Visualization of a novel tissue proximity indicator on a variable-loop pulsed field ablation catheter with intracardiac echocardiography

Key Teaching Points.

• ▪Adequate catheter-to-tissue contact is crucial for creating effective and durable lesions, even in pulsed field ablation. The novel tissue proximity indicator (TPI) with the VARIPULSE platform provides real-time, impedance-based feedback on catheter contact.
• ▪As demonstrated in this case, the TPI visualization (“Contact Clouds”) correlates accurately and in real time with physical contact confirmed by intracardiac echocardiography (ICE).
• ▪Using TPI allows for objective assessment of catheter contact, potentially enhancing procedural efficacy and safety, especially in areas where ICE visualization is challenging.

Introduction

Catheter-to-tissue contact is critical for creating durable lesions during pulsed field ablation (PFA).^1,2 PFA is a novel, nonthermal ablation modality that uses high-voltage electrical pulses to create irreversible electroporation, leading to selective myocardial cell death while preserving adjacent tissues such as the esophagus and phrenic nerve. Although this tissue-selectivity significantly enhances the safety profile of atrial fibrillation ablation, as demonstrated in the pivotal admIRE trial,³ the efficacy of lesion creation remains dependent on stable energy delivery, which requires adequate catheter-tissue contact.

Objective assessment of contact can be challenging. Intracardiac echocardiography (ICE) is considered the gold standard for real-time visualization of the catheter-tissue interface. For example, in anatomically complex locations such as the ridge between the left atrial appendage (LAA) and the left pulmonary veins, where stable catheter contact is challenging to achieve, objective visualization tools are paramount. However, its utility can be limited by its 2-dimensional nature and the difficulty of maintaining optimal views.⁴

The VARIPULSE platform (Johnson & Johnson MedTech, Irvine, CA), which uses a variable-loop circular PFA catheter, is fully integrated with the CARTO 3 system and features a novel tissue proximity indicator (TPI). A recent software update (V8.1 phase3) introduced a refined, impedance-based TPI algorithm providing real-time feedback on each electrode’s contact. Herein, we present a case that illustrates the clinical utility and visual correlation of this TPI with ICE during pulmonary vein isolation (PVI).

Case report

A man in his 70s with paroxysmal atrial fibrillation was scheduled for his first PVI procedure. The procedure was performed under conscious sedation using the VARIPULSE platform. Real-time visualization was guided by the CARTO 3 system and ICE.

During ablation at the ridge between the left superior pulmonary vein and the LAA, the TPI initially indicated a lack of contact for several electrodes (Figure 1A). This was confirmed by ICE, which showed a small gap between the catheter and the endocardium. Based on this feedback, no PFA energy was delivered. The catheter was carefully advanced a few millimeters until the TPI provided a clear positive signal, indicating firm apposition (Figure 1B). ICE confirmed stable and consistent tissue contact at this position, and a successful PFA application was then delivered.

Figure 1.

Visual correlation between the TPI and intracardiac echocardiography (ICE). A: No contact. At the ridge between the left atrial appendage and the left superior pulmonary vein, the TPI shows no “Contact Clouds” on the relevant electrodes. The corresponding ICE image reveals a clear gap between the catheter and the atrial tissue, indicated by the open arrowheads. The numbers displayed on the ICE image correspond to the specific electrode numbers on the catheter (also indicated on the CARTO map). B: Contact. After slight catheter advancement, the TPI displays purple Contact Clouds. ICE confirms firm tissue apposition, indicated by the solid arrowheads. TPI = tissue proximity indicator.

Furthermore, the real-time responsiveness of the TPI was demonstrated at the ostium of the right superior pulmonary vein, a location notoriously challenging to visualize clearly with ICE from the right atrium. As shown in the Supplemental Video, the video displays the CARTO 3 map with the TPI’s “Contact Clouds” on the left and the corresponding ICE image on the right. As the operator intentionally maneuvers the catheter to disengage it from the tissue, the green Contact Clouds instantly disappear, precisely at the moment ICE confirms physical separation. Conversely, upon re-engaging the tissue, the Contact Clouds reappear without any discernible latency. This dynamic visualization highlights the TPI’s high fidelity in tracking rapid changes in catheter contact status.

Discussion

This case report demonstrates the real-time, instantaneous correlation between the novel impedance-based TPI of the VARIPULSE catheter and direct visualization by ICE. The primary advantage of PFA is its ability to mitigate the risk of collateral damage to noncardiac structures. However, this safety benefit does not diminish the fundamental need for effective energy delivery to the target myocardium. Our case illustrates how the TPI can serve as a crucial tool to ensure this prerequisite is met. As demonstrated at the challenging LAA ridge, the TPI can guide catheter manipulation to optimize contact, potentially preventing ineffective energy applications and reducing the risk of complications from excessive catheter pressure.

Although ICE provides invaluable direct imaging, it is not without limitations. Procedurally, it requires an additional large-bore venous sheath, adding to the patient’s burden, and carries inherent risks such as pericardial effusion. Furthermore, it is an operator-dependent technique, and maintaining a stable, high-quality view of all electrodes on a circular catheter simultaneously is often impossible owing to its tomographic nature. The value of the TPI is particularly magnified not only in areas where ICE visualization is inherently limited, such as the right-sided pulmonary veins, but also in anatomically complex regions such as the LAA ridge where ensuring stable contact is the primary challenge. In this context, the TPI offers a significant advantage by providing continuous, objective feedback for the entire catheter loop. Our case suggests that TPI can serve as a reliable surrogate or, more powerfully, a complement to ICE, allowing for a more comprehensive assessment of catheter stability. Our clinical observation aligns with preclinical findings that demonstrate the impact of electrode-tissue contact and TPI on lesion depth and formation.^1,2 Furthermore, recent clinical data suggest a strong association between sites lacking TPI indication and acute pulmonary vein reconnection gaps.⁵ This underscores that ensuring adequate contact using TPI, as visually validated in our case, is critically important for achieving first-pass PVI success.

We acknowledge several limitations. This report is based on a single case, and its findings may not be generalizable. The ultimate impact of TPI-guided ablation on long-term clinical outcomes was not assessed.

Despite these limitations, this case highlights that the high-fidelity TPI of the VARIPULSE platform is a valuable tool for assessing real-time catheter contact. Further studies involving larger patient cohorts are warranted to validate the role of this technology in improving the long-term success rates of PFA for atrial fibrillation.

Disclosures

The authors have no conflicts of interest to disclose.