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The development of an ideal small-diameter conduit for use in vascular bypass surgery has yet to be achieved. The ongoing innovation in biomaterial design generates novel conduits that require preclinical assessment in vivo, and a number of animal models have been used for this purpose. This article examines the rationale behind animal models used in the assessment of small-diameter vascular conduits encompassing the commonly used species: baboons, sheep, pigs, dogs, rabbits, and rodents. Studies on the comparative hematology for these species relative to humans are summarized, and the hydrodynamic values for common implant locations are also compared. The large- and small-animal models are then explored, highlighting the characteristics of each that determine their relative utility in the assessment of vascular conduits. Where possible, the performance of expanded polytetrafluoroethylene is given in each animal and in each location to allow direct comparisons between species. New challenges in animal modeling are outlined for the assessment of tissue-engineered graft designs. Finally, recommendations are given for the selection of animal models for the assessment of future vascular conduits.

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The choice of a bioprosthetic valve (BV) or mechanical valve (MV) in middle-aged adults undergoing aortic valve replacement is a complex decision that must account for numerous prosthesis and patient factors. A systematic review and meta-analysis was performed to compare long-term survival, major adverse prosthesis-related events, anticoagulant-related events, major bleeding, reoperation, and structural valve degeneration in middle-aged patients receiving a BV or MV. A comprehensive search from six electronic databases was performed from their inception to February 2016. Results from patients aged less than 70 years undergoing aortic valve replacement with a BV or MV were included. There were 12 studies involving 8,661 patients. Baseline characteristics were similar. There was no significant difference in long-term survival among patients aged 50 to 70 or 60 to 70 years. Compared with MVs, BVs had significantly fewer long-term anticoagulant-related events (hazard ratio [HR] 0.54, p = 0.006) and bleeding (HR 0.48, p < 0.00001) but significantly greater major adverse prosthesis-related events (HR 1.82, p = 0.02), including reoperation (HR 2.19, p < 0.00001). The present meta-analysis found no significant difference in survival between BVs and MVs in patients aged 50 to 70 or 60 to 70 years. Compared with MVs, BVs have reduced risk of major bleeding and anticoagulant-related events but increased risk of structural valve degeneration and reoperation. However, the mortality consequences of reoperation appear lower than that of major bleeding, and recent advances may further lower the reoperation rate for BV. Therefore, this review supports the current trend of using BVs in patients more than 60 years of age.

Avoidance of aortic manipulation in anOPCABG may decrease the risk of post-operative stroke, especially in patients with higher stroke risk. In addition, the elimination of cardiopulmonary bypass may reduce the risk of short-term mortality, renal failure, atrial fibrillation, bleeding, and length of intensive care unit stay.

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Expanded polytetrafluoroethylene (ePTFE) vascular conduits with less than or equal to 6 mm internal diameter typically occlude due to a combination of thrombus formation and neointimal hyperplasia. We hypothesized that by layering the polymerized elastin precursor, human tropoelastin, in the synthetic vessel lumen we could mimic the internal elastic lamina and so maintain low thrombogenicity while significantly reducing smooth muscle cell proliferation. The luminal surfaces of ePTFE conduits were activated with plasma immersion ion implantation (PIII) treatment to facilitate covalent attachment of tropoelastin. Multilayered tropoelastin vessels (2TE) enhanced endothelial cell attachment and proliferation in vitro and were superior to materials lacking the protein. In an ovine carotid interposition model of graft compatibility, partially tropoelastin coated vessels (1TE) thrombosed at a greater rate than control ePTFE, but 2TE maintained the same patency as controls. 2TE showed a significant reduction in neointimal area down to 9.7 ± 5.2% (p < 0.05) in contrast to 32.3 ± 3.9% for ePTFE alone. This reduction was due to a halving of the number of smooth muscle cells present and a corresponding reduction in their proliferation. 2TE, but not 1TE, enhanced the vascular compatibility of these materials: while both tropoelastin presentations increased in vitro endothelialization, only 2TE displayed the dual benefits of maintained hemocompatibility and simultaneously suppressed neointimal hyperplasia in vivo. We conclude that 2TE surface modification provides a significant improvement over ePTFE vascular conduits in a pilot large animal model study and presents an attractive path toward clinical applications for reduced diameter vessels.