Catheter ablation of atrial fibrillation with a multi‐electrode radiofrequency balloon; first and early two centre experience in Europe

The Heliostar™ ablation system is a novel RF balloon ablation technology with an integrated three‐dimensional mapping system. Here, we describe our early experience and procedural outcomes using this technology for atrial fibrillation catheter ablation.


| INTRODUCTION
Pulmonary vein isolation (PVI) is the cornerstone for invasive treatment of drug refractory, symptomatic atrial fibrillation (AF), and is more successful at maintaining sinus rhythm than medical therapy. [1][2][3][4] The advent of single-shot technologies has ushered in a new era in AF ablation, targeting purely PVI usually as an initial procedure. Whilst radiofrequency ablation combined with a 3D mapping system was viewed as the gold standard technology for many years, cryoballoon ablation has emerged as the most frequently used alternative ablation technique for de novo PVI due to shorter procedure times and similar procedural outcomes facilitated by its single shot technology. 5 Recently, a RF balloon ablation system (Heliostar™, Biosense Webster) was introduced, combining single shot PVI catheter with an integrated 3D mapping system. The premarketing RADIANCE and SHINE studies demonstrated favorable safety and clinical outcomes at 12 months in early use. 6,7 This study aimed to assess the feasibility of the introduction of this technology into clinical practice, including acute procedural outcomes, workflows and comparing different sedation practices. The study cohort included patients who underwent first-time/ redo catheter ablation with drug-refractory paroxysmal or persistent AF. Written informed consent was obtained from all patients before the procedure and conducted in accordance with the Declaration of Helsinki. The Clinical Effectiveness unit registered and approved this study at each participating site (registration number 12381).

| Heliostar™ ablation system
The Heliostar™ ablation system encompasses a 28 mm compliant radiopaque balloon, 3Fr 15 mm circular mapping catheter (LASSOSTAR TM), 13.5Fr steerable sheath (Guidestar™) and a dedicated multichannel generator (nGEN™). The Heliostar™ balloon has 10 gold-plated electrodes with four irrigation holes and individual thermocouples to monitor tissue temperature throughout the procedure. A multipolar, non-nav mapping catheter, Lassostar™ provides both mapping and support, and integrates to the CARTO 3 system with Heliostar™ module to monitor/confirm the real-time pulmonary vein (PV) EGMs during ablation. Lasso Nav™ is used for initial geometry and voltage mapping.
Once the RF balloon is sited at the antra of each PV, the balloon is inflated and irrigated at a rate of 35 ml/min. Following apposition of the balloon to venous antrum, ablation energy is delivered in unipolar mode at 15 W with a temperature target of 55°C for 60 s. Optimal balloon positioning and ablation parameters before RF delivery is outlined in Figure 1. Anterior and posterior electrodes can be identified in the CARTO mapping system, and the electrodes adjacent to posterior segments can be selected to deliver ablation for 20 s ( Figure 1). Further ablation lesions can be customized to deliver circumferential or segmental ablation. Ablation electrodes provide impedance and electrogram data, and electrode temperature data is provided to the nGEN™ ablation. In all cases, the Heliostar™ module can display the realtime ablation parameters, EGM, inflation index and location of the catheter/balloon within the left atrial (LA) geometry ( Figure 2).

| AF catheter ablation
The procedure was performed under conscious sedation (CS) or general anaesthesia (GA). Both centers used a standardized approach for the procedure. SBH performed all procedures under CS except under specific clinical circumstances namely high body mass index, history of significant chronic respiratory disease or sleep apnoea (4 patients) where GA was administered. In comparison, all patients from UHZ underwent the PVI procedure with GA per institutional protocol.
Following the safe sedation protocol, CS was achieved with Midazolam and Diamorphine. All patients were on uninterrupted oral anticoagulation (Vitamin K antagonist or direct oral anticoagulant). Before the procedure, both centres used a multipolar oesophageal temperature probe CIRCA S-CATH™ was inserted. Patients undergoing CS procedures, local anaesthetic spray (xylocaine 1%) was liberally applied to the oropharynx following 1 mg Midazolam i.v. dosing. The lubricated probe was then passed posteriorly into the oesophagus whilst asking the subject to swallow, and the stylet retracted. The location was confirmed with X-ray. A warning alarm was set at 38°C followed by a maximal cut-

| Study outcomes
We systematically collected procedural metrics, including skin-to-skin

| Statistical analysis
The results are presented as absolute value with %, mean ± standard deviation (SD) or median and interquartile range (IQR). Normally distributed continuous variables were presented as mean (±SD) and non-normal distribution as median (IQR). Normally and non-normally distributed continuous variables were compared using student's t-test and Mann-Whitney U-test, respectively, whereas categorical variables

| Study population
A total of 60 patients, 72% male and 60% paroxysmal AF with a mean age of 64 (±8) years, underwent Heliostar™ balloon ablation. Fifty-six of these were a de novo catheter ablation procedure. The mean left ventricular function and LA diameter were 51 (±11) % and 42 (±7) mm, respectively, and the mean CHA2DS2-VASc was 2.1. Baseline characteristics and medical history of the study population are shown in Table 1.

| Procedural characteristics
Thirty-five patients (58%) underwent the procedure under CS. 235 out of 237 PVs were targeted (two veins remained isolated during the redo procedure), and acute electrical isolation was achieved in all targeted veins ( Table 2). One hundred and ten veins (48%) achieved electrical isolation with single shot circumferential RF application. Out of the remaining veins, 125 PVs required re-circumferential RF application to achieve isolation based on impedance and real-time EGM data

| Comparison of anaesthetic modality (CS vs. GA)
Both groups' mean procedure time and median RF applications per patient were similar (Table 3). Fluoroscopy time, time to isolation PV and observed acute reconnection rate were comparable. However, median RF application time was less in the CS group (CS: 5 min vs. GA: 7 min; p = .008), and the rate of PVs achieving first pass isolation was higher in

| Acute reconnection
PV entrance block was achieved in all veins; however, 17% of veins (40 PVs) demonstrated acute reconnection requiring further ablation to consolidate the lesion set ( Table 2). Out of the reconnected veins, 6 PVs were reisolated with segmental ablation (Figure 3). In multivariate analysis (first pass isolation, time to isolation, type of PV, LA dilatation, anaesthetic

| Ablation parameters for single shot isolation and acute reconnection-a subgroup analysis in the CS group
One hundred and fifty-two PVs were further analysed to compare PVs for single shot isolation (single shot vs repeat shot isolation) and for PVs that were reconnected to those were durably isolated within the CS group (acute PVR + vs. acute PVR −). Δ Temp-min during ablation was observed to have lower values in repeat shot isolation and Acute PVR + group compared to the counterpart and was statistically significant (p = .026 and p = .007, respectively). However, Δ Imp-min and TTI were comparable between the groups (Tables 5   and 6). Logistic regression analysis was performed, setting the outcome as the successful PV isolation with single shot RF application and the presence of acute PVR. In univariate analysis,

| Hospital admissions and early mortality-early follow-up data
There was no mortality within 30 days postprocedure. One patient required hospital admission to investigate chest pain postprocedure, but no significant findings were identified in cardiac investigations.

| DISCUSSION
In this study, we have described the early real-world procedural experience using the Heliostar™ RF balloon technology for AF ablation in two European, tertiary centres. We have shown that this technology Our experience has proved a short learning curve with Heliostar™ ablation and a procedure well tolerated under CS; furthermore we did not observe any "map shifts" during our experience, increasing the confidence of the utility of this technology with CS. In many jurisdictions, limitations on the use of GA or and is easy to measure. Therefore, close monitoring is required from the start of RF delivery. Simultaneously observing for diminished strength of the diaphragmatic excursion by palpation is an additional confirmation.
Heliostar RF balloon has the additional benefit of examining with bipolar pacing through the balloon electrodes before RF delivery to identify the proximity of the nerve. If phrenic nerve capture is noted with local pacing through the balloon, then this site can be avoided for RF or balloon repositioning could be considered.
Our initial data confirms a good safety profile and satisfactory acute success rate with a short procedure time under sedation.
Single-shot isolation rate has improved with learning curve dynamics, and minimum delta impedance drop was an independent predictor for the outcome. In addition, we have observed a higher rate of acute reconnection (17%) compared to the data published in RADIANCE and SHINE study (4.6% and 9.3%) with left-sided PVs and failing firstpass isolation as independent predictors. The learning curve effect should be subsumed when interpreting this data on acute PVR and the potential chances of transient PVI due to rapid workflow.
However, further prospective studies with follow-up are required to assess the durability of the lesions and the RF dosing and workflow optimization (such as optimal cut-off for minimum target). Therefore, it is prudent to recheck veins to ensure sustained isolation until further data are obtained from a larger cohort.

| LIMITATIONS
Our study reports the initial experience with this novel technology and the early outcomes may have an impact due to the initial learning curve. With the rapid development of other ablation technologies, more extensive randomized studies comparing currently available different single-shot technologies would be required to show the superiority of these novel technologies.

| CONCLUSION
Although the initial acute results are encouraging, long-term outcome data from a larger prospective study is required. Our early experience shows that novel Heliostar™ balloon ablation can be performed effectively, efficiently and safely under either GA or CS. Heliostar™ technology use pre-eminently stands out for rapid PV isolation time, low fluoroscopy dose and short learning curve even in the initial cohort.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

ETHICS STATEMENT
Obtained approval from the institutional Clinical Effectiveness unit to conduct the study (registration number 12381).