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New clinical data from the COATING randomised controlled trial (RCT)—presented for the first time at the 2026 LINNC Paris course (1–3 June, Paris, France)—are likely to further bolster the neurointerventional community’s confidence in Hydrophilic Polymer Coating (HPC; WallabyPhenox) surface modification as a potential means for safely reducing their patients’ antiplatelet therapy burden following intracranial aneurysm procedures. That is according to Laurent Pierot (Reims University Hospitals, Reims, France) and Omer Eker (Bordeaux University Hospital, Bordeaux, France), who spoke to NeuroNews to offer fresh perspectives on the trial’s latest findings.
“For a very long time, the main problem we’ve had to manage during the endovascular treatment of intracranial aneurysms with stents or flow diverters has been thromboembolic complications—which occur at a rate of around 10%,” Pierot avers. “That’s why, by using surface modification, we are trying to reduce platelet aggregation when we place a device inside the artery.”
The COATING study—a prospective RCT for which Pierot is the principal investigator—was devised to evaluate one such surface modification technology: HPC. In the trial, 171 unruptured aneurysm patients were enrolled across 15 European centres, and randomised to treatment with either the p64 MW HPC flow-modulation device plus single antiplatelet therapy (SAPT) or the uncoated version of the p64 MW device plus dual antiplatelet therapy (DAPT).
According to Pierot, the trial utilised a novel yet conservative primary endpoint—core lab-adjudicated diffusion-weighted imaging (DWI) lesions observed within 48 hours of the index procedure—that allowed investigators to compare thromboembolic events between the study arms in a “relatively objective” way while also reducing the number of patients required to achieve sufficient statistical power. Pierot notes that, in the years since the trial was first introduced, many other published papers have examined DWI lesions as an endpoint of interest—with COATING investigator Eker adding that “it has become a new standard”, with its only tangible limitation being the fact that it captures thromboembolic events relating to the entire procedure as opposed to the implanted device alone.
“DWI is the most sensitive way to assess any thromboembolic event,” he explains. “In our practice, anywhere from 30–60% of procedures are associated with these events—most of which are asymptomatic. So, comparing DWI lesions—rather than three-month clinical outcomes—is the best way to ensure we don’t miss any thromboembolic events. Secondly, if we had used a clinical primary endpoint, we would’ve needed hundreds or even thousands of patients in each study arm, which is not feasible given the numbers of aneurysm patients who stand to benefit from flow diversion.”
Analyses of this primary endpoint were presented by Pierot at last year’s LINNC Paris meeting, successfully demonstrating non-inferiority with HPC plus SAPT versus no HPC plus DAPT, as per mean numbers of DWI lesions of six and 5.3, respectively. Additionally, one-month safety data showed no statistically significant difference in thromboembolic events between the two groups. These findings were subsequently published in the Journal of NeuroInterventional Surgery.
And, now, these initial positive data have been backed up by analyses of COATING’s longer-term results—including, in Pierot’s view, the “important” step of evaluating rates of delayed thromboembolic complications, haemorrhagic events, and in-stent stenosis, as well as aneurysm occlusion outcomes at six and 12 months.
Ultimately, the between-group parity in thromboembolic events observed at one month was maintained out to one year, while morbimortality rates—assessed via modified Rankin scale (mRS) scores—were also statistically similar with HPC versus without at both 30 days and 12 months post-procedure. Pierot goes on to note that there were no statistically significant differences between the study groups in terms of intra-procedural or post-procedural cerebral haemorrhagic events out to one year.
“I have travelled all over the world to present on the COATING trial, and I can tell you that a lot of physicians want a simple, logical protocol that can be applied to every single case”
Laurent Pierot
Regarding its key efficacy endpoints, the trial found a statistically non-significant trend towards improved complete aneurysm occlusion at six months in the HPC group (74.4%) versus the non-HPC group (63.5%)—although these rates levelled out to 79.5% and 76.8%, respectively, at 12 months.
“This is probably because being under DAPT slows down the process of intra-aneurysmal thrombosis, meaning patients receiving SAPT obtain complete occlusion more rapidly,” Pierot says. “But, at one year, everything is more or less the same in both groups.”
Pierot also highlights the “very interesting” finding that, among patients with available digital subtraction angiography (DSA) data, in-stent stenosis rates were statistically similar between the HPC and non-HPC groups at both six months (30.2% vs 24.1%) and 12 months (15.2% vs 15.7%) as well. Additionally, zero target aneurysm retreatments were required at six and 12 months with HPC, while one retreatment—caused by a technical problem as opposed to aneurysm recurrence—was needed out to 12 months without HPC.
“This is very relevant to clinical practice,” Eker states, commenting on the significance of these data. “Thromboembolic complications and aneurysm occlusion outcomes are multifactorial. Our goal as physicians is to give patients the best chance of achieving complete occlusion while minimising complications, and, if we can remove one of the factors that contributes to these complications—for example, the haemorrhagic risks associated with DAPT, especially in older patients—this will be beneficial.
“The data also suggest that aneurysm thrombosis occurred more quickly in the HPC group, offering hope for us to consider reducing the duration of antiplatelet therapy in cases where the aneurysm has occluded completely at an earlier stage. This is also of benefit to the patient, as they could undergo antiplatelet therapy for six or eight months, rather than 12, decreasing their exposure to the complications associated with these therapies.”
In addition to reducing the haemorrhagic risks associated with prolonged DAPT intake, Pierot is keen to point out that reverting to SAPT lowers a patient’s daily medication burden—which could involve, for example, ticagrelor in the morning and evening, and aspirin in the middle of the day—meaning they are more likely to adhere to their prescribed drug regimen post-treatment, further reducing the likelihood of longer-term complications.
“Based on this study, we can confidently say that, with SAPT—provided you have the HPC surface modification—patients will do as well as they would with DAPT alongside a bare flow diverter,” Eker opines. “This is a significant improvement in our practice.”
At this stage, some of the most experienced neurointerventionists have already been utilising surface-modified flow diverters plus SAPT in real-world practice for several years. However, Pierot feels that these results provide the scientific evidence that is needed to ensure this approach can be adopted more widely, in addition to establishing HPC as the only surface modification technology supported by randomised trial data for use alongside SAPT—a consideration that may apply to other stents and even intrasaccular devices as well as flow diverters.
“I have travelled all over the world to present on the COATING trial, and I can tell you that a lot of physicians want a simple, logical protocol that can be applied to every single case,” he adds.
“Flow diversion is a fantastic technique, and it allows us to treat many complex aneurysms that we couldn’t tackle before,” Eker concludes. “However, simplification is required for this technique to become more widespread—and simplification of the antiplatelet therapy is mandatory. As such, COATING is a significant milestone in the democratisation of flow diversion.”
Pierot and Eker are ultimately in agreement that, based on these data, HPC stands as the first and only surface modification with proven safety and efficacy when deployed alongside SAPT in neurovascular procedures.
