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.