Porcine Brachial Artery Tortuosity for In Vivo Evaluation of Neuroendovascular Devices

Discussion

Forceful catheterization of the carotid siphon can result in thrombosis and vasospasm as a result of endothelial injury. The growing availability of endovascular devices for delivery to the intracranial space creates the need for a more realistic approximation of the tortuosity of the human intracranial vessels. The model described provides a robust environment to challenge the delivery and deployment of neuroendovascular devices.

Although some physical properties of microcatheters and guidewires like radio-opacity and handling can be evaluated in in vitro models, other parameters like steerability/torquability, lubricity, stiffness, and durability are better analyzed in an in vivo environment. Also, the ability to evaluate the consequences of endovascular manipulation like vessel straightening and displacement, vessel vasospasm, endothelial injury, secondary platelet adhesion, fibrin polymerization, and vessel perforation makes in vivo assessment indispensible.

Models simulating the carotid tortuosity have previously been described. Some researchers have described complex vascular surgical maneuvers like encasement of the canine CCA in carotid siphon replicas.^2,3 Also methods for generating tortuosity have been described by surgical interposition of the Dacron vascular graft (E.I. du Pont de Nemours and Company, Wilmington, Delaware) between the common trunk and the CCA, creating a vascular redundancy, which can be positioned and sutured in place to create tortuosity simulating the siphon.⁴ These vascular procedures are considerably challenging technically, requiring a skilled surgical team and a recovery period before device testing. Animal models with siphon anatomy resembling humans exist in the nonhuman primates; however, ethical and financial considerations preclude their use for endovascular device testing.⁵

Our model allows a rigorous testing of endovascular devices in a challenging tortuous vascular environment, in a model that is easily reproducible and technically much less challenging. Device performance can be evaluated on the basis of both the qualitative experience of the device while negotiating the tortuous vasculature and the angiographic response secondary to navigation. The technique for inducing the tortuosity is very feasible and reproducible and requires no prior surgical preparation. We have successfully used this vascular territory to evaluate commercially available versions of guidewires, microcatheters, endovascular stents, and their delivery systems. Further validation of the model was provided by an evaluation of the safety and performance profile of final device prototypes, before their incorporation as commercially available products for clinical use, by an experienced neuroradiologist.

Although this model is appropriate for an acute assessment, the tortuous vascular path is positional; repositioning and manipulating the forelimb may likely alter the geometry of the endovascular implants over the bends. The caliber of the target vessel does not replicate the human ICA. The porcine arteries also have a higher propensity for vasospasm. We cannot replicate the bony encasement and the level of immobility experienced at the human carotid siphon. Nevertheless, despite these limitations, endovascular device testing in this territory provides a robust environment for a rigorous assessment of the delivery and deployment of endovascular devices in a technically less demanding and reproducible in vivo model.