Investigation of Reduced Permeability Expanded Polytetrafluoroethylene Graft Material for Endovascular Aortic Aneurysm Repair Using a Canine Model

Introduction: Successful endovascular repair of AAA (EVAR) depends on the exclusion of arterial perfusion and pressurization of aneursym sac. Prior clinical evaluation of the original Gore Excluder (ePTFE) for EVAR demonstrated an increased prevalence of endotension likely from increased permeability. This study evaluates the pressure transmission through a new, low permeable Gore ePTFE stent graft as compared with a low permeable Dacron stent graft. Methods: Prosthetic ePTFE aneurysms, each containing a solid-state, strain-gauge pressure transducer, were implanted in the infrarenal aorta of 9 mongrel dogs. A second pressure transducer was inserted into the native aorta for systemic arterial pressure measurement (Figure 1). The stent graft was then deployed to exclude the aneurysm via distal aortic access. Comparison was made between two stent grafts: the Medtronic AneuRx (low permeable dacron; four animals) and the Gore Excluder (low permeable ePTFE; five animals) Daily systemic and intra-AAA pressures were measured for 4 weeks. Intra-aneurysmal pressures were indexed to simultaneously measured systemic pressures. Absence of endoleak was confirmed both angiographically and by CT scan. After 4 weeks the prosthetic aneurysm, aorta, and its contents were harvested and processed for histologic investigation with hemotoxylin and eosin staining. Postoperative aneurysm sac and systemic pressure measurements were obtained daily for 28 days. The animals were subsequently euthanized. The prosthetic aneurysm sacs were harvested and the tissue characterized histologically using H & E, trichrome, and Mallory's phosphotungstic acid-hematoxylin (PTAH) stains. Results: Within 24 hours after exclusion, the mean arterial pressure and pulse pressure within the AAA sac reduced to less than 20% of systemic pressure for both graft types. For the remainder of the post-operative period equivalently lower indexed intra-aneurysmal pressures were present in the low permeable Excluder device as well as the AneuRx treated aneurysms (AneuRx 0.08±0.03 vs new Excluder 0.06±0.02, P< 0.001) Pressure data for the new Excluder device is shown in Figure 2. Histologic investigation was also performed demonstrating mature, well-organized collagenous connective tissues in the AneurRx dacron grafts. This is contrasted with the slightly disorganized fibrin deposition found in the new excluder devices. Conclusion: The new low permeable Gore ePTFE graft significantly reduced the intra-aneurysmal pressure as compared to the original Gore graft. These pressure readings were eqivalent to the low porosity, commercially available dacron stent grafts. This correlates with clinical data indicating decreased sac size and no progression in sac expansion in the abscence of an endoleak.