Utilization of steerable sheath improves the efficiency of atrial fibrillation ablation guided by robotic magnetic navigation compared with fixed‐curve sheath

Abstract Background The objective of this study was to assess the impact of steerable sheaths compared with fixed‐curve sheaths on the procedural outcomes of atrial fibrillation (AF) ablation guided by robotic magnetic navigation (RMN). Methods and Results In this retrospective case−control study, 110 patients scheduled for AF catheter ablation were enrolled and divided into two groups. Fifty‐five patients (paroxysmal, 70%) were treated with RMN‐guided ablation utilizing a steerable sheath and another 55 patients (paroxysmal, 70%) were ablated with RMN using a fixed‐curve sheath. Clinical characteristics were similar between the two groups. Compared with the fixed‐curve sheath group, the steerable sheath group procedure time (111.9 ± 25.2 vs. 90.4 ± 20.7 min, p < .001) and radiofrequency (RF) time (35.9 ± 9.0 vs. 30.5 ± 7.4 min, p < .001) were significantly shortened. Additionally, the navigation index was significantly improved (0.41 ± 0.06 vs. 0.48 ± 0.08, p < .001) in the steerable sheath group. By employing a large catheter loop for targeting the right pulmonary veins (PVs), the steerable sheath group significantly reduced the RF delivery time (15.0 ± 3.0 vs. 12.0 ± 2.1 min, p < .001) during right‐side PV isolation (PVI). However, total fluoroscopy time was similar between the two groups (5.6 ± 2.6 vs. 5.0 ± 2.0 min, p > .05). Acute PVI success rates were similar between the two groups. No major or minor complications occurred in either group. Conclusion Appropriate utilization of steerable sheath technology can improve the efficiency of AF ablation guided by RMN, primarily by reducing the total procedure and RF delivery times of right‐side PVI without compromising safety.


| INTRODUCTION
Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice and catheter ablation of AF aiming for pulmonary vein isolation (PVI) has emerged as the standard of care once an invasive treatment is indicated. 1,2 Solid evidence has demonstrated that robotic magnetic navigation (RMN)-guided AF ablation not only provides increased comfort and associated sustained patient focus for physicians but also has comparable efficacy, superior safety with less peri-procedural complications, and shorter fluoroscopy time when compared with manual catheter ablation. [3][4][5] The highly flexible shaft of the magnetic catheter allows for multiple omni-directional angles of approach. However, maintaining stable contact throughout the entire PVI procedure remains challenging, with adjustments to the sheath position and deflection during the procedure often required. Previous studies have shown that steerable sheath technology has emerged as a means to optimize catheter−tissue contact and improve catheter guidance into different cardiac structures beyond fixed-curve sheaths. [6][7][8] However, the utilization of steerable sheaths is associated with increased potential for complications given their rigidity and wider outer diameter, as well as significant incremental cost. Until now, there has been insufficient data on the advantages of applying steerable sheaths in RMN-guided AF ablation. The purpose of this study was to compare the procedural efficiency parameters, acute PVI success rate, and complication rate using steerable and fixed-curve sheaths during AF catheter ablation.

| Clinical characteristics
In this retrospective study, 55 patients AF refractory to at least one antiarrhythmic agent were ablated with RMN using a steerable sheath. We additionally identified 55 patients previously treated with RMN using a fixed-curve sheath, who had matching age, gender, and type of AF characteristics. All 110 patients were treated between January 2020 and May 2021. This study was approved by the institutional committee on human research. According to institutional guidelines, all patients provided written informed consent.

| Definition of procedural parameters of RMN-guided ablation
Procedure time was defined as the total time from the Navigant™ "Open Procedure" to the Navigant "Close Procedure" (in minutes).

| Statistical analysis
All continuous variables are expressed as mean ± SD. Two-tailed t tests were used to compare continuous variables and categorical variables were compared by use of the χ 2 test (or Fisher's exact if χ 2 test was inappropriate). A two-tailed p < .05 was considered statistically significant. All statistical analyses were performed using SPSS (IBM Corp.).
Baseline demographic and clinical characteristics of the two groups are detailed in Table 1. There were no statistically significant differences between the two groups.

| Ablation procedure outcomes
Procedural parameters are summarized in Table 2  To further assess the cause of optimized procedure parameters in the steerable sheath group, we compared the ablation of left and right PVs (LPVs and RPVs) between the two groups. On the left side, sheath positioning was similar in both groups. We slightly adjusted the curve of the steerable sheath to more directly orient the ablation catheter to the LPVs. Although utilization of the steerable sheath seemed to make the RF lesions more continuous in many cases, especially on the ridge side ( Figure 1A), there was no significant difference in RF delivery time (18.5 ± 5.4 vs. 20.9 ± 6.0 min, p > .05) during ablation of the LPVs between the two groups.
When ablating RPVs using a fixed-curve sheath, the catheter could become unstable in locations such as the inferior aspect of the right inferior PV (RIPV) and the carina between the upper and lower RPVs ( Figure 1A). To better target the right PV ostia, the ablation catheter along with the steerable sheath was formed as a large loop inside the LA ( Figure 1B) Figure 1C).

| Acute procedural success and complications
Acute procedural success did not differ significantly between the two groups (steerable sheath 100% vs. fixed-curve sheath 100%). There were no minor or major complications observed in either group.

| Main findings
In this study, we reported our initial experience of steerable sheaths used in AF ablation guided by RMN. Compared with the fixed-curve sheath group, the mapping time and ablation time were significantly reduced in the steerable sheath group. Our observation is that this was likely due to improved catheter stability as evidenced by the improved navigation index, thereby shortening procedure time.
Right-side PVI was faster and RF delivery time was shorter when a steerable sheath was used. Comparable acute success and safety performance were seen between the two groups.

| Advantages of RMN-guided ablation
When compared with manual-guided navigation, RMN-guided catheter ablation in AF offers the advantages of precise and flexible catheter navigation, reduction in peri-procedure complications, and fluoroscopy exposure. 11,12 In this study, the total procedure time of all patients was shorter than that reported in our recent article, 13 which showed that procedure time decreased along the learning curve from 2010 to 2019. Moreover, all data in this study were derived with the thirdgeneration RMN system (Niobe ES), providing faster magnetic field direction changes than the Niobe II system, thus reducing procedure and RF times during AF ablation. 14 Other contributing factors could be the greater percentage of paroxysmal AF patients and smaller LA volumes than those reported in our previous study. 15 Strong evidence suggests the predictive value of catheter-tissue contact for the depth of ablation lesions. Compared with conventional sheaths, the utilization of steerable sheaths in ablation has been confirmed to increase catheter stability and tissue contact, thus improving ablation outcomes. 7,8,11 Contact force (CF) sensing technology is not available with RMN, but the "Magnetic Torque Meter," which measures the angular difference (0−90°) between the applied magnetic field direction and current catheter tip orientation, can be considered a  Figure 1). However, the RF delivery time was not significantly reduced in this area. When ablating RPVs, we regularly advanced the sheath laterally and superior inside the LA, and then pointed septally to form a large loop for targeting RPVs (Figure 1). Thus, a longer length of magnetic catheter is available with all three catheter magnets outside the sheath, providing omni-directional steerability and stable contact. With a fixed-curve sheath, we focus on optimizing transseptal puncture location to more easily access the RPVs, especially in patients with smaller atria. 19 We note that with the steerable sheath optimizing transseptal location for RPV access is less critical and this could be helpful for centers without intracardiac echocardiography available for transseptal access. When using the fixedcurve sheath, in some patients additional ablation points might need to be applied on the carina between the upper and lower PVs to achieve PVI after completion of the encircling line. However, the utilization of a steerable sheath could reduce the incidence of applying additional RF lesions on the carina, particularly during rightside PVI, thus decreasing RF delivery time (Figure 1).

| Study limitations
The major limitation of this study is that it is a nonrandomized retrospective case−control study in a single center. The patient population was matched by baseline characteristics and the ablation data were pooled from the same physician. These factors should have partially minimized bias from the nonrandomized design of this study.
However, a further prospective large-scale multicenter study is needed to confirm the effect of the utilization of steerable sheath technology with the RMN system.

| CONCLUSION
The utilization of steerable sheath technology with RMN for AF catheter ablation significantly reduced the procedure time, while achieving comparable acute success without compromising safety, when compared with the use of a conventional fixed-curve sheath.
Looping of the steerable sheath inside the LA facilitated right-side PVI navigation and reduced RF delivery time by providing more consistent, stable contact.

This study was supported by Clinical Research Plan for Shanghai
Hospital Development Center (SHD2020CR4096) (to Q. J.).