PED

The vascular intervention world has been buzzing with exciting news as of late. EV3 recently purchased Chestnut Medical Technologies and is now beginning to offer their products to the cerebral angiography community.



One of the most exciting new products that's out there is the Pipeline Embolization Device (PED) which was developed by Chestnut. The PED is a v. flexible, microcatheter-delivered, self-expanding endovascular "stent-like" construct used for the occlusion of cerebral aneurysms. It is created from microfilaments of platinum and cobalt chromium which are braided to form a mesh cylinder. The device is delivered so that it expands to oppose the walls of the parent vessel from which the aneurysm arises, and acts to completely occlude the aneurysm from receiving circulation while simultaneously encouraging reconstruction and normalization of cerebral vasculature in the affected area.

One of the papers I read delivered a fantastic history detailing the history of aneurysm treatment. In 1992, Boston Scientific/Target created the Guglielmi detachable coil system which opened up the world to treatment of aneurysms with metal coils. 10 years later, Boston Scientific introduced the Neuroform stent, specifically used as an adjunct to coil embolization. That being said, the best evidence practice for the last couple of years has been to coil and stent.

The problem with this method is that it fails dramatically for aneurysms that are not narrow-necked, berry-shaped and small. Not everyone is blessed enough to have only a tiny aneurysm, and there's many a time in clinic where I've been witness to gigantic aneurysms - you really wonder how these people live. When you look at the statistics, 38.3% find complete occlusion at the 12 month follow-up. Another study found a 19% rate of complete occlusion at 18 months. While the rates are much better for small aneurysms (66%), there are still a rather large percentage of those not receiving a clean bill of health. These include those with small aneurysms, and most dramatically, those with large, giant, wide-necked and non-saccular (fusiform) aneurysms.

So let's examine why. When examining the coiling, we note that with maximal packing, the majority of the volume within coiled aneurysms does NOT get filled with embolic material (70-80%). This allows for blood flow to continue into the aneurysm. It is also dangerous to breach the sac of the aneurysm in the first place, so avoidance of aneurysm entry would be optimal. When considering adjunctive stent placement, many stents provide inadequate metal area coverage when deployed. The Neuroform stent itself provides only 6.5-9.5% metal coverage, and so cannot act as a stand-alone therapy.

In comes Chestnut/EV3 with the PED. The PED provides 30-35% metal coverage at maximal expansion, which is obviously much higher coverage. It is deployed just proximal to the neck of the aneurysm in the parent vessel, and thus does not require entry to the aneurysm sac, effectively circumventing accidental perforation. The deployment provides sufficient coverage to physiologically exclude the lesion from circulation, yet is porous enough to preserve the patency of branch vessels covered by the construct. The really cool thing about it is that not only does it effectively occlude aneurysm blood flow (>90% reach full occlusion by the 6-month followup), it facilitates the growth of normal vasculature in the region - "the stent implantation may change the configuration of the parent vessel, changing the anatomy of the parent vessel-aneurysm complex and the aneurysm inflow zone...implantation of the stent within the affected vessel ideally acts as a stimulus and provides a scaffolding to support neointimal overgrowth across the aneurysm neck defect, thereby facilitating the biological remodeling of the deficient segment of the parent artery".




One of the most incredible things is that the PED can act as a stand-alone therapy (15/17 aneurysms in rabbits achieved complete occlusion with only one PED deployed). This may represent a paradigm shift from coiling to stand-alone stenting in the future. From an economical perspective, it will be much cheaper to perform this, both on the basis of materials required (one-three stents vs. ten coils +/- adjunctive stents) and on radiologist time spent in procedure.

With all new products, there are obviously limitations. Placement of the PED precludes future coiling because it blocks neck access, therefore the suggestion has been to jail a microcatheter in the event that re-entry is required. There is also no clear evidence to show how PED affect bifurcation aneurysms, and if occlusion of one side will increase flow to the next one. Lastly, there is dual antiplatelet therapy required during the procedure (aspirin and clopidogrel), which is obviously contraindicated for the context of acute subarachnoid hemorrhage.

Nonetheless, the PED invites a new way to look at cerebral vasculature intervention, and shows that even today companies are still paving the way towards new technologies to aid those afflicted by disease. I think the most exciting thing is that this is no band-aid solution - the PED acts not only to cut off blood flow to the aneurysm, but it also encourages the growth of appropriate vasculature through its scaffolding. HOW FREAKING COOL.

You can read the original papers by clicking on the titles of the papers below:

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Lylyk, P., Miranda, C., Ceratto, R., Ferrario, A., Scrivano, E., Luna, H. R., et al. (2009) Curative Endovascular Reconstruction of Cerebral Aneurysms with the Pipeline Embolization Device: The Buenos Aires Experience. Neurosurgery, 64(4), 632-643.

Fiorella, D., Woo, H. H., Albuquerque, F. C., & Nelson, P. K. (2008). Definitive Reconstruction of Circumferential, Fusiform Intracranial Aneurysms with the Pipeline Embolization Device. Neurosurgery, 62(5), 1115-1121.