Immediate Block Is Not Stable Block: Early Mitral Isthmus Reconnection Despite Systematic Vein of Marshall Ethanol Infusion and Focal Pulsed Field Ablation With the Sphere-9™ Lattice-Tip Catheter
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Background
Durable mitral isthmus (MI) block remains challenging in patients undergoing persistent atrial fibrillation (PeAF) ablation. Recent data using direct vein of Marshall (VoM) epicardial recordings have shown that endocardial pulsed field ablation (PFA) does not consistently achieve transmural MI lesions and that initially suppressed epicardial conduction may recover over time. Whether systematic VoM ethanol infusion (VoM-EI) combined with focal PFA overcomes this limitation and provides stable acute MI block remains unknown.
Objectives
To assess the incidence, timing, and procedural implications of early MI conduction recovery after systematic VoM-EI followed by focal PFA using the Sphere-9™ lattice-tip catheter.
Methods
This prospective, single-center observational study screened 55 consecutive patients undergoing a first catheter ablation for symptomatic PeAF with planned MI linear ablation. VoM-EI was systematically attempted before left atrial access and was successfully performed in 51 of 55 patients (92.7%), who constituted the study cohort. The lesion set comprised wide- antral pulmonary vein isolation, left atrial roof-line ablation, and MI-line ablation, all delivered using the Sphere-9™ lattice-tip catheter integrated with the Affera™ mapping and ablation system. After confirmation of bidirectional MI block, conduction was systematically reassessed following a standardized 30-minute waiting period. The primary endpoint was early MI conduction recovery.
Results
Mean age was 70.3 ± 8.2 years, and 36 patients (70.6%) were men. Initial bidirectional MI block was achieved in 50 of 51 patients (98.0%). During the 30-minute waiting period, MI conduction recovered in 9 of 50 patients with initial block (18.0%; 95% CI, 9.8%–30.8%), at a median of 16 minutes (IQR, 10–20; range, 8–23). Six of these 9 patients (66.7%) required additional coronary sinus (CS) ablation to restore block. Bidirectional MI block was re- established in all patients with conduction recovery, resulting in a final block rate of 50 of 51 patients (98.0%). Median procedure duration was 82 minutes (IQR, 73–95), and no major procedural complications occurred.
Conclusions
Immediate bidirectional MI block was not synonymous with stable block. Despite systematic VoM-EI followed by focal Sphere-9™ PFA, MI conduction recovered during a standardized 30-minute waiting period in approximately one in five patients, with two thirds requiring targeted CS ablation. Recovery occurred as late as 23 minutes, supporting reassessment beyond a 20-minute observation window. These findings extend recent evidence of incomplete MI transmurality after PFA by showing that even after systematic epicardial substrate modification with VoM-EI, apparently successful acute block may remain unstable. A standardized waiting period with systematic reassessment and targeted interrogation of residual CS conduction may therefore be warranted. Systematic invasive remapping will be required to determine whether waiting-period–guided re-ablation translates into durable chronic MI block.
Abstract Figure
Central Illustration:Acute durability of mitral isthmus block after focal pulsed field ablation combined with first systematic vein of Marshall ethanol infusion. Systematic ethanol infusion followed by focal PFA with the Sphere-9™ lattice-tip catheter achieved acute bidirectional mitral isthmus block in 50 of 51 patients (98.0%). During a standardized 30-minute waiting period, conduction recovery occurred in 9 of 50 patients (18%), at a median of 16 minutes and as late as 23 minutes, and 6 of these 9 patients (66.7%) required targeted coronary sinus ablation. Final bidirectional block was achieved in 50 of 51 patients (98.0%), supporting systematic waiting-period reassessment after PFA-based mitral isthmus ablation.
