Discussion
To the best of your knowledge, this is the first clinical study
comparing the novel POLARx™ CB to the already established Arctic Front
Advance PRO™.
Briefly, we found that the POLARx™ CB had a similar profile in terms of
efficacy and safety when compared to the Medtronic’s CB. Despite
achieving all veins isolation by the end of the procedure in 100% of
the patients, the POLARx™ CB demanded a higher procedural time and had a
lower number of veins isolated in the first attempt. Interestingly, the
cryoenergy application time was the same. A possible explanation for
that could be the lack of experience with some of the new features and
workflow of the POLARx™, an issue intrinsic to the first procedures with
new devices. Notwithstanding the similarities between tools and
procedural workflow, some differences in the practical handling were
consensus between our operators. The POLARSHEATH™ introducer, although
1Fr larger, tended to cross the septum more easily and smoothly due to
its more gradual taper from the dilator to the sheath. We also had the
feeling that the set sheath plus balloon was softer and more flexible
when compared to the Flexcath™ plus CB. This can be seen as an advantage
since it allows easier vein cannulation, or disadvantage once it can
make more difficult to reach vein occlusion. Another point against the
novel CB is the impossibility to perform the pull-down maneuver. This is
due to a build-in sensor of balloon dislodgement aiming to enhance
procedural safety. When the CB is pulled to seal the inferior vein
segment, the system often detects it as an involuntary CB displacement
and it stops the cryoenergy delivery immediately, hindering a maneuver
commonly used to seal the vein.
An interesting finding is the difference found in the minimum
temperature reached. The median lowest temperature and temperature
reached when the vein turned isolated was approximately 10ºC lower in
the POLARx™ group. Despite that, the TTI was similar between groups, and
so does the troponin level. These findings point to a non-different
tissue damage, making us theorize that the temperature inside the atrial
tissue does not differ between groups, and that this temperature
difference may be due to a different way or location where it is
measured. Since we did not perform routinely pre or post voltage map, we
were not able to evaluate acute and/or chronic scar extension. In one of
the POLARx™ patients, we performed successfully, besides PVI, posterior
wall isolation exclusively using the CB; the result can be seen in a
previous publication12.
No complication was observed in the 20 POLARx™ cases, and 4 minor
complications were observed in the Arctic Advance PRO™ group: 3
temporary phrenic nerve palsies and a pericardial effusion without
hemodynamic compromise. Since, fortunately, as in other AF cryoablation
cohorts, our complication incidence was low, we could not draw
significant conclusions about group differences. Another interesting
feature of POLARx™ is the possibility to monitor diaphragm contraction
with the diaphragmatic movement sensor (DMS), a sensor that shows it in
real-time as a quantified number in percentage. If even a reduction in
diaphragm contraction is detected it triggers a red warning sign,
allowing earlier cryoenergy delivery stop. Unfortunately, it is not
always possible to use the DMS together with hand palpation, since the
pressure applied by the hand cause error in the DMS reading, as can be
seen in video 1 (supplementary material). The summary of pros
and cons of both technologies is available in figure 3 .
Owing to the fact that POLARx™ has just entered the market in Europe, no
data from previous studies is available to be compared with ours. But,
taking into account previous studies comparing different CB generations,
we observe that evolution is possible and desired. Since the release of
the first generation (CB-1), Medtronic improved the design 3 times,
being born: Arctic Front Advance™ (CB-2), Arctic Front Advance ST™
(CB-3), and lastly, the Arctic Front Advance PRO™ (CB-4). A real-world
study evaluating 480 patients, 120 in each generation group, found a
progressive reduction in procedural duration (150 min, 95 min, 90 min,
75 min, from CB-1 to CB-4, as well as a reduction in fluoroscopy time
and ablation duration, with the same success rate. This denotes that
even if reaching a higher success was not possible, the evolution in
balloon architecture improved the handling, making the procedure
easier11.
Summarizing, our study found that the novel POLARx™ CB had similar
efficacy and safety compared to the Arctic Front Advance PRO™ CB. It
also achieved lower temperatures, but with similar TTIs. However, it was
associated with a longer procedure and a lower number of pulmonary veins
isolated in the first attempt. The DMS for phrenic monitoring is useful
and has the potential to make the procedure safer.