistent AF is currently controversial due to the STAR-AF II trial, in which no benefit was demonstrated of additional ablation beyond PVI (18). Studies reporting on favourable outcome after isolation of the posterior wall are not in direct contradiction with the STAR AF II trial as this trial did not include a group undergoing isolation of a part of the left atrium in addition to PVI. Isolation of a part of the posterior left atrium may be a promising strategy, as there is evidence that the LA posterior wall harbours triggers and substrate for AF: animal studies have demonstrated that 80% of AF triggers are located in the posterior wall including the PV region, based on electrophysiological and molecular findings (19-21). In addition, imaging studies could demonstrate that fibrotic areas (atrial delayed enhancement) are mainly located in the posterior wall (6-8). More specific, the preferential distribution of drivers and atrial fibrosis, beside the PV-antrum, is located in the inferior part of the posterior wall (9, 10). The importance of targeting the posterior wall in patients with persistent atrial fibrillation is also demonstrated by the encouraging results (62% overall freedom of AF) of surgical ablation (22) of the posterior wall. In line with these results, we recently published a 76% success rate with a stand-alone surgical box lesion in persistent AF (13). A meta-analysis comparing catheter ablation of PVI vs. PVI with box lesion also showed a benefit of adding a box lesion to PVI in patients with persistent atrial fibrillation (11). In the current study, 1-year success was 40% after a single procedure off AADs and 64% after repeated procedures on/off AAD. Bai et al . recently reported an anti- arrhythmic drug free survival of 65%, 50% and 40% after respectively 1, 2 and 3 years follow up in persistent AF after catheter ablation of the posterior wall. (23). Lim et al. reported a 2-years AT/AF drug free survival of 53% in patients with persistent atrial fibrillation (24). The difference in outcome between surgical and catheter based isolation of a box lesion can be explained by the higher durability of surgical compared to catheter based ablation lesions (25). It is unknown if the area of the box lesion in patients undergoing a surgical box lesion is larger than patient undergoing catheter ablation.