A new basket player on the court: pulsed field ablation with a balloon-in-basket system for atrial fibrillation

Catheter ablation has become a cornerstone in the management of atrial fibrillation (AF), offering an effective rhythm control strategy for patients with drug-refractory disease.¹ While thermal ablation techniques—radiofrequency (RF) and cryoablation—have demonstrated strong clinical outcomes, they are associated with procedural limitations, including the risk of collateral damage to surrounding structures such as the oesophagus and phrenic nerves, as well as the potential to induce pulmonary vein stenosis.¹ Pulsed field ablation (PFA) has emerged as a novel, non-thermal alternative, with the potential to deliver precise myocardial ablation while minimizing adverse effects.²

Among the latest advancements in this field is the balloon-in-basket PFA system, which integrates electroanatomic mapping and contact sensing to optimize procedural efficiency and lesion durability. In this issue of Europace, Tilz et al.³ in the VOLT CE Mark Study presented the first human evaluation of this novel balloon-in-basket PFA system designed for pulmonary vein isolation (PVI). This prospective, multi-centre trial enrolled 150 patients with paroxysmal AF (PAF) and persistent AF (PersAF), evaluating the safety and 6-month effectiveness of this new ablation technology. The study demonstrated high acute success (99.1% PVI rate) and low serious adverse event incidence (2.7%), reinforcing the potential of PFA as a safer alternative to traditional thermal ablation. The rate of freedom from documented atrial arrhythmias was 88.2% in PAF patients and 76.7% in PersAF patients (freedom from symptomatic recurrence was documented in 90.2% of PAF patients and 74.4% of PersAF patients) through 6-month post-index procedure.

The reporting of outcomes for a novel technique is welcomed, and therefore, the authors should be commended for their work. Compared to other major trials investigating PFA, the VOLT results align well with existing evidence. The ADVENT trial,⁴ using a pentaspline PFA catheter, demonstrated 73.3% freedom from arrhythmia at 1 year for PFA, confirming noninferiority to conventional thermal ablation while maintaining a low serious adverse event rate of 2.1%. The AdmIRE trial,⁵ using a variable-loop PFA catheter, reported 74.6% freedom from arrhythmia at 12 months, with an adverse event rate of 2.9%, highlighting a similar safety profile. Meanwhile, the PULSED AF pivotal trial,⁶ using a circular array catheter, showed 66.2% success at 1 year for paroxysmal AF and 55.1% for persistent AF, with the lowest primary safety event rate of 0.7%. While the acute early effectiveness is encouraging, the long-term durability of this balloon-in-basket PFA system remains uncertain, particularly when compared to other PFA devices that have reported 12-month outcomes in their validation trials. AF is known to be a progressive disease, and recurrences often manifest beyond the 6-month mark. Notably, recurrence rates tend to increase over time, even in patients with PAF, highlighting the need for longer-term follow-up to assess the durability of ablation outcomes.⁷ Therefore, extended follow-up data will be essential to determine how the balloon-in-basket PFA system performs relative to these established trials.

Among the notable features of this balloon-in-basket PFA system is its contact-sensing capability fully integrated into an electroanatomic three-dimensional mapping system. This distinguishes it from other one-shot PFA devices designed for PVI, except for the circular catheter studied in the AdmIRE trial, which also features an integrated mapping system and tissue proximity indicator. Additionally, the updated version of the pentaspline catheter incorporates mapping functionality and catheter visualization, allowing operators to estimate contact based on spline deformation within the mapping system. While this provides an indirect indication of contact, no validation trials are yet available. The importance of catheter-tissue contact in PFA lesion formation has been highlighted in preclinical studies using vegetal and animal models, as our research groups have demonstrated.^8,9 These studies confirm that greater contact not only leads to deeper and more contiguous lesions but also plays a crucial role in ensuring effective and durable PVI. The integration of contact-sensing capabilities in modern PFA catheters, such as the balloon-in-basket system evaluated in the VOLT study, may enhance lesion durability and improve long-term outcomes by ensuring effective lesion formation and minimizing gaps in PVI. Additionally, the integration of mapping features is beneficial in reducing the need for catheter exchanges, which can be associated with potential unnecessary risks.¹⁰ Using a dedicated mapping catheter within the same larger sheath might increase the risk of bubble formation and stroke, although this has not been clinically demonstrated with PFA. Furthermore, the incorporation of mapping capabilities may also contribute to a reduction in overall fluoroscopy time, enhancing operator safety.

While the balloon-in-basket PFA system offers notable advantages, certain caveats should be considered. One limitation is its balloon shape, which is primarily designed for PVI and may not be as suitable for persistent AF patients who could benefit from more extended ablation strategies, such as posterior wall isolation—yet the authors performed PVI-only procedures in this trial. This limitation is not unique to this system, as similar concerns were raised with cryoballoon or laser balloon ablation, which were designed for PVI-only procedures. Although there have been reports of posterior wall ablation using cryoballoon, this approach may introduce unnecessary complexity, particularly when other PFA devices with more adaptable designs are now available. Indeed, other PFA catheters with different structural designs have already demonstrated potential for targeting non-PV sites.^11–13 These alternative designs may allow for more versatile lesion creation, which could be particularly relevant in patients with more advanced atrial disease.

One notable aspect of the VOLT trial design is its 90-day blanking period, which differs from the newly recommended 60-day blanking period per the 2024 EHRA guidelines.¹ This discrepancy arises because the VOLT study was designed and initiated before these updated guidelines were published. A shorter blanking period is now advocated to better capture true procedural success, reducing the potential for confounding from transient early recurrences. Findings from other PFA studies on the variable-loop circular catheter and the pentaspline catheter, suggest that earlier recurrences within the blanking period strongly predict late recurrences, questioning the necessity of maintaining a prolonged blanking period. In the AdmIRE trial,¹⁴ early recurrence (ER) within the first two months was a strong predictor of late recurrence (LR), with 87.0% of patients experiencing LR if they had ER within the first two month. Similarly, Mohanty et al.¹⁵ reported that all patients with ER in the second or third month after PFA with the pentaspline catheter experienced LR, leading the authors to propose that a 1-month blanking period might be sufficient after PFA, given that it does not induce significant inflammatory responses like thermal ablation. Although the 2024 EHRA guidelines advocate for a 2-month blanking period, this recommendation is based largely on data from radiofrequency and cryoballoon ablation rather than PFA-specific evidence. Future studies should explore whether a 1-month blanking period is sufficient to assess durable efficacy, aligning with growing evidence from recent PFA trials.

Lastly, while the study provides strong mid-term efficacy data, the role of antiarrhythmic drugs (AADs) in maintaining sinus rhythm remains an important consideration. Not all patients were completely off AADs after the 3-month blanking period, making it difficult to determine the true efficacy of the ablation procedure alone. The authors partially addressed this issue with a supplementary analysis that stratified outcomes based on AAD discontinuation. Among PAF patients who discontinued all Class I/III AADs post-blanking, 89.7% (78/87) remained free from atrial arrhythmias at 6 months, compared to 81.3% (13/16) in those who continued AADs at some point post-blanking. For PersAF patients, 84.4% (27/32) were free from recurrence off AADs, whereas the rate dropped to 54.5% (6/11) among those who used AADs at any time post-blanking. These findings suggest that AAD continuation influences reported efficacy rates. The overall freedom from documented atrial arrhythmias in VOLT (88.2% for PAF and 76.7% for PersAF patients) is notably higher than the recurrence-free rates reported in patients who were off AADs post-blanking. This discrepancy suggests that the true stand-alone efficacy of the ablation procedure may be lower than initially perceived. While the use of AADs is largely justified, particularly in cases of early recurrence during the blanking period, their influence on reported outcomes in this study should be considered. Given the relatively small patient cohort and short follow-up duration, the results may not fully capture long-term efficacy. Notably, maintaining patients off AADs in the first six months post-ablation is generally more feasible in real-world clinical practice, further highlighting the need for longer-term data to provide a clearer assessment of procedural success.

The VOLT CE Mark Study represents an important step forward in the evolution of PFA technology for AF ablation. The balloon-in-basket design, with integrated electroanatomic mapping and contact sensing, has demonstrated high acute success rates with a low rate of serious adverse events, reinforcing its potential in clinical practice. However, important questions remain, particularly regarding long-term durability. Given the relatively short follow-up period, further studies with longer-term outcomes and refined AAD stratification will be essential to accurately define the role of this next-generation PFA system in shaping the future of AF ablation. We welcome ‘VOLT’ as a new ‘Basket Player’ in the PFA portfolio.

Funding

This research received no funding.

References

Author notes