title: The development of endotension is associated with increased transmission of pressure and serous components in porous expanded polytetrafluoroethylene stent-grafts: characterization using a canine model.
abstract: OBJECTIVE
  This study used a canine model of abdominal aortic aneurysms (AAAs) to compare intra-aneurysmal pressure and thrombus formation after exclusion with Dacron and expanded polytetrafluoroethylene (ePTFE) stent-grafts.
  
  
  METHODS
  Prosthetic AAAs with implanted strain-gauge pressure transducers were treated by stent-graft exclusion using Food and Drug Administration-approved devices in 10 mongrel dogs: five Dacron (AneuRx) and five ePTFE (original Excluder). Intra-aneurysmal pressure was measured over 4 weeks after AAA exclusion and indexed to the systemic pressure, represented as a percentage of a simultaneously obtained systemic pressure (value = 1.0). Magnetic resonance imaging (MRI) of the intra-aneurysmal thrombus was performed at 1, 2, and 4 weeks after exclusion and expressed as a signal-to-noise ratio (S:N) to control for background signal intensity. Comparisons of pressures and S:N between the two stent-grafts was analyzed with the Student's t test. Intra-aneurysmal thrombus was characterized histologically.
  
  
  RESULTS
  In animals excluded with both Dacron and ePTFE stent-grafts, the intra-aneurysmal pressure was nonpulsatile and reduced to <30% of systemic pressure. Significantly greater pressure transmission was observed after AAA exclusion using ePTFE compared with Dacron stent grafts (systolic pressure: ePTFE, 0.28 +/- 0.12 vs Dacron, 0.11 +/- 0.02, P < .001; mean pressure: ePTFE, 0.16 +/- 0.08 vs Dacron, 0.06 +/- 0.02, P < .001). MRI confirmed the absence of perfusion in all aneurysms. The T1-weighted signal intensity remained persistently elevated (S:N at 1 week, 2.7 +/- 0.4 vs 2 weeks, 4.0 +/- 0.2 vs 4 weeks, 5.4 +/- 1.3) in ePTFE-treated intra-aneurysmal thrombus, suggesting an absence of thrombus organization. In contrast, progressive evolution of T1 signal intensity in aneurysms excluded by Dacron stent-grafts was consistent with maturation from intact red blood cells (S:N at 1 week, 3.3 +/- 0.4) to methemoglobin (S:N at 2 weeks, 6.1 +/- 0.8), and then hemosiderin and ferritin (S:N at 4 weeks, 2.4 +/- 0.5). Histologically, ePTFE-excluded aneurysms contained poorly organized thrombus with red blood cell fragments and haphazardly arranged fibrin deposition indicative of active remodeling and continued influx of transudated serum. In aneurysms excluded by Dacron stent-grafts, dense, mature collagenous connective tissue and organized fibrin were present, indicative of greater thrombus organization.
  
  
  CONCLUSIONS
  Stent-graft treatment reduces intra-aneurysmal pressure to <30% of systemic pressure when no endoleak is present; however, significantly greater pressure is present in aneurysms treated with porous ePTFE stent-grafts than Dacron grafts. Histologic and MRI imaging analysis suggest that active transudation of serous blood components may be contributing to this increased intra-aneurysmal pressure.
authors.affiliation: Department of Surgery, New York Presbyterian Hospital, Cornell University, New York, NY 10021, USA.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Trocciola
authors.forename: Rajeev
authors.initials: R
authors.lastname: Dayal
authors.forename: Rabih A
authors.initials: RA
authors.lastname: Chaer
authors.forename: Stephanie C
authors.initials: SC
authors.lastname: Lin
authors.forename: Brian
authors.initials: B
authors.lastname: DeRubertis
authors.forename: Evan J
authors.initials: EJ
authors.lastname: Ryer
authors.forename: Robert L
authors.initials: RL
authors.lastname: Hynececk
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Pierce
authors.forename: Martin
authors.initials: M
authors.lastname: Prince
authors.forename: Juan
authors.initials: J
authors.lastname: Badimon
authors.forename: Michael L
authors.initials: ML
authors.lastname: Marin
authors.forename: Valentin
authors.initials: V
authors.lastname: Fuster
authors.forename: K Craig
authors.initials: KC
authors.lastname: Kent
authors.forename: Peter L
authors.initials: PL
authors.lastname: Faries
mesh_terms: D000818:Animals; D017544:Aortic Aneurysm, Abdominal / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery*; D001807:Blood Vessel Prosthesis; D004195:Disease Models, Animal; D004285:Dogs; D004867:Equipment Design; D011093:Polyethylene Terephthalates; D011138:Polytetrafluoroethylene; D015607:Stents; D014160:Transducers, Pressure; D017211:Treatment Failure
chemical_list: D011093:Polyethylene Terephthalates; D011138:Polytetrafluoroethylene