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Evaluation of Pressure Transmission and Intraaneurysmal Contents After Endovascular Repair Using the Trivascular Enovus ePTFE Stent Graft in a Canine Model of AAA

Robert L. Hynecek, MD, Susan M. Troccola, MD, Brian G. DeRubertis, MD, Rabih A. Chaer, MD, Evan J. Ryer, MD, Jason Choi, Steven Hsu, K. Craig Kent, MD and Peter L. Faries, MD
Cornell University, Weill Medical College, New York, NY

Objective: Endotension has been defined as persistently elevated pressure within the excluded sac of an abdominal aortic aneurysm (AAA) after endovascular repair in the absence of endoleak. Devices that use expanded polytetrafluoroethylene (ePTFE) have been associated with the development of endotension and continued AAA enlargement. In this study intraaneurysmal pressure and aneurysm content were evaluated after endovascular repair with the Trivascular ePTFE stent graft in a canine model.
Methods: Prosthetic PTFE aneurysms containing a solid-state, strain-gauge pressure transducer were implanted in the infrarenal aorta of 13 mongrel dogs (25-35 kg). A second pressure transducer was inserted into the native aorta for systemic arterial pressure measurement. The stent graft was then deployed to exclude the aneurysm via distal aortic access. Comparison was made between 3 distinct stent grafts: the Trivascular Enovus (non-porous ePTFE, 4 animals), the original Gore Excluder (porous ePTFE, 5 animals), and the Medtronic AneuRx (Dacron, 4 animals). Daily systemic and intra-AAA pressures were measured for 4 weeks. All intraaneurysmal pressures were indexed to the simultaneously measured systemic pressure. After 4 weeks the aorta and prosthetic aneurysm were harvested, photographed and processed for histological investigation using H&E and trichrome stain.
Results: Following exclusion, the mean arterial pressure (MAP) and pulse pressure (PP) within the AAA sac tapered to less than 20% of systemic pressure within 24 hours for all 3 stent graft types (Table). Significantly lower intraaneurysmal pressures were present in the Trivascular and AneuRx treated aneurysms as compared to those treated with the original Excluder stent graft. Histological analysis of the Trivascular treated aneurysms demonstrated intraluminal content characterized almost entirely by erythrocytes with few scattered white blood cells and rare fibrin that lacked organization or lamination; it did not have the characteristic appearance of acute or chronic thrombus suggesting exclusion from macrophages as well as serous blood components. This contrasted with the content of Excluder treated aneurysms which contained poorly organized thrombus with haphazardly arranged fibrin deposition suggestive of active remodeling, and AneuRx which demonstrated mature, well organized collagenous connective tissue.
Conclusions: Exclusion of the AAA with the Trivascular stent graft resulted in nearly complete elimination of intraaneurysmal pressure in this model. Histological analysis of the content of the aneurysm further suggested complete exclusion, including elimination of circulating clotting factors and macrophages. Ultimately, clinical evaluation will be necessary to demonstrate the effectiveness of this stent graft in preventing the development of endotension.