Reversible pulsed field ablation for facilitating safe and effective mitral isthmus block: a case series

Background and Purpose

Posterior mitral isthmus (MI) block can be employed for ablation of persistent atrial fibrillation or perimitral flutter. However, achieving effective and lasting MI block can be difficult due to anatomical and morphological factors that favour the persistence of epicardial connections across the block line. A combined endocardial-epicardial ablation approach and the use of electroporation can increase efficacy while avoiding the risk of injury to extracardiac structures. This study aimed to evaluate the possibility of using reversible electroporation (PFrev) within the coronary sinus (CS) to precisely locate the epicardial ablation target and minimize the risk of coronary spasm

Methods

We report a case series of five patients (Tab. 1) with persistent atrial fibrillation and/or atypical atrial flutter referred for ablation using the AFFERA mapping system and the Sphere-9 catheter. Pulmonary vein isolation and/or additional linear ablation were performed according to the left atrial substrate. In all patients, after endocardial RF/PFA delivery along the MI line, residual conduction was observed, suggesting persistent epicardial conduction. PFrev was used within the CS (Fig. 1) to confirm the critical epicardial conduction site to exclude temporary ST-segment elevation on ECG. Once the site was confirmed, irreversible PFA was delivered.

Results

PFrev detected epicardial gaps in all patients, enabling complete MI block with irreversible PFA without repolarization abnormalities. A total of 12 ± 2.7 endocardial lesions (RF + PFA) were delivered at the MI, while 1.4 ± 0.9 irreversible PFA lesions were applied inside the CS. The total RF application time was 30 ± 15.2 seconds, and the total PFA time was 27.2 ± 24.1 seconds. Endocardial activation mapping confirmed bidirectional MI block after a 20-minute waiting period. No acute

complications occurred.

Conclusions

PFrev allowed precise localization of the conduction gap along the epicardial portion of the MI, enhancing both the efficacy and safety of irreversible electroporation. A combined endocardial–epicardial approach guided by PFrev appears to be a safe and effective method for achieving durable MI block.

Figure 1 Lesion setting (A). Activation map shows incomplete MI block, suggesting an epicardial conduction gap (B). Sphere-9 catheter within the CS at the MI level (C1). Pacing from the LAA reveals a complex EGM with far-field atrial signals and a high-frequency CS near-field potential. PFrev pulse results in temporary complete MI block, evidenced by the delayed activation of the second component of the double potential (C2). Within seconds, the second component gradually returns to baseline (C3).

AF, atrial fibrillation; CS, coronary sinus; EGM, electrogram; LA, left atrium; LAA, left atrial appendage; MI, mitral isthmus; PFA, pulsed field ablation; PFrev, reversible PFA; RF, radiofrequencyTable 1Figure 1