Abstract
Background
A new technology, the POLAR cryoballoon system, was designed to enhance maneuvering and stabilizing catheter positions with a softer balloon and more deflectable sheath. These novel characteristics may help achieve successful pulmonary vein (PV) isolation in difficult cases when conventional balloons were used.
Objective
This study aimed to investigate the differences in the lesion profiles, touch-up radiofrequency ablation (RFA) rate, and anatomical predictors of acute PV isolation between the POLAR and Arctic Front Advance Pro (AFA-Pro).
Methods
This retrospective study included 338 consecutive patients who underwent a first cryoballoon ablation for paroxysmal atrial fibrillation at Keio University Hospital from April 2019 to September 2023. Using propensity score matching, we extracted 135 pairs treated with a POLAR or AFA-Pro, compared the procedural outcomes, and explored the anatomical predictors related to successful PV isolations.
Results
In the matched cohort of 270 patients (median age 67 years [59–73], 77% male), 1535 cryoballoon applications were delivered for 1063 PVs, and touch-up RFA was performed for 84 PVs in 67 patients. The rate of touch-up RFA was significantly lower for the right inferior PV (RIPV) in the POLAR group (9.8% vs 21.6% P = .013), whereas there was no significant difference for the other PVs. A lower RIPV frontal angle was linearly associated with a more favorable outcome for the POLAR group than for the AFA-Pro group (interaction P = .0385).
Conclusion
The touch-up RFA rate for the RIPV was significantly lower in the POLAR group than in the AFA-Pro group, with a particularly pronounced difference for inferiorly oriented RIPVs.
Keywords: Anatomy, Atrial fibrillation, Cryoballoon ablation, Pulmonary vein isolation, Touch-up radiofrequency ablation
Graphical abstract
Key Findings.
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In a propensity-matched cohort of 270 patients who underwent first-time cryoballoon ablation, the touch-up radiofrequency ablation rate for the right inferior pulmonary veins (RIPVs) was significantly lower with the POLAR system (9.8%) than with the Arctic Front Advance Pro (AFA-Pro) system (21.6%).
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Post–cryoballoon ablation conduction gaps commonly remained at the bottom of the RIPVs in both groups; however, with the AFA-Pro balloon, the gap area tended to extend from the bottom toward the posterior region.
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The relative advantage of the POLAR system over the AFA-Pro system in achieving RIPV isolation was particularly significant in cases with inferiorly oriented RIPVs, especially when the RIPV frontal angle was less than −10°.
Introduction
Pulmonary vein isolation (PVI) with cryoballoon ablation (CBA) for paroxysmal atrial fibrillation (AF) has shown a comparable efficacy and safety to PVI using radiofrequency ablation (RFA).1 The initial CBA for symptomatic paroxysmal AF has been shown to reduce the recurrence and progression to persistent AF2, 3, 4, 5 and now is considered as a first-line therapy in the current clinical guidelines.6,7 Although cryoballoon technologies and unique techniques have been developed to achieve a complete PVI,8 conduction gaps requiring touch-up RFA sometimes remain at the PVs with anatomical difficulties, particularly for the right inferior PVs (RIPVs).9,10 Therefore, operators should consider several anatomical features related to difficult maneuvers for a complete PVI with CBA.11,12
A novel cryoballoon system, the PolarX and PolarX Fit (Boston Scientific, St. Paul, MN) has been designed to enhance maneuvering and stabilizing the catheter position by incorporating a softer balloon and more deflectable sheath than those in the conventional balloon, the Arctic Front Advance Pro (AFA-Pro) (Medtronic, Minneapolis, MN). Despite these design differences, most multicenter studies have reported a comparable efficacy in the PolarX and AFA-Pro systems.13, 14, 15 However, more data on the differences in the clinical outcomes between the 2 systems are needed to understand who may benefit from this novel cryoballoon system. Recently, a large prospective observational study suggested that the PolarX system was associated with a significantly lower touch-up RFA rate for an RIPV isolation.16 For further investigation, we evaluated the differences in the 2 systems, focusing on the acute procedural outcomes, lesion characteristics, and anatomical predictors of a successful PVI.
Methods
Study design
This retrospective study included 338 consecutive patients who had undergone a first CBA for paroxysmal AF at Keio University Hospital from April 2019 to September 2023. Using propensity score matching, we extracted 135 pairs treated with a PolarX or PolarX Fit (POLAR group) or an AFA-Pro (AFA-Pro group) and compared the procedural outcome and lesion characteristics. The POLAR group underwent cryoablation using a Polarsheath (15.5 F deflectable sheath), Polar X 28-mm balloon catheter or a PolarX Fit balloon catheter (adjustable to 28 or 31 mm), and Polar map catheter (8 electrodes, 20-mm loop diameter, and 3 F shaft diameter) whereas a FlexCath Advance (15Fr deflectable sheath), AFA-Pro 28-mm balloon catheter, and an inner lumen mapping catheter (Achieve, Medtronic) were used in the AFA-Pro group. The study was approved by the institutional review board of Keio University Hospital (approval number: 20200331). All patients provided written informed consent before the procedure, and an opt-out system was used for the use of clinical data in research. The research reported in this study adhered to the principles of Declaration of Helsinki.
CBA procedure
Patients underwent their procedure under deep sedation with propofol and were monitored using a bispectral index monitor (Aspect Medical Systems, Newton, MA), maintaining a value between 40 and 60. All procedures were performed with uninterrupted anticoagulation therapy, and heparin was infused to maintain an activated clotting time of > 300 seconds. A single transseptal puncture was performed using an RF needle (Baylis Medical, Inc, Montreal, QC, Canada) and an 8-Fr long sheath (SL0; St. Jude Medical, Inc, Little Canada, Minneapolis, MN). Cryoballoon applications were standardized for either 180 or 120 seconds added to the time to isolation for all PVs. If time to isolation was not achieved within 60 seconds, or if cooling was delayed, the application was stopped at the operator's discretion. In those cases, a repositioning of the balloon and a new freezing application were performed. When using a Polar Fit, a 28-mm or 31-mm balloon was applied to individual PVs at the operator's discretion. The esophageal temperature and compound motor action potentials were recorded in all cases. Diaphragmatic movement was monitored under phrenic nerve pacing during the cryoablation applications of the right superior PV (RSPV) and RIPV for the detection of phrenic nerve injury. Freezing was stopped immediately if excessive cooling occurred (< −60 °C for AFA-Pro, < −65 °C for POLAR), diaphragmatic contraction weakened (tactile feedback or reduced compound motor action potential), or esophageal temperature decreased.
Touch-up RFA
An acute PVI was confirmed using an inner lumen catheter by the disappearance of PV signals and indication of entrance block. In addition, high-resolution 3-dimensional (3D) mapping was performed at the operators’ discretion. If a PVI could not be achieved after ≥ 2 CBA applications, touch-up RFA was performed at the operator's discretion. Connection gaps were identified using a multipolar mapping catheter, and touch-up RFA was performed with an irrigated-tip catheter.
Outcomes and follow-up
The differences in the procedural parameters, including the rate of touch-up RFA, were analyzed for each PV. To evaluate the lesion difference, each PV ostium was divided into 4 segments, and the distribution of the lesion gaps and prevalence of multiple gaps after freezing were compared in the 2 cryoballoon systems. Multiple gaps were defined as gaps extending over 2 segments. All patients underwent a clinical examination and a 12-lead electrocardiogram at 2 weeks, 3 months, and subsequently every 3 to 6 months. Holter monitoring was performed 3 to 6 months after ablation. Recurrence was defined as any documented atrial arrhythmia of ≥ 30 seconds > 3 months after the procedure.
Measurement of the anatomic features of the RIPV
To investigate the anatomical predictors associated with a successful RIPV isolation using 2 different cryoballoon systems, the following anatomical measurements of the RIPVs were obtained: (1) RIPV frontal angle, (2) RIPV transverse angle, (3) ovality index, calculated as the ratio of the maximal to minimal ostium diameters, and (4) RIPV height. The frontal and transverse planes were used to assess the respective orientation angles of the RIPVs. A strictly perpendicular plane to the ostium was determined using a reformatted adaptive plane and was used to measure the maximal and minimal diameters. The RIPV height was defined as the vertical distance between the bottom of the RIPVs and the noncoronary cusp, measured manually using coronal images. A computed tomography analysis of the anatomic measurements is described in Figure 1.
Figure 1.
Computed tomography analysis of the RIPV angle measurements. A: Assessment of the RIPV frontal angle: a frontal view showing the angle measurement between the orthogonal axis (green) on the RIPV ostial intersection line (blue) and the horizontal axis (red). B: RIPV transversal angle: a transversal view showing the angle measurement between the orthogonal axis (green) on the RIPV ostial intersection line (blue) and the vertical axis (red). C–E: Assessment of the RIPV ovality from the perpendicular view to the long axis of the RIPV. The crosshair on the RIPV ostium (yellow star) has been rotated to be perpendicular to the ostium of the RIPV in both the coronal and transversal images (C and D) to obtain a perpendicular view of the RIPV ostium (E). The maximum and minimum diameters were measured from this view. Ao = aorta; LA = left atrium; LAA = left atrium appendage; LV = left ventricular; RIPV = right inferior pulmonary vein.
Statistical analysis
Continuous variables are reported as the median and interquartile range or the mean and standard deviation. Categorical data are presented as frequencies and proportions. Propensity score matching was performed to balance the clinically relevant baseline characteristic variables between the 2 treatment groups. The propensity scores were calculated by a logistic regression model adjusted for the age, sex, body mass index, history of heart failure, hypertension, diabetes mellitus, strokes, history of antiarrhythmic drug use, left atrial dilatation, and a reduced ejection fraction. The balance was evaluated by standardized differences of all baseline covariates using a threshold of 0.1 to indicate an imbalance. Comparisons of the baseline variables and study outcomes were performed using t-test, Wilcoxon test, or χ2 test, as appropriate. Furthermore, we fitted a logistic regression model to the matched cohort using interaction terms between each RIPV anatomical variable and the treatment group (POLAR or AFA-Pro). Standard errors were computed using 1000 bootstrap replicates. To determine the optimal cut-off values of RIPV anatomical variables for predicting the relative effectiveness of the POLAR system, subgroup analyses of the touch-up RFA rate for the RIPV were performed using different cut-off points for each anatomical variable. Survival analysis was performed to evaluate whether the type of procedure (AFA-Pro or POLAR) had an impact on the occurrence of AF recurrence arising > 3 months after the procedure. The survival time was defined as the time starting from the date of the procedure to the occurrence of an AF recurrence or the most recent clinical evaluation (maximum February 2024). The survival curves for the freedom of recurrence were calculated by the Kaplan–Meier method and compared using a log-rank test. Two-sided P values of < .05 were deemed significant for all tests. Statistical analyses were conducted using R version 4.6.0 software (R Project for Statistical Computing, Vienna, Austria).
Results
Patient characteristics
In the matched cohort of 270 patients (median age 67 years [59–73], 23% women), a total of 1535 CBAs were delivered for 1063 PVs, and touch-up RFA was performed for 84 PVs in 67 patients. The baseline characteristics after propensity score matching are listed in Table 1. In the POLAR group, 21 patients (15.6%) were treated with a PolarX Fit balloon catheter (adjustable to 28 or 31 mm). In total, applications with a 31-mm sized balloon for the left superior PV, left inferior PV (LIPV), and RSPV were performed for 12 (8.9%), 1 (0.74%), and 12 (8.9%) patients, respectively. All RIPVs were treated with 28-mm balloon size applications. Multipolar mapping catheters were used to confirm the PVI in 184 patients (68.1%).
Table 1.
Patient characteristics
| Variables | AFA-Pro (n = 135) | POLAR (n = 135) | SMD | P-value |
|---|---|---|---|---|
| Demographics | ||||
| Age y, median [IQR] | 69.0 [58.0–74.0] | 65.0 [59.0–72.0] | 0.076 | .203 |
| Women, n (%) | 31 (23.0) | 31 (23.0) | <0.001 | 1 |
| BMI kg/m2, median [IQR] | 24.3 [22.3–26.1] | 23.6 [22.1–25.5] | 0.026 | .474 |
| Medical history | ||||
| Heart failure, n (%) | 11 (8.1) | 10 (7.4) | 0.028 | 1 |
| Hypertension, n (%) | 68 (50.4) | 66 (48.9) | 0.03 | .903 |
| Diabetes, n (%) | 17 (12.6) | 18 (13.3) | 0.022 | 1 |
| Stroke, n (%) | 6 (4.4) | 8 (5.9) | 0.067 | .784 |
| Hyperlipidemia, n (%) | 51 (37.8) | 52 (38.5) | 0.015 | 1 |
| Coronary artery disease, n (%) | 10 (7.4) | 4 (3.0) | 0.201 | .17 |
| Cardiomyopathy, n (%) | 6 (4.4) | 4 (3.0) | 0.079 | .747 |
| Antiarrhythmic drug use, n (%) | 51 (37.8) | 51 (37.8) | <0.001 | 1 |
| CHA2DS2-Vasc score, n (%) | 0.161 | .417 | ||
| 0 | 26 (19.3) | 21 (15.6) | ||
| 1 | 32 (23.7) | 41 (30.4) | ||
| ≥2 | 77 (57.0) | 73 (54.1) | ||
| Others | ||||
| LA diameter cm, median [IQR] | 3.8 [3.5–4.1] | 3.7 [3.4–4.0] | 0.234 | .13 |
| LA diameter >4.0 cm, n (%) | 43 (31.9) | 40 (29.6) | 0.048 | .792 |
| LVEF %, median [IQR] | 65.9 [63.2–71.6] | 65.9 [61.4–72.2] | 0.122 | .771 |
| LVEF <50%, n (%) | 4 (3.0) | 5 (3.7) | 0.041 | 1 |
| BNP pg/mL, median [IQR] | 43.0 [17.3–98.4] | 50.9 [26.2–98.4] | 0.124 | .248 |
| Common LPV, n (%) | 6 (4.4) | 5 (3.7) | 0.037 | 1 |
Values are presented as the median [IQR] or n (%).
BMI = body mass index; BNP = brain natriuretic peptide; CHA2DS2-Vasc = Congestive heart failure, Hypertension, Age ≥75 (doubled), Diabetes mellitus, Stroke/transient ischemic attack (doubled), Vascular disease, Age 65-74, and Sex category; IQR = interquartile range; LA = left atrium; LPV = left pulmonary vein; LVEF = left ventricular ejection fraction; SMD = standard mean difference.
Biophysical parameters
We analyzed biophysical parameters limited to ablations that were ≥ 120 seconds in duration (Supplemental Table 1). Lower nadir temperatures and longer thawing times to 0°C were observed for all PVs with the POLAR cryoballoon system than with the AFA-Pro. Balloon temperatures at the time of isolation were significantly lower in the POLAR group for all PVs except for the LIPV. However, no significant differences in the time to isolation were observed between the 2 groups for any PV.
Procedural and clinical outcomes
The procedural outcomes for each vein are listed in Table 2. Although the procedural outcomes did not differ significantly for the left PVs, CBA using the POLAR system for the RIPV exhibited a shorter freezing time (206 ± 75 seconds vs 187 ± 63 seconds, P = .024), higher single-shot success rate (51.5% vs 70.7%, P = .002), and lower touch-up RFA rate (21.6% vs 9.8%, P = .013) than CBA using the AFA-Pro. Furthermore, the POLAR group required a greater number of applications (1.3 ± 0.6 vs 1.7 ± 0.9, P < .001) and longer freezing duration (179 ± 51 vs 211 ± 95, P = .001) for the RSPV. The single-shot success rate for the RSPV was significantly lower in the POLAR group than in the AFA-Pro group (81.2% vs 65.9%, P = .007), but there were no significant differences in the touch-up RFA rate between the 2 groups.
Table 2.
Procedural outcomes
| Pulmonary veins | Variables | AFA-Pro | POLAR | P-value |
|---|---|---|---|---|
| LSPV (259 PVs) | Cryoapplications | 1.4 ± 0.7 | 1.5 ± 0.8 | .269 |
| Total freezing time, s | 213 ± 72 | 215 ± 74 | .807 | |
| PV potential visible, n (%) | 119 (93.0) | 120 (92.3) | 1 | |
| TTI record, n (%) | 114 (88.4) | 114 (87.7) | 1 | |
| Single-shot success, n (%) | 100 (77.5) | 101 (77.7) | 1 | |
| Touch-up RFA, n (%) | 3 (2.3) | 5 (3.8) | .728 | |
| LIPV (259 PVs) | Cryoapplications | 1.5 ± 0.7 | 1.4 ± 0.5 | .572 |
| Total freezing time, s | 183 ± 69 | 172 ± 61 | .206 | |
| PV potential visible, n (%) | 95 (73.6) | 97 (74.6) | .971 | |
| TTI record, n (%) | 79 (61.2) | 91 (70.0) | .176 | |
| Single-shot success, n (%) | 93 (72.1) | 94 (72.3) | 1 | |
| Touch-up RFA, n (%) | 9 (7.0) | 9 (6.9) | 1 | |
| RIPV (267 PVs) | Cryoapplications | 1.6 ± 0.8 | 1.4 ± 0.7 | .057 |
| Total freezing time, s | 206 ± 75 | 187 ± 63 | .024 | |
| PV potential visible, n (%) | 80 (60.2) | 95 (71.4) | .07 | |
| TTI record, n (%) | 59 (44.0) | 88 (66.2) | <.001 | |
| Single-shot success, n (%) | 69 (51.5) | 94 (70.7) | .002 | |
| Touch-up RFA, n (%) | 29 (21.6) | 13 (9.8) | .013 | |
| RSPV (265 PVs) | Cryoapplications | 1.3 ± 0.6 | 1.7 ± 0.9 | <.001 |
| Total freezing time, s | 179 ± 51 | 211 ± 95 | .001 | |
| PV potential visible, n (%) | 113 (85.0) | 117 (88.6) | .483 | |
| TTI record, n (%) | 108 (81.2) | 108 (81.8) | 1 | |
| Single-shot success, n (%) | 108 (81.2) | 87 (65.9) | .007 | |
| Touch-up RFA, n (%) | 5 (3.8) | 7 (5.3) | .757 |
Values are presented as the mean ± standard deviation or n (%).
LIPV = left inferior pulmonary vein; LSPV = left superior pulmonary vein; PV = pulmonary vein; RFA = radiofrequency ablation; RIPV = right inferior pulmonary vein; RSPV = right superior pulmonary vein, TTI = time to isolation.
The distribution of the touch-up RFA sites is presented in Figure 2. In the AFA-Pro group, touch-up RFA was required in 39 patients (28.9 %): at the bottom of the RIPV in 22, at the posterior aspect of the RIPV in 19, and at the bottom of the LIPV in 5. In the POLAR group, 28 patients (20.7 %) underwent touch-up RFA: at the bottom of the RIPV in 13 patients, at the posterior aspect of the RSPV in 6, and at the bottom of the LIPV in 5. The most frequent gap site was the bottom of the RIPV in both groups. The reconnection of the posterior aspect of the RIPV was also frequent in the AFA-Pro group. The rate of multiple gaps at the RIPVs was significantly higher in the AFA-Pro group than the POLAR group (12.0% vs 3.0%, P = .011).
Figure 2.
Distribution of the touch-up radiofrequency applications required in the AFA-Pro and POLAR groups. LSPV = left superior pulmonary vein; RIPV = right inferior pulmonary vein; RSPV = right superior pulmonary vein.
The Kaplan–Meier survival curves for the AFA-Pro and the POLAR groups are shown in Supplemental Figure 1, and there were no significant differences between the curves (log-rank P = .46). One year after the procedure, 89.9% (84.9%–95.3%) in the AFA-Pro group and 87.2% (81.4%–93.5%) in the POLAR group were free of any AF recurrence.
Anatomical factors associated with touch-up RFA for the RIPV
To identify patients in whom the POLAR balloon was relatively effective for RIPV isolation, we compared RIPV anatomical variables in the patients who did and did not require touch-up RFA per study group (Table 3). In the AFA-Pro group, the RIPV was significantly more inferiorly oriented among the patients requiring touch-up RFA than among those not requiring touch-up (−16.7 ± 9.4 vs −7.2 ± 10.3, P < .001). In the POLAR group, the ovality index of the patients requiring touch-up RFA was significantly higher than that of the patients not requiring touch-up (1.77 ± 0.55 vs 1.49 ± 0.46, P = .04). Figure 3 shows the relationship between the anatomical variables and the touch-up RFA rate for the RIPV in AFA-Pro and POLAR groups. A lower RIPV frontal angle was linearly associated with a more favorable outcome for the POLAR system than for the AFA-Pro system (interaction P = .0385) (Figure 3A). For every 1° increase in the RIPV frontal angle, the odds ratio for the POLAR-to-AFA-Pro cryoballoon system increases by approximately 9.7% (Supplemental Table 2). At RIPV frontal angles between approximately −10° and −8°, the upper limit of the 95% confidence interval exceeded 1, indicating no significant difference in touch-up RFA rates between the 2 cryoballoon systems. Subgroup analysis suggested that the lower odds ratio associated with the POLAR system than with AFA-Pro was more pronounced in patients with an RIPV frontal angle of less than −10° (interaction P = .0457) (Figure 4). No significant interaction was observed between the other anatomical variables and the relative touch-up RFA rate of POLAR vs AFA-Pro (Figure 3B–3D, Supplemental Table 2).
Table 3.
Anatomical measurements of the RIPVs in patients who did and did not require touch-up RFA per study group
| Variables | AFA-Pro |
P-value | POLAR |
P-value | ||
|---|---|---|---|---|---|---|
| Touch-up (n = 29) | No touch-up (n = 105) | Touch-up (n = 13) | No touch-up (n = 120) | |||
| Frontal angle (°) | −16.7 (9.4) | −7.2 (10.3) | <.001 | −10.1 (8.0) | −8.4 (9.5) | .522 |
| Transversal angle (°) | 113.1 (9.9) | 116.8 (10.3) | .083 | 116.1 (10.7) | 115.6 (11.5) | .872 |
| RIPV height (mm) | 10.7 (18.0) | 13.3 (15.4) | .45 | 10.2 (19.2) | 10.3 (16.7) | .986 |
| Ovality index | 1.46 (0.34) | 1.46 (0.41) | 1 | 1.77 (0.55) | 1.49 (0.46) | .040 |
RFA = radiofrequency ablation; RIPV = right inferior pulmonary vein.
Figure 3.
Association of the anatomical parameters with the comparative effectiveness of the POLAR and AFA-Pro for the RIPV isolation. RIPV = right inferior pulmonary vein.
Figure 4.
Subgroup analysis for the rate of touch-up RFA stratified by RIPV frontal angle. CI = confidence interval; RFA = radiofrequency ablation; RIPV = right inferior pulmonary vein.
Complications
In total, 7 transient phrenic nerve palsies were observed: 3 (2.2%) in the AFA-Pro group and 4 (2.9%) in the POLAR group. In the AFA-Pro group, 1 occurred during an RSPV application and 2 during RIPV applications. In the POLAR group, all cases occurred during RSPV applications. Moreover, esophageal ulcers were observed in 1 patient treated with the AFA-Pro system. No cases of cardiac tamponade were reported in either group.
Discussion
The main findings of the present study were (1) the rate of touch-up RFA for the RIPVs was significantly lower in the POLAR group (9.8%) than in the AFA group (21.6%); (2) the connection gaps after CBA frequently remained at the bottom of the RIPVs in both groups, but the gap area was likely to extend from the bottom to the posterior regions in the AFA group; and (3) the relative benefit of the POLAR system vs AFA-Pro for the RIPV isolation was significant for inferiorly oriented RIPVs, especially when the RIPV frontal angle was less than −10°. The strength of our study lies in the detailed lesion analysis and exploration of the anatomical predictors for connection gaps, which may aid in selecting the cryoballoon systems.
The POLAR system, with its deflectable sheath and softer balloon, allows higher compliance to the PV and reaches lower balloon temperatures.17 Previous studies have reported comparable procedural parameters and long-term outcomes of the POLAR balloon to those of the AFA-Pro.13, 14, 15 Consistent with these findings, the POLAR group in our Japanese cohort exhibited lower freezing temperatures than and a similar rate of atrial tachycardia recurrence to those in the AFA-Pro group. However, a notable difference in procedural outcomes for the right PVs was suggested between the 2 systems (Table 2). The rate of a single-shot isolation of the RSPVs was significantly lower in the POLAR group than in the AFA-Pro group. This may be attributed to the operators exercising caution regarding phrenic nerve injury. Several studies have suggested a higher incidence of phrenic nerve injury with the POLAR system, particularly during RSPV applications.15,16 In our study, the rate of phrenic injury with the POLAR system was relatively low, which may reflect the strict monitoring of diaphragmatic contractions. We found that the touch-up RFA rate was significantly lower in the POLAR group than the AFA-Pro group. Previous studies have reported that the rate of an acute PVI is 96% to 97% for the AFA-balloon18 and 96.2% for the POLAR.19 The high touch-up RFA rate in the present study could be explained by the Japanese insurance system, which allows the combined use of radiofrequency catheters and 3D mapping systems. Indeed, Tachibana and colleagues16 have previously reported a relatively high rate of touch-up RFA after CBA and the superiority of the PolarX balloon for the RIPV isolation from the Japanese multicenter data. Notably, 184 patients (68.1%) in our study underwent high-resolution 3D mapping to confirm a complete PVI. High-resolution 3D mapping after CBA may detect residual antral PV potentials, which could contribute to the high rate of touch-up RFA, particularly of the RIPVs.20,21 In our lesion analysis of the RIPVs, residual connection gaps with the POLAR were limited to the bottom, whereas those with the AFA-Pro were likely to extend from the bottom to the posterior region (Figure 2). That finding may suggest that the high compliance of the POLAR balloon improves the PV occlusion and balloon-to-tissue contact.
Previous reports have identified several anatomical characteristics inhibiting the efficacy of CBA with the conventional cryoballoon system.11,12,22,23 The RIPVs are difficult targets for creating a complete isolation.24 The RIPV frontal angle is reported to be a strong predictor of electrical reconnections in several reports.12,23,25 Specifically, an inferiorly oriented RIPV worsens the alignment between the balloon and PV ostium and causes inadequate cooling.12 However, the procedural performance of the POLAR balloon is consistent regardless of the anatomical difficulties.26 In line with this finding, we showed that an RIPV frontal angle of less than −10° was associated with favorable procedural outcomes of the POLAR compared with the AFA-Pro. One might hypothesize that a high degree of deflection of the Polar sheath would improve the alignment for inferiorly oriented RIPVs and a PV occlusion. Our findings suggested that evaluating the RIPV anatomies before procedures may be useful for selecting the cryoballoon system and achieving a successful PVI.
Limitations
The findings of this study should be interpreted in the context of several potential limitations. First, 15.6% of the patients in the POLAR group were treated with PolarX Fit balloon catheters, which have a high adaptability to challenging anatomies and potentially can affect the lesion formation.27 However, all applications with the PolarX Fit balloons for the RIPVs were performed with a 28-mm size. Thus, the study results regarding the RIPVs were not affected by the size adjustability of the PolarX Fit balloons. Second, the decision to perform touch-up RFA depended on each institution’s ablation strategy and the national insurance system. Therefore, our findings may not be fully generalizable to routine clinical practice. Third, given this was a single-center, retrospective study, residual and unmeasured confounding factors may have remained despite propensity score matching. Fourth, given the increasing use of pulsed field ablation, it would be valuable to evaluate ways anatomical characteristics influence CBA outcomes in studies directly comparing it with pulsed field ablation.
Conclusion
The touch-up RFA rate for the RIPV was significantly lower in the POLAR group than in the AFA-Pro group, with a particularly pronounced difference for inferiorly oriented RIPVs.
Disclosures
The authors have no conflicts to disclose.
Acknowledgments
The authors thank John Martin for his assistance with English language editing.
Funding Sources
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Authorship
All authors attest they meet the current ICMJE criteria for authorship.
Patient Consent
All patients provided written informed consent before the procedure, and an opt-out system was used for the use of clinical data in research.
Ethics Statement
The study was approved by the institutional review board of Keio University Hospital (approval number: 20200331). The research reported in this study adhered to the principles of the Declaration of Helsinki.
Footnotes
Supplementary data associated with this article can be found in the online version at https://doi.org/10.1016/j.hroo.2025.05.027.
Appendix. Supplementary Data
References
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