Fehmi Keçe

Left Atrial Box Surface Ratio and AF-Recurrence 163 8 8.1 Introduction Wide circumferential pulmonary vein isolation (PVI) is the first step in atrial fibrillation (AF) ablation as the pulmonary veins (PV’s) and their antrum harbour the majority of triggers and are an important substrate for the maintenance of AF (1) . However, PVI alone in patients with progressively diseased atria has a poor outcome and additional ablation strategies may be required (2-5). Both histological and electrophysiological determinants of AF such as fibrosis, drivers and rotors are frequently found within the (inferior part of the) posterior wall of the left atrium, which may be explained by a common embryologic origin with the PV’s (6-10). Several studies have demonstrated that catheter ablation of the posterior wall in addition to PVI improves ablation outcome (11, 12). Similar, a surgical approach aiming to isolate the posterior wall resulted in 76% free of AF recurrences in patients with long standing persistent AF (13). The insertion of the PV’s in the LA can be highly variable between patients. A larger distance between the insertion of the superior pulmonary veins and inferior pulmonary veins increases the box lesion surface area. As the potentially arrhythmogenic posterior LA is not confined to the area between the PV’s but may extend caudally towards the coronary sinus (9, 10, 14), a variable part of the posterior LA will not be included in the box lesion, depending on the insertion of the inferior veins. In addition, with progressive left atrial dilation, the box lesion surface area as a ratio of total left atrial surface area may decrease further. We therefore hypothesized that differences in box lesion surface area normalized to total left atrial surface area may be an important factor influencing ablation outcome.