Methods
Study Population
The cohort study consisted in prospectively collecting data of the first 20 patients undergoing PVI for AF with the novel POLARx™ CB. They were compared to a historical cohort took from a study that evaluated the Arctic Front Advance PRO™ balloon (CB-4) against its previous version13. The option for choosing this particular group of controls was due to convenience and completeness of the clinical and procedural data available. In this case, the whole CB-4 group had data gathered for comparison. The project and data collection activities conform to the principles outlined in the Declaration of Helsinki, and each patient included provided informed written consent. The study was approved by the local Institutional Committee on Human Research.
Aims of the study
This study aims to evaluate the efficacy and safety of the POLARx™ CB, comparing it to the established Arctic Front Advance PRO™. The chosen primary endpoint was acute success, defined as success in electrically isolating all the four veins in the procedure. Secondary outcomes were: complications rate, procedural duration, fluoroscopy time, ablation time, time-to-isolation (TTI), lowest temperature reached, number of veins isolated with a single cryo cycle, and high-sensitive troponin I (hs-TnI) level 24 hours after the procedure.
Procedural workflow
All the procedures were performed under deep sedation. A decapolar was positioned in the coronary sinus and a quadripolar in superior vena cava (SVC). Intravenous unfractionated heparin was administered (100 UI/kg), aiming for an activated clotting time (ACT) between 350-450 seconds. Standard fluoroscopy-guided transseptal puncture was performed, and the standard SL0 sheath was changed over-the-wire for a Flexcath™ 15Fr or a POLARSHEATH™ 16Fr. The veins were ablated following the sequence: left superior pulmonary vein (LSPV), left inferior pulmonary vein (LIPV), right inferior pulmonary vein (RIPV), and right superior pulmonary vein (RSPV). The vein occlusion was checked with contrast dye injection. The freezing time duration and the number of attempts for each vein, as well as additional lesions or procedures, were left to the operator’s discretion. Usually, applications would vary from 180 to 300 sec, without bonus freeze. During ablation, vein potentials were monitored in real-time whenever possible by a circular wire-catheter (Achieve™ or POLARMAP™). When right pulmonary veins were ablated, the right phrenic nerve was paced through the SVC catheter, and diaphragmatic movements were closely monitored by upper-abdomen palpation or movement sensor in case of POLARx™, triggering immediate freezing stop in case of ceasing or weakening of diaphragmatic movements. Esophageal temperature was monitored throughout the procedure. An esophageal temperature of less than 18ºC would trigger immediate freeze cessation. After ablation, entrance block was confirmed by the absence of vein potentials, and exit block by failure in capturing the left atrium by stimulating inside the vein with maximum output. The POLARx™ console screen and gears are displayed in figure 1 . To see in detail the freezing-thawing process using the POLARx™ system, together with the built-in diaphragm movement sensor, watch the video 1 in supplementary material. Twenty four hours after ablation all patients had hs-TnI levels measured.
Statistical analysis
Continuous variables were evaluated for normality using the Shapiro-Wilk test. Due to their non-normal distribution, they were described as median (Q1-Q3). Mann-Whitney U test was used for comparisons between them. Categorical variables were expressed as number (%) and were analyzed using the Chi²-test or Fisher’s exact test. Since this is an exploratory study, with no equal previous study, no sample size calculation was performed. Statistical tests were based on a two-sided significance level of 0.05. SPSS statistical software v.23.0 (IBM, Armonk, NY, USA) was used for all statistical analyzes.