Introduction
While radiofrequency (RF) catheter ablation for atrial fibrillation (AF) is associated with acute pulmonary vein isolation (PVI) in over 90% of cases, long-term success of a single ablation for paroxysmal AF has been reported to be 69% at one year 1 and only 54% beyond three years 2. Long-term PVI success, defined by the reduced rate of AF recurrence, is largely driven by the durability, as well as continuity and transmurality of formed lesions3. Acute lesion assessment is based on impedance drop from baseline, change in electrogram amplitude or morphology, change in pacing threshold and/or real-time MRI, while overall procedural success is confirmed in terms of PVI. Durability of RF lesions has been associated with the amount of RF energy delivered. Insufficient RF delivery leads to PV reconnection and prolonged procedure times, while excessive RF application may lead to complications such as esophageal injury, atrial perforation, steam pops and coagulum formation4-6. The relative RF energy received by the tissue and, consequently, lesion quality, are dependent on consistent coupling between the ablation catheter tip and the target tissue4,7, which can be compromised by small inadvertent movements during the procedure 8. Efforts to improve catheter-tissue contact and stability include the use of high-frequency jet ventilation to minimize respiratory excursion, high rate pacing to regulate cardiac contractions, electroanatomic mapping to monitor catheter proximity and tissue contact, as well as sheath and catheter selection 9-14. Introduction of contact force (CF)-sensing ablation catheters has allowed real-time measurement of catheter-tissue contact to guide RF delivery and formation of more effective lesions 7. The use of CF-sensing catheters has reduced procedure time and fluoroscopy usage, and improved the 1-year AF recurrence rate by up to 12% compared to non-CF sensing catheters 15-17. The adoption of steerable sheaths in PVI procedures has not only improved catheter manipulation and access to target sites 14,18,19 but, also, improved procedural CF. In randomized studies, steerable sheaths significantly enhanced CF stability, facilitated mapping and ablation, reduced procedure times and improved procedural efficiency when compared to standard fixed curve sheaths 20. Improvements in CF using steerable sheaths were further noted in different locations in the left atrium (LA). While accessing the left superior and inferior pulmonary veins requires a relatively straight sheath trajectory, the right superior and inferior pulmonary veins require greater sheath manipulation with tight angles of curvature and stabilization to maintain catheter tip position at the desired location 14. Steerable sheaths have also been shown to have fewer lesions with insufficient tissue CF15,21; the reduction of these poor CF lesions has been associated with improved freedom from recurrence at one year21. In an effort to optimize catheter stability during PVI procedures, the present study compares whether CF and procedural efficiency can be further improved using different commercially-available steerable sheaths.