Multiple pieces of clinical research supporting the use of flow diverter devices to treat intracranial aneurysms have come to light so far in 2021. In the past few weeks alone, data from a multicentre pivotal trial assessing the Flow redirection endoluminal device (FRED; MicroVention/Terumo) stent system have been published in the Journal of NeuroInterventional Surgery (JNIS), while five-year results from the SCENT (Surpass intracranial aneurysm embolisation system pivotal trial to treat large or giant wide-neck aneurysms; Stryker Neurovascular) study were presented at the Society of NeuroInterventional Surgery’s 18th annual meeting (SNIS; 26–29 July 2021, Colorado Springs, USA and virtual).
The growing body of evidence in favour of using flow diversion technologies for this indication—and the emergence of several different devices in this space in recent times—is a “welcome and exciting development”, according to Philip M Meyers of the Neurointervention Clinic at St Luke’s Health System in Boise, USA, who is also past president of SNIS and editor-in-chief of NeuroNews. “There have been numerous important publications in the neurointerventional space over the past year,” he adds. “Tremendous growth in applications of new techniques and devices requires ongoing technology assessment and comparative effectiveness analysis. The good news is that patients have many options. Physicians and surgeons must help patients select the best strategies to address their unique situations based on best medical and scientific evidence.”
The use of flow diverter devices to treat intracranial aneurysms dates back roughly a full decade to the US Food and Drug Administration (FDA) granting Covidien premarket approval for its Pipeline embolisation device (PED) in 2011—a company and, therefore, a technology, that has since been acquired by Medtronic. This has made Medtronic and the PED frontrunners in the field, and fresh evidence on this device is still emerging 10 years on, with data on 1,000 aneurysms from a single-centre registry, published in Neurosurgery in June 2021, concluding that it is safe and effective at up to 13 years of follow-up.
And, even in the short window of time since these results were published, key data on other flow diverter products have been presented to the neurointervention world. This year’s SNIS annual meeting saw Alexander L Coon (director of Cerebrovascular & Endovascular Neurosurgery, Carondelet Neurological Institute, St Joseph’s Hospital, Tucson, USA) present five-year results from the SCENT trial of the Surpass Streamline device—the largest prospective flow diversion study in this space to date, he claimed.
This trial, which was set up to evaluate the safety and effectiveness of Stryker’s device for the endovascular treatment of patients with unruptured large or giant intracranial aneurysms of the internal carotid artery (ICA) to the ICA terminus, involved 180 patients from 26 centres in the USA. Coon noted in his late-breaking abstract presentation that the SCENT trial met its primary safety and efficacy endpoints at 12 months, and these data were used to support FDA investigational device exemption (IDE) premarket approval of the Surpass Streamline flow diverter in 2018.
Moving on to discuss the five-year safety outcomes from the trial, Coon stated that the number of neurological deaths did not increase from 12 months through 60 months—with one new case being reported after 60 months—before adding that there were just three cases of new or worsening major ipsilateral stroke from 12 months through 60 months, and no additional late aneurysm ruptures over this period. Regarding five-year angiographic effectiveness, he reported a 90.2% rate of complete aneurysm occlusion, a 1.4% rate of implant stenosis (≥50%) and a 2.9% rate of parent artery stenosis (≥50%) at 60 months, in addition to a “very low” incidence of aneurysm retreatment (2.8%, n=5), and an 80.7% frequency of patients reporting unchanged or improved functional outcome scores compared to baseline.
He concluded that the long-term secondary safety and effectiveness results demonstrated consistency with 12-month primary safety and effectiveness results from the SCENT trial, asserting that “these findings reinforce the benefit of minimising the risk of aneurysm rupture following treatment of aneurysms greater than or equal to 10mm in size with the Surpass Streamline flow diverter—supported by high occlusion rates and low rates of delayed adverse events”.
Discussing the wider implications of these findings, Meyers says: “Long-term evidence is very important, because many devices and their applications in neurointervention are relatively new. Short-term data demonstrate safety and efficacy but, for diseases with lifetime risk, longer term information helps to answer important questions for patients and caregivers alike.”
The other piece of major evidence on flow diversion technology seen recently—results from the US pivotal trial of FRED system—has been published in JNIS by Cameron G McDougall (director of Endovascular Neurosurgery, Johns Hopkins Hospital, Baltimore, USA) et al. “Although the FRED system is a relative newcomer to the flow diversion field, a growing body of high-quality evidence consistently shows it provides satisfactory safety and efficacy results,” the authors note in their report.
In this multicentre, prospective, single-arm, IDE clinical study, a total of 145 patients with aneurysms of unfavourable morphology for traditional endovascular therapies— including large, wide-necked and fusiform aneurysms—were enrolled across 23 centres, and underwent attempted placement of the FRED stent system. After one year of follow-up, nine patients (6.2%) met the composite primary safety endpoint of major stroke or death within 30 days, or major ipsilateral stroke or neurological death after 30 days. Further, regarding effectiveness, 80 of 139 patients (57.6%) with angiograms interpretable at follow-up met the criteria for primary effectiveness—that being complete aneurysm occlusion without stenosis >50%, and no retreatment.
McDougall et al conclude, therefore, that the FRED system is safe and effective for the treatment of intracranial aneurysms—and note that, on this basis, it was granted premarket approval by the FDA in January 2020. They also highlight that “very low” rates of disabling stroke or death seen here are “reassuring”, as they have been consistently reflected in other trials of the device. This trial and others involving the FRED system have reported “improving rates of complete aneurysm occlusion over time”, they add—a trend also observed in studies of PED.
Recently, French medical technology firm Balt has emerged as the newest key player in the flow diversion sphere. Having received a CE mark in mid-2020, its Silk Vista device has been the subject of two academic papers this year—one in JNIS detailing the first multicentre experience using it in intracranial aneurysms, and another outlining safety outcomes in a short-term, observational study, which was published in Frontiers in Neurology. While this newer innovation is yet to obtain the same bulk of clinical evidence as PED and Surpass, Meyers believes even these early findings contribute to the growing positivity surrounding flow diversion techniques right now.
“Proliferation in new neurointervention technologies is a welcome and exciting development,” Meyers states. “The pace of innovation is accelerating, which should lead to progress including better, safer, more effective and more efficient devices. However, with that comes the responsibility to define the most appropriate indications and applications for each. This makes critical reasoning and data collection even more important. The number of patients with certain cerebrovascular diseases is limited— and we must work collectively to maximise the cultivation of useful knowledge.
“Advancement in flow diversion technologies is already underway,” he continues. “Bioactive coatings, improved designs, and even absorbable or temporary devices, are being developed. Our industry partners are very good at shepherding this process forward. If we can unlock the biological mechanisms of aneurysm formation and rupture, new medical and non-surgical treatments may evolve.”