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|NI FEATURE: THE EDITORIAL DEBATE V-- PROS AND CONS
|Year : 2019 | Volume
| Issue : 3 | Page : 665-666
Flow diverters: Hope and hype
Paritosh Pandey, Ullas V Acharya
Department of Neurosurgery and Neurovascular Intervention, Manipal Hospital, Old Airport Road, Bangalore, Karnataka, India
|Date of Web Publication||23-Jul-2019|
Dr. Paritosh Pandey
Department of Neurosurgery and Neurovascular Intervention, Manipal Hospital, Old Airport Road, Bangalore, Karnataka
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Pandey P, Acharya UV. Flow diverters: Hope and hype. Neurol India 2019;67:665-6
Flow diversion is a revolutionary concept in endovascular neuro-intervention. Previously untreatable aneurysms are now being routinely treated with these devices. In a matter of few years, this technique has attained massive popularity in terms of its utility and usage. In that sense, it is surprising that there are very few reports of flow diversion emanating from India, though India tends to have potential cases with an aneurysm within its population, who are appropriate for flow diverter treatment. This is despite the fact that there are multiple centers offering this treatment across the country.,, In this context, we read the study on the experience with flow-diverters being published in this issue of Neurology India with great interest, as it records important details pertaining to the usage and clinical efficacy of flow diverter treatment in complex aneurysms with a meticulous follow up of the cases.
Significant evolution in the last two to three decades in the design and construct of intracranial stents to maintain the ideal balance between porosity and metal coverage has led to the flow diverting effect with reconstruction of the vessel; as well as the exclusion of the aneurysm from the parent vessel circulation. Braided designs of a new generation, intraluminal support devices with a metal ratio of 18-22% in stents like the Leo (Balt) and LVIS (MicroVention), confer possible flow diverting properties. In some studies, where patients with a complex aneurysm morphology involving the distal anterior circulation or the vertebrobasilar system were included, the effects similar to flow diverters either used alone or in overlapping/telescoping fashion were shown., However, a porosity of around 50-70% is reported to be the ideal standard for maintaining the flow diverting effect and aneurysmal occlusion.
The filament size is important as it can be related to the intra-aneurysmal circulation and side-branch arterial patency. The success of flow diversion in the treatment of cerebral aneurysms has expanded the armamentarium of flow diverters beyond the archetypical pipeline embolization device (PED; Medtronic) and flow re-direction endoluminal device (FRED; Microvention), discussed in the present study. The currently available spectrum of flow diverters also include Silk (Balt), Surpass (Stryker), p64 (Phenox), Derivo (Acandis) and Cerenovus Bravo (Johnson and Johnson). Also, there are a few indigenous flow diverters from China and South Korea, named the Tubridge tubridge and FloWise, respectively.,
In the present study, flow diverters have been used mainly for large, giant and recurrent aneurysms; however, now-a-days, flow diversion is being more broadly applied to dissecting aneurysms, blister aneurysms, ruptured aneurysms and posterior circulation aneurysms. Results of the prospective study on embolization of intracranial aneurysms with the pipeline™ device (PREMIER) trial study now widens the PED use in wide-necked, small and medium intracranial aneurysms measuring ≤12 mm located in the internal carotid artery [ICA] (up to the terminus) and the proximal vertebral artery segment up to and including the posterior inferior cerebellar artery. With ongoing developments and technical advances, it is now possible to deploy FDs into smaller arteries via smaller delivery microcatheters, expanding the treatment options to small aneurysms along the distal anterior cerebral artery (ACA) and the middle cerebral artery (MCA) branches. ,
Little research has been performed to evaluate the safety and effectiveness profiles of different flow diverter devices in a head-to-head manner. Though the number of included cases in the present series is less, the authors have shared their personal experiences regarding the basic technical nuances faced during the selection of patients, as well as the tracking and deployment of these devices in-situ. A propensity score-matched cohort study comparing the PED with the FRED for internal carotid artery aneurysms revealed a comparable angiographic complete occlusion rate as well as a similar complication rate, with a possible advantage of the FRED over the PED in terms of near-complete aneurysmal obliteration. The design of the FRED differs from the PED in certain aspects. It is a paired, integrated, dual-layered (stent-within-a-stent) self-expanding braided design. The inner part of the 48 braided wires determines the working length of a FD, like PED. The outer part, which determines the total length, has 16 wires, serving as a scaffold for the inner stent. The outer stent is 3 mm longer than the inner flow diverter mesh at each end. Like Pipeline Flex, this flow diverter can be re-sheathed.
In the present study, no adjunctive coiling had been performed with FD placement. A multivariate analysis study showed adjunctive coiling to be the only technique that predicts the aneurysmal occlusion after flow diversion. In another study, complete or near-complete occlusion, as determined by a 6-month old digital subtraction angiogram (DSA), was seen in 81% of FRED-only cases, and in 95% of those with adjunctive coiling.,
Angiographic occlusion rates of the present study are in concordance with the earlier meta-analysis reports that show a continued trend of occlusion in the follow up scans. The meta-analysis study reported a 3% incidence of post-procedural subarachnoid hemorrhage (SAH) and intraparenchymal hemorrhage; however, the present study had only one major intraparenchymal bleed, possibly due to lesser number of treated aneurysms, as compared to most of the studies included in the meta-analysis. It has been established that clopidogrel non-responders have a higher rate of thrombotic complications after PED placement. It is commendable that in the present study, no thromboembolic complications were noted. This is in most likelihood related to the rigorous adherence to the protocol of performing platelet function tests in all the patients considered for FD. The meta-analysis revealed an overall thromboembolic risk of approximately 6% in a cohort of around 1451 patients. The authors have considered an aggressive and a potent antiplatelet drug, such as prasugrel, when the response was inadequate. Others have also used ticagrelor or ticlopidine as a second-choice agent, but none of these medications have been demonstrated to be measurably superior. In the present study, the dual antiplatelet therapy was continued for at least a year, and aspirin was, thereafter, administered lifelong, if the stent remained patent and features of in-stent stenosis were absent. The other common practice included the stoppage of clopidogrel after performing digital subtraction angiography 6 months postembolization, as it has been believed to contribute significantly to the improved occlusion rates seen at the 12 month postembolization evaluation.
The time is right for studies such as this one, due to the paucity of published data regarding the use of FD from this part of the world. This study would form the framework for further studies on the feasibility, as well as immediate and long-term outcomes of FD treatment for various intracranial aneurysms, including its extended off-label usage.
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