Patient-tailored low-voltage-guided ablation of atrial fibrillation: mid-term efficacy and safety of our initial experience using a novel ultra-low-temperature cryoablation system

Introduction: The ideal ablation strategy for patients with persistent atrial fibrillation (PersAF) is still debated. Ablation strategies aiming at ablation of electrically abnormal atrial regions in addition to pulmonary vein isolation (PVI) have been promising in recent randomized studies. A novel ultra-low-temperature cryoablation (ULTC) system might overcome the limitations of radiofrequency (RF) energy by more reliably creating transmural lesions.

Purpose: Aim of this study is to report acute and mid-term efficacy and safety of our initial experience in patients with AF using this novel ULTC System.

Methods: Patients scheduled for catheter ablation who - based on the ZAQ score - had a high likelihood of having left atrial (LA) low voltage zones (LVZ) in 3D-electronatomical mapping (EAM) underwent ablation with the ULTC system and represent the population of this study. Ablation procedures were performed under deep sedation. A detailed high-density LA 3D-EAM was created in sinus rhythm using a grid-like multi-electrode catheter. Bipolar LVZs were defined as at least 1cm² surface of bipolar voltage <0.5mV. In case of atypical flutter, activation and entrainment mapping were used to determine the arrhythmia isthmus. The ablation strategy consisted in PVI and linear ablation of the LVZs, transecting (if narrow) or isolating (if broad) the areas of abnormal signals, and anchoring these lines to electrically silent structures (PVs or mitral valve ring). Endpoints were electrical isolation (entrance- and exit-block) and block across ablation lines using differential pacing. Clinical and procedural data were prospectively collected and analyzed. Continuous variables are expressed as median values (and interquartile ranges). Holter-ECGs and 12-lead-ECGs were performed at 3, 6 and 12 months after ablation and in case of symptoms.

Results: From April to September 2023, 25 pts (10 female, 40%) were included (median age 73 [66-78] years, median CHA₂DS₂-VASc Score 3, computed tomography [CT]-derived left atrium [LA] volume index [LAVI] 69 [63.0-94.6] ml/m²). The median ZAQ-Score was 2. Patients were mostly treated for persAF (n=15) and/or atypical flutter (n=11), only 1 patient presented with paroxysmal AF. Fourteen pts received their 1^st LA ablation, while 4 patients were redos after RF ablation, and 7 were redos after cryoballoon PVI. Two experienced operators performed most of the procedures (24/25, 96%). LVZs were detected in 22 patients (88%), 21 of these underwent PVI if needed (n=15), and LVZ-ablation (2 pts posterior wall isolation [PWI], 7 pts roof-line and anterior mitral-isthmus line [aMIL], 12 pts PWI and aMIL), 1 patient underwent just aMIL, while the 3 pts without evidence of LVZs underwent only PVI. Procedure duration was 210 (135-270) min, and decreased over time (in the first 12 patients 260 (203.75-302.50) min to 190 (135-235) min (p=0.047). X-ray time was 3.7 (2.5-5.8) min, while X-ray dose was 52 (29-138) cGy/cm². Ablation time was 1271 (720-1434) s. PVI using the ULTC was achieved in 15/18 pts (83%), in the remaining 3 pts RF energy touch-up was needed to successfully isolate the PVs. Linear ablations and isolation of LVZs were always (41/41 in 22pts, 100%) successfully achieved with the ULTC. Except for 1 right phrenic nerve palsy, no major acute complications were observed. Post-procedural chest pain was not reported by any patient, in 1 patient mild pericardial effusion was detected and treated conservatively. During 48h post-procedural ECG-monitoring, no acute recurrence of sustained atrial arrhythmias occurred. At a mean follow-up of 173 (147-192) days for 23/25 pts (2 pts contacted, no ECG yet) 96% of the pts were in sinus rhythm while 1 pt experienced a recurrence of permanent AF (cardioversion on amiodarone not successful). Late complications did not occur except for 1 pt who experienced a stroke with a small intracranial bleeding 4 weeks after the procedure and recovered without sequelae.

Conclusions: This is the first report of patient-tailored low-voltage-guided AF-ablation using a novel ULTC system. Acute and mid-term efficacy were very good (95% of acute bidirectional block across lines, 96% of pts in sinus rhythm at 6 months). Procedure-duration decreased over time, indicating an initial learning curve. Acute and mid-term safety were reassuring, particular attention should be paid to phrenic nerve function when ablating the right PVs.

Figure. Example of bipolar LA voltage-maps before and after ULTC-ablation in a patient with PersAF and atypical flutter. Broad LVZs (bipolar voltage <0.5mV) were initially detected at the posterior and anterior wall of the LA. After ablation, LVZ-isolation was confirmed by loss of electrograms in sinus rhythm (grey- and red-colored areas in the voltage-maps) and exit-block by high-output pacing. The shadows of the ring-shaped cryoablation segment correspond to each energy application and demonstrate the strategy (“Olympic rings”) used to isolate the PVs, the posterior wall as well as the LVZ at the anterior wall in this specific patient. Bidirectional block across the anterior mitral-isthmus line (aMIL) was confirmed by differential pacing and was nicely depicted by converging activation vectors  on opposite sides of the line in sinus rhythm.