Fehmi Keçe

Left Atrial Box Surface Ratio and AF-Recurrence 165 8 not in sinus rhythm after ablation an electrical cardioversion was performed. Entrance block in the PV’s and the box lesion was confirmed using maximal signal amplification. In addition, exit block from the box lesion was demonstrated by pacing with high output (10mA/2ms) at the posterior LA. PVI and box lesion isolation were reconfirmed ≥30 minutes after the last RF application. 8.2.3 Follow-up Follow-up at the outpatient clinic was performed in all patients at 3, 6 and 12 months after the procedure. Follow-up included clinical history for symptoms suggestive of recurrent AF, 12-lead Electrocardiography (ECG), 24 hour Holter monitoring and an exercise test (at 3 and 12 months). AAD’s were continued until the first outpatient clinic visit at 3 months. After this blanking period of 3 month, the AAD’s were stopped in all patients. Patients were encouraged to obtain ECG recordings in case of symptoms to determine recurrence. Recurrence was defined as any AF or atrial tachycardia (AT) on a 12-lead ECG or lasting > 30 seconds on Holter monitoring beyond 3 months. 8.2.4 Calculation of left atrial and box lesion surface areas The total LA surface area of all patients was measured on the segmented CT data after importing the original CT data into the CARTO system using the CARTO Merge software. The box lesion surface area, bordered by the posterior circumferential ablation lines adjacent to the PV ostia, the roofline and the posterior line was measured on the EA maps using dedicated software of CARTO and Ensite Velocity systems (figure 1). In addition, the ratio of the box lesion surface area to the total LA surface area (box surface ratio) was calculated. The distances between the contra-lateral pulmonary veins (box lesion width), between the roof and posterior line (box lesion height) and the distance between the middle of the posterior line to the mitral annulus was measured. Both in patients with and without atypical/mitral isthmus dependent flutter at follow-up, the distance between the posterior line and the mitral annulus was measured. For outcome comparison, the study subjects were divided into 2 groups according to the box surface ratio (above and below the median).