Flow diverting, stenting and beyond—HPC technology offers “limitless” potential in neurointervention


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Victoria Hellstern

Following the publication of a study assessing the use of Hydrophilic Polymer Coating (HPC) technology with the p64 MW flow modulation device (phenox) at her centre earlier this year, Victoria Hellstern (Klinikum Stuttgart, Stuttgart, Germany) discusses the significance held by this unique surface modification product in the neurointervention space—and offers her thoughts on further avenues it could move into in the future.

What is the unmet need that the HPC technology could resolve for physicians and their patients?

The introduction of flow diverters to the neurointervention field about 10–12 years ago changed treatment options for intracranial aneurysms dramatically. Formerly untreatable aneurysms have become treatable and, for other aneurysms, the treatment has become much easier. However, one of the major drawbacks for flow diverter implantation has always been the need for dual antiplatelet therapy (DAPT), as this increases the risks for a range of ischaemic and haemorrhagic complications. There are also compliance problems, as the patient needs to take two medications daily rather than just one, as well as the fact that patients who are on DAPT are more likely to experience bleeding complications if they undergo further surgeries in the future.

These are the exact issues that phenox’s HPC-coated p64 MW device is seeking to address—as the only commercially available flow diverter with instructions for use (IFU) explicitly stating that it should be used alongside single antiplatelet therapy (SAPT) right now. With other surface-modified flow diverters, the decision to use SAPT can be made if appropriate in a given situation, but their IFU will still recommend DAPT, whereas we can use the coated p64 MW with SAPT in routine clinical practice.

Please could you outline the design, objectives and findings from your recent study published in CardioVascular and Interventional Radiology?

In the paper, we summarised our daily clinical experiences with the HPC-coated version of the p64 MW flow diverter.1 It reports a retrospective, single-centre study of 102 patients with 132 aneurysms, which is a very large cohort in the neurointervention field, from March 2020 to December 2021. All patients underwent treatment of their unruptured, anterior-circulation, saccular aneurysms with the p64 MW device and SAPT (prasugrel). We compared safety and effectiveness outcomes in our study against another paper published by our group2, involving the uncoated p64 MW device with DAPT, as well as other historical flow diversion literature.

After analysing periprocedural and postprocedural complication rates, we concluded that flow diversion with SAPT has a solid safety profile—for example, our periprocedural complications were mostly technical and had no clinical consequences for the patients. It is also really important to highlight the fact we had no ischaemic or haemorrhagic complications at all during the procedures, even though they were performed under SAPT. We performed magnetic resonance imaging (MRI) too, using diffusion-weighted imaging (DWI) lesions as safety markers of flow diverter implantation, and basically found that three quarters of the patients had zero or very minimal pathological signals. These data indicate that p64 implantation with prasugrel is at least as safe as uncoated flow diverter implantation with DAPT.

We also looked at short- and mid-term occlusion rates, and overall efficacy of these treatments, and these were pretty impressive as well. We observed occlusion rates of 70% at up to three months, and nearly 85% after nine months. In some locations, such as internal carotid artery (ICA) aneurysms, we had even higher occlusion rates at 73% and 88%, respectively. These rates are exceedingly high. As such, we feel that the coated p64 MW with a SAPT strategy results in faster and higher aneurysm occlusion rates. The ongoing COATING trial, led by Laurent Pierot (University Hospital of Reims, Reims, France), is also currently investigating this—and we hope and expect that they will confirm our findings, and raise the bar in surface modification in the process.

Why does this study provide particularly positive and durable evidence that coating works in flow diversion?

It is the first study that has been done in elective cases with such a high number of patients. A lot of other studies have involved acute subarachnoid haemorrhage (SAH) patients with really small numbers, whereas we used elective patients throughout our daily clinical practice. The biggest advantage of this technology will probably be seen in those acute SAHs, because it will change treatment options for those patients dramatically, but we were able to show that an even wider group of less urgent aneurysm cases could also benefit from reduced thromboembolic complications with a coated flow diverter plus SAPT.

Phenox is now in the process of launching its HPC technology for stent-assisted coiling too—why is this a significant development?

The benefits offered by surface modification in stent-assisted coiling are similar to those outlined previously in flow diverter devices, in terms of removing the need for DAPT and, in turn, reducing ischaemic and haemorrhagic complications. However, the antithrombotic coating of an open-cell stent like the pEGASUS HPC device (phenox) is something we have never had before in neurointervention. And, in the future, it could even be deployed in the treatment of stroke or intracranial stenosis as well as aneurysms, so I think the use indications will continue to spread even more widely and more rapidly.

p64 MW HPC flow diverter and pEGASUS HPC stent

The application of flow diverters in middle cerebral artery (MCA) bifurcation aneurysms remains highly controversial in the field, and many operators prefer to stick with stent-assisted coiling rather than flow diversion. I think phenox’s coated stent will meet the needs of those people, and allow them to also use SAPT in the future, increasing the safety profile of the procedure as well as simplifying patient care afterwards. The most beneficial cases will probably be those bifurcation aneurysms, and posterior-circulation aneurysms, because they are associated with higher rates of ischaemic complications when treated with a flow diverter. These cases now stand to benefit from reduced complications with stent-assisted coiling and SAPT as well.

Is it likely the coating will be just as successful in safely reducing the need for DAPT once it moves to stents, and are there any key differences compared to flow diverters?

I think we have proved that the HPC technology works really well with the p64 MW, and—compared to the pEGASUS HPC stent—uncoated flow diverter devices have a much higher thrombogenicity, because they have a lot of wires and the device has a far greater surface area. So, if the coating is strong enough to allow implantation of a flow diverter alongside SAPT, it would make sense for it to easily enable implantation of pEGASUS HPC with SAPT. I would not expect there to be any problems; if anything, coating the p64 MW was the trickier part, and shifting to stent-assisted coiling is even more likely to be successful. You can also start to think about implanting these devices with aspirin only. We do not have the data to back this up yet, but it is a possibility that would work—and that would be extremely beneficial, because aspirin is so easy to use and safe.

Finally, how would you assess the potential offered by this coating technology—in neurointervention, but also in other spaces as well?

I think the most essential benefit in neurointervention will be that it allows us to really change and simplify our management protocols for the patient. I also told one of my colleagues in cardiology about this coating recently, and he said he would love to have that in his practice—because they have many of the same DAPT-related problems with coronary stents. The feedback from the trauma surgeons in our centre is great as well. They are really happy with the coated flow diverters, as they can operate under SAPT with fewer worries. You could also begin to think about coating microcatheters or guidewires—in fact, pretty much anything we use in neurointervention—to reduce the risk of thromboembolic complications. Really, I think that the future applications in our space could be limitless.



  1. Hellstern, V; Aguilar Pérez, M; Henkes, E et al. Use of a p64 MW Flow Diverter with Hydrophilic Polymer Coating (HPC) and Prasugrel Single Antiplatelet Therapy for the Treatment of Unruptured Anterior Circulation Aneurysms: Safety Data and Short-term Occlusion Rates. Cardiovasc Intervent Radiol. 2022; 45: 1364–74.
  2. Aguilar Pérez, M; Henkes, E; Hellstern, V et al. Endovascular Treatment of Anterior Circulation Aneurysms With the p64 Flow Modulation Device: Mid- and Long-Term Results in 617 Aneurysms From a Single Center. Operative Neurosurgery. 2021; 20(4): 355–63.


Victoria Hellstern is a leading consultant for Interventional Neuroradiology in the Department of Diagnostic and Interventional Neuroradiology at Klinikum Stuttgart in Stuttgart, Germany. She also holds the European Diploma in Neuroradiology (EDiNR), and her research interests include surface-modified flow diverters.


DISCLAIMER: The p64 MW (HPC) Flow Modulation Device and pEGASUS (HPC) Stent System have received the CE Mark. They are not approved for sale nor are they available for sale or use in the United States.


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