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OBJECTIVE: While extracellular xenograft repair has produced encouraging results when applied to cardiac, valvular, and specific aortic defects, its employment as a tube graft to replace the ascending aorta has not been reported. We describe a patient who underwent resection and replacement of an infected ascending aortic graft with an extracellular matrix (ECM) conduit. The patient did well, but 14 months later developed a pseudoaneurysm from the staple line used to construct the ECM conduit. The ECM graft was subsequently explanted and replaced with Dacron. There was no residual infection. We present histological and mechanical properties of the explanted ECM material (Figure 1).
METHODS: Explanted ECM material was examined and compared with unused control material. Histological examination included Annexin V, c-Kit (C-19), elastin, and CD45. Mechanical testing utilized the Enduratec 3200 Tensile system (Bose Corporation, Eden Prairie, MN). ECM segments were preconditioned for 10 cycles, then pulled in tension, at a rate of 0.15 mm/sec, until failure while recording time, load, and displacement.
RESULTS: We observed no remarkable histological differences between explanted and control specimens; both had similar cellular components. There was a lack of infiltrating or repopulating cells within the explanted matrix. No dissection, delamination, or breakdown of material was noted. Mechanical testing of control ECM demonstrated an elastic modulus of 42.9±11.6 MPa (n=5). Elastic modulus of the explanted sample was 6.6 MPa in the circumferential direction and 13.0 MPa in the longitudinal direction (native ascending thoracic aorta range: 2.0-6.5 MPa).
CONCLUSIONS: Our experience suggests that its superior strength, handling characteristics, and resistance to infection make ECM scaffold a possible alternative conduit to cryopreserved homografts. We were surprised the explanted sample did not show endothelialization, which is inconsistent with reports of post-implant ECM transformation. Applicability as an aortic conduit merits further investigation to better understand behavior of ECM in this situation. Long-term durability data is also needed, especially for shear stress and ideal securing techniques when implanted as primary grafts in high-pressure vascular systems.