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.