Impact of Structural Valve Deterioration on Outcomes in the Cryopreserved Mitral Homograft Valve

A Literature Review on the Use of Aortic Allografts in Modern Cardiac Surgery for the Treatment of Infective Endocarditis: Is There Clear Evidence or Is It Merely a Perception?

Infective valve endocarditis is caused by different pathogens and 60% of those involve the aortic valve with valve failure. Although S. aureus is recognized as the most frequently isolated causative bacterium associated with IE in high-income countries, Gram-positive cocci nevertheless play a crucial role in promoting infection in relation to their adhesive matrix molecules. The presence of pili on the surface of Gram-positive bacteria such as in different strains of Enterococcus faecalis and Streptococcus spp., grants these causative pathogens a great offensive capacity due to the formation of biofilms and resistance to antibiotics. The indications and timing of surgery in endocarditis are debated as well as the choice of the ideal valve substitute to replace the diseased valve(s) when repair is not possible. We reviewed the literature and elaborated a systematic approach to endocarditis management based on clinical, microbiological, and anatomopathological variables known to affect postoperative outcomes with the aim to stratify the patients and orient decision making. From this review emerges significant findings on the risk of infection in the allograft used in patients with endocarditis and no endocarditis etiology suggesting that the use of allografts has proved safety and effectiveness in patients with both pathologies.

Tissue-engineered mitral valve: morphology and biomechanics †

OBJECTIVES

The present study aimed at developing tissue-engineered mitral valves based on cell-free ovine mitral allografts.

METHODS

The ovine mitral valves (OMVs) (n = 46) were harvested in the local slaughter house. They were decellularized using detergent solutions and DNase. The effectiveness of decellularization was assessed by histological (haematoxylin-eosin, Movat's pentachrome) and immunofluorescent staining (for DNA and α-Gal), and DNA-quantification. To reveal the receptiveness of decellularized tissue to endothelial cells (ECs), the valve leaflets were reseeded with ovine ECs, derived from endothelial progenitor cells in vitro. For assessment of biomechanical properties, uniaxial tensile tests were carried out.

RESULTS

Histology and immunofluorescent staining revealed absence of cell nuclei in decellularized leaflets, chordae and papillary muscles. According to the software for immunofluorescence analysis, reduction in DNA and α-Gal was 99.9 and 99.6%, respectively. DNA-quantification showed 71.2% reduction in DNA content without DNase and 96.4% reduction after DNase treatment. Decellularized leaflets were comparable with native in ultimate tensile strain (native, 0.34 ± 0.09 mm/mm, vs decellularized, 0.44 ± 0.1 mm/mm; P = 0.09), and elastin modulus (native, 0.39 ± 0.27, vs decellularized, 0.57 ± 0.55, P = 0.46), had increased ultimate tensile stress (native, 1.23 ± 0.35 MPa, vs decellularized 2.12 ± 0.43 MPa; P = 0.001) and collagen modulus (native, 5.5 ± 1.26, vs decellularized, 8.29 ± 2.9; P = 0.04). After EC seeding, immunofluorescent staining revealed a monolayer of CD31-, eNOS- and vWF-positive cells on the surface of the leaflet, as well as a typical cobble-stone morphology of those cells.

CONCLUSIONS

Decellularization of ovine mitral valve results in a mitral valves scaffold with mechanical properties comparable with native tissue, and a graft surface, which can be repopulated by endothelial cells.