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Feasibility and safety of left atrial posterior wall isolation with a new Cryoballoon technology in patients with persistent atrial fibrillation

Abstract Background Left atrial posterior wall isolation (LAPWI) is often performed in addition to pulmonary vein isolation (PVI) in the setting of persistent atrial fibrillation (AF) ablation. The aim of this study was to evaluate the feasibility and safety of a new cryoballoon ablation system in achieving PVI + LAPWI isolation. Methods The study was a prospective, non‐randomized, single center study. Forty consecutive patients, undergoing PVI + LAPWI with the novel POLARx™, were compared to 40 consecutive patients who underwent the same procedure with the established Arctic Front Advance PRO™. Results Acute isolation was achieved in all PVs in both groups and left posterior wall isolation (LAPWI) was achieved in 38 patients (95%) in the POLARx group and in 36 patients (90%) in Arctic Front group. Procedural outcomes were similar between both groups, except for lower temperatures during cryoenergy in the POLARx group, for both pulmonary vein isolation (PVI) and LAPWI. Conclusion LAPWI + PVI with the novel POLARx™ Cryoballoon is feasible and safe; the results are comparable with the Arctic Front Advance PRO™ system.

In order to achieve the LAPWI, the lumen mapping catheter was placed deeply in the LSPV to stabilize the CB-A. As per our standard protocol, cryothermal lesions lasted 120 s. [5][6][7][8]14 The first cryoapplication was performed partially overlapping LSPV ostium. By a slight clockwise rotation and progressive "pullback" of the sheath while keeping the CB in contact with the posterior wall, consecutive overlapping freezes were applied along the LAPW. The same maneuver was performed from the right superior pulmonary vein (RSPV) and from inferior PVs for the inferior portion of LAPW. At the end of the procedure, in order to evaluate LAPWI pacing maneuvers to test entrance and exit block were performed. A post ablation 3D electroanatomical map (CARTO 3, Biosense Webster, USA) was performed with a multielectrode mapping catheter (Pentaray, Biosense Webster, USA). Whenever LAPWI could not be achieved using cryoablation alone, pointby-point radiofrequency ablation (SmarTouch, Biosense Webster, USA) was used. Radiofrequency was delivered in a power-controlled mode with a power limit of 30 W and with an ablation index target of 400. In case of LET ≥ 40 • C the ablation was interrupted.
During the entire procedure, activated clotting time was maintained over 300 s by supplementing heparin infusion as required.

2.3
Statistical analysis

RESULTS
Eighty patients were included in the study, the first 40 patients underwent an index PVI + LAPWI with the Arctic Front Advance PRO™ ablation system and the following 40 patients with the POLARx™. Baseline demographics and clinical data are displayed in Table 1. There was no significant difference between both cohorts, except for dyslipidemia  Table 2. The procedural outcomes are detailed in

DISCUSSION
To the best of our knowledge, this is the first study comparing PVI +   is consistent with previous reports. [10][11][12] Noticeably, the temperatures were also lower during applications on the posterior wall. The temperatures displayed on the console of both systems are commonly referred to as inner balloon temperature. The latter are the result of the return gas temperature from inside the cryoballoon, and do not reflect the values at the tissue balloon interface. The inner balloon strongly depends on independent variables such as the balloon position within the PV ostium and on the LAPW, balloon to PV diameter ratio, and balloon manipulation by the operator. As a result, inner balloon temperature may differ from balloon to balloon, despite similarities in energy delivery and overall approach. In addition, although the position of the thermocouple (measuring the internal balloon gas temperature) is similar between both systems (21.5 mm from injection coil), 12  The complication rate was low, comparable between both technologies; the lower temperatures attained during PVI and LAPWI ablation with the POLARx did not translate in higher rates of PNP or lower LET.
Finally, the current study confirms that adding LAPWI to PVI with cryoballoon technology does not increase complication rates.

LIMITATIONS
The study was a non-randomized analysis of consecutive patients conducted in a relatively limited number of patients. Furthermore, it reports a single center experience.
No esophagogastroduodenoscopy was performed after ablation, esophageal damage might have been underestimated. Finally, the lack of a clinical follow-up or remap prevent from defining any algorithms, such as a temperature-guided approach, for the new ablation system.

CONCLUSIONS
LAPWI + PVI with the novel POLARx™ Cryoballoon is feasible and safe. No differences were found compared to the traditional cryoablation platform in terms of acute efficacy and complications. Long term follow-up studies are awaited to assess the clinical outcome.