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.

Histological and Biomechanical Characteristics of Human Decellularized Allograft Heart Valves After Eighteen Months of Storage in Saline Solution.

Background: The best storage preservation method for maintaining the quality and safety of human decellularized allograft heart valves is yet to be established. Objective: The aim of the present study was to evaluate the stability in terms of extracellular matrix (ECM) integrity of human heart valve allografts decellularized using sodium dodecyl sulfate-ethylenediaminetetraacetic acid (SDS-EDTA) and stored for 6, 12, and 18 months. Methods: A total of 70 decellularized aortic and pulmonary valves were analyzed across different storage times (0, 6, 12, and 18 months) for solution pH measurements, histological findings, cytotoxicity assay results, biomechanical test results, and microbiological suitability test results. Continuous data were analyzed using one-way analysis of variance comparing the follow-up times. Results: The pH of the stock solution did not change during the different time points, and no microbial growth occurred up to 18 months. Histological analysis showed that the decellularized allografts did not present deleterious outcomes or signs of structural degeneration in the ECM up to 12 months. The biomechanical properties showed changes over time in different aspects. Allografts stored for 18 months presented lower tensile strength and elasticity than those stored for 12 months (p < 0.05). The microbiological suitability test suggested no residual antimicrobial effects. Conclusion: Changes in the structure and functionality of SDS-EDTA decellularized heart valve allografts occur after 12 months of storage.

Decellularization as a method to reduce calcification in bovine pericardium bioprosthetic valves.

OBJECTIVES: Decellularization is an alternative method for processing biological tissues with decreased antigenicity and resistance to calcification. The aim of this study was to characterize the properties of decellularized (dCell) bovine pericardium fixed with 0.1% glutaraldehyde (GA) and to evaluate outcomes of bioprosthetic valves constructed with this tissue when implanted in the mitral position of juvenile sheep. METHODS: Bioprosthetic mitral valves were constructed with fresh bovine pericardium fixed in 0.5% GA (control group) or dCell bovine pericardium fixed in 0.1% GA (study group). Before implantation, samples were submitted to histological (haematoxylin-eosin, Movat and 4',6-diamidino-2-phenylindole), biochemical (residual deoxyribonucleic acid and α-gal epitopes) and biomechanical characterization. Valves were implanted (n = 8 in each group) as a mitral valve replacement for 180 days in sheep and explants were re-evaluated histologically and for calcification with radiological studies and calcium content determination. RESULTS: Unimplanted dCell pericardia exhibited a well-preserved extracellular matrix with absence of cells, a 77% reduction in deoxyribonucleic acid levels and with no detectable α-gal epitopes. When compared to controls, they had lower ultimate tensile strength (7.3 ± 5.4 vs 10.2 ± 3.0 mPa, P = 0.04) and greater percentage elongation in the longitudinal direction (29 ± 6.5% vs 23.8 ± 5.1%, P = 0.02). After 180 days in mitral position, dCell valves showed pliable leaflets without macroscopic signs of calcification. Histologically, dCell leaflets had intact collagen fibres, better tissue remodelling and a significant 89% reduction in calcium content. CONCLUSIONS: This study demonstrates that bioprosthetic valves constructed with dCell bovine pericardium fixed in low GA concentration were resistant to calcification and may thereby improve long-term durability of the tissue.

Human Heart Explant-Derived Extracellular Vesicles: Characterization and Effects on the In Vitro Recellularization of Decellularized Heart Valves.

Extracellular vesicles (EVs) are particles released from different cell types and represent key components of paracrine secretion. Accumulating evidence supports the beneficial effects of EVs for tissue regeneration. In this study, discarded human heart tissues were used to isolate human heart-derived extracellular vesicles (hH-EVs). We used nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM) to physically characterize hH-EVs and mass spectrometry (MS) to profile the protein content in these particles. The MS analysis identified a total of 1248 proteins. Gene ontology (GO) enrichment analysis in hH-EVs revealed the proteins involved in processes, such as the regulation of cell death and response to wounding. The potential of hH-EVs to induce proliferation, adhesion, angiogenesis and wound healing was investigated in vitro. Our findings demonstrate that hH-EVs have the potential to induce proliferation and angiogenesis in endothelial cells, improve wound healing and reduce mesenchymal stem-cell adhesion. Last, we showed that hH-EVs were able to significantly promote mesenchymal stem-cell recellularization of decellularized porcine heart valve leaflets. Altogether our data confirmed that hH-EVs modulate cellular processes, shedding light on the potential of these particles for tissue regeneration and for scaffold recellularization.

Structural assessments in decellularized extracellular matrix of porcine semilunar heart valves: Evaluation of cell niches.

Tissue-engineered heart valves aim to reproduce the biological properties of natural valves with anatomically correct structure and physiological performance. The closest alternative to creating an ideal heart valve substitute is to use decellularized porcine heart valves, due to their anatomy and availability. However, the immunological barrier and the structural maintenance limit the long-term physiological performance of decellularized porcine heart valves. This study investigated the extracellular matrix (ECM) structure of aortic and pulmonary porcine valves decellularized by a low concentration sodium dodecyl sulfate (SDS)-based method in order to determine the ECM scaffold (ECMS) conditions related to remodeling potential. To assess the structures of the leaflets and conduits of the heart valves, ECM components and their organization were evaluated by histology, biochemical analysis (BC), scanning electron microscopy, multiphoton microscopy, tensile test, immunofluorescence labeling (IF), and Raman microspectroscopy used to draw a profile of the cell niches. Histology and multiphoton imaging of decellularized aortic and pulmonary leaflets and conduits revealed a collagen and elastin histoarchitecture with rearrangement, loosening fibers, and glycosaminoglycan depletion confirmed by biochemistry quantification. The potential cytotoxicity of SDS residues was eliminated after 10 wash cycles. The mechanical properties of the structure of the valve indicated a functional resistance of decellularized ECM. The IF demonstrated the presence of basement membrane, suggesting a potential structure for host cell attachment. The RM analysis showed evidence of molecular interactions, suggesting conservation of the chemical composition, particularly among the protein molecular structures. The structural analyses performed in the semilunar porcine heart valves demonstrate that decellularized ECMS has structural properties that support physiological performance and potential host tissue integration. In fact, decellularized leaflet scaffolds were prone to cell interaction after human adipose-derived stromal cell seeding and culturing. Further analysis of biocompatibility, particularly the ECM-cell interaction, can elucidate the remodeling process, in preserved decellularized heart valve scaffold.

In vitro evaluation of bovine pericardium after a soft decellularization approach for use in tissue engineering.

Pericardial membrane derived from bovine heart tissues is a promising source of material for use in tissue-engineering applications. However, tissue processing is required for its use in humans due to the presence of animal antigens. Therefore, the purpose of this study was to evaluate the structural integrity and biocompatibility of the bovine pericardium (BP) after a soft decellularization process with a 0.1% sodium dodecyl sulfate (SDS) solution, with the aim to remove xenoantigens and preserve extracellular matrix (ECM) bioactivity. The decellularization process promoted a mean reduction of 77% of the amount of DNA in the samples in which cell nuclei staining was undetectable. The ECM content was maintained as mostly preserved after decellularization as well as its biomechanical properties. In addition, the decellularization protocol has proven to be efficient in removing the xenoantigen alpha-gal, which is responsible for immune rejection. The decellularized BP was noncytotoxic in vitro and allowed human adipose-derived stem cell (hASC) adhesion. Finally, after 7 days in culture, the tissue scaffold became repopulated by hASCs, and after 30 days, the ECM protein pro-collagen I was seen in the scaffold. Together, these characteristics indicated that soft BP decellularization with 0.1% SDS solution allows the acquirement of a bioactive scaffold suitable for cell repopulation and potentially useful for regenerative medicine.

Conventional culture method and qPCR using 16S rDNA for tissue bank: a comparison using a model of cardiac tissue contamination.

Real-time polymerase chain reaction (qPCR) using 16S rDNA is an alternative to conventional culture-based tests. The aim of this study was to compare the conventional culture method with qPCR using 16S rDNA in a model of cardiac tissue contamination. Samples of cardiac tissue for artificial contamination with Escherichia coli and control samples were submitted for DNA extraction, which was conducted by selective and alkaline lysis and purification steps. A standard curve for 16S rDNA was constructed to determine the efficiency and analytical sensitivity of the assay in concentrations from 106 to 102 c.f.u. ml-1 using TaqMan Master Mix. 16S rDNA was detected in all contaminated samples; however, it was not detected in the the final washing step solution of the sample with a bioburden of 102 c.f.u. ml-1. Using qPCR is a potential alternative to conventional culture for microbiological safety testing of allograft tissues for biobanking, reducing the time and labour input required.

Long-Term Results of Mitral Valve Repair.

INTRODUCTION: Current guidelines state that patients with severe mitral regurgitation should be treated in reference centers with a high reparability rate, low mortality rate, and durable results. OBJECTIVE: To analyze our global experience with the treatment of organic mitral regurgitation from various etiologies operated in a single center. METHODS: We evaluated all surgically treated patients with organic mitral regurgitation from 2004-2017. Patients were evaluated clinically and by echocardiography every year. We determined early and late survival rates, valve related events and freedom from recurrent mitral regurgitation and tricuspid regurgitation. Valve failure was defined as any mitral regurgitation ≥ moderate degree or the need for reoperation for any reason. RESULTS: Out of 133 patients with organic mitral regurgitation, 125 (93.9%) were submitted to valve repair. Mean age was 57±15 years and 52 patients were males. The most common etiologies were degenerative disease (73 patients) and rheumatic disease (34 patients). Early mortality was 2.4% and late survival was 84.3% at 10 years, which are similar to the age- and gender-matched general population. Only two patients developed severe mitral regurgitation, and both were reoperated (95.6% at 10 years). Freedom from mitral valve failure was 84.5% at 10 years, with no difference between degenerative and rheumatic valves. Overall, late ≥ moderate tricuspid regurgitation was present in 34% of the patients, being more common in the rheumatic ones. The use of tricuspid annuloplasty abolished this complication. CONCLUSION: We have demonstrated that mitral regurgitation due to organic mitral valve disease from various etiologies can be surgically treated with a high repair rate, low early mortality and long-term survival that are comparable to the matched general population. Concomitant treatment of atrial fibrillation and tricuspid valve may be important adjuncts to optimize long-term results.

Comparison of automated and conventional microbiological examination of donated human cardiac tissue in heart valve banking.

Most tissue banks use the conventional method; however, the automated method has advantages over the conventional method. The aim of this study was to compare the conventional and automated methods of culture in human cardiac tissue using an artificial contamination model. Myocardial samples were contaminated with sequential concentration (104 to 10-1 CFU/mL) with Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus and Candida albicans. Cultures were obtained from solution were the fragment was immersed and minced tissue, before and after the routine decellularization solution, with automated and conventional culture methods. Automated and conventional methods were compared and a p value ≤ 0.05 was considered significant. Staphylococcus aureus presented a significantly higher growth in the automated method, as well as faster than the conventional (p < 0.05). The positivity for growth in the automated method was higher in concentrated inoculum (> 102 CFU/mL) (p < 0.05). The growth in the automated method was significantly faster than conventional when inoculum concentration was above 103 CFU/mL. The automated culture method is faster than conventional method with a higher positivity in a contaminated model of myocardial and transport solution used in tissue banks.

Fresh decellularized versus standard cryopreserved pulmonary allografts for right ventricular outflow tract reconstruction during the Ross procedure: a propensity-matched study.

OBJECTIVES: Recent studies have shown favourable early results with decellularized allografts (DAs) for right ventricular outflow tract reconstruction during the Ross procedure. However, mid- and long-term outcome data are still scarce. The objective of this study was to compare the durability of fresh DAs with standard cryopreserved allografts (SCAs) in patients undergoing the Ross procedure. METHODS: Two hundred patients underwent the Ross procedure with DA and 202 with SCA. Using propensity score matching, mid- and long-term clinical outcome and echocardiographic allograft function over time were compared. RESULTS: One hundred and thirty DA patients (median age 28 years, 71.5% men, mean follow-up 4.2 ± 2.6 years) were matched with 130 SCA patients (median age 30 years, 69.2% men, mean follow-up 13 ± 4.5 years). After matching, there were no differences in baseline characteristics. In the matched DA vs SCA groups, actuarial 8-year freedom from allograft dysfunction (DA = 86.7% vs SCA = 87.3%, P = 0.183) and freedom from allograft reintervention (DA = 99.2% vs SCA = 97.6%, P = 0.642) were comparable. Longitudinal echocardiographic analyses showed a significantly lower progression rate of peak right ventricular outflow tract gradients in the DA group during the first 3 years after the operation. Absolute gradients over time were slightly lower in DA when compared with SCA, although 95% confidence intervals overlapped. CONCLUSIONS: Up to 8 years of follow-up, DA and SCA used for right ventricular outflow tract reconstruction in the Ross procedure are associated with comparably excellent clinical and haemodynamic outcome. Longer follow-up and dedicated echocardiographic studies are still necessary to confirm the long-term performance of the DAs.

Long-term results of mitral valve repair

Abstract Introduction: Current guidelines state that patients with severe mitral regurgitation should be treated in reference centers with a high reparability rate, low mortality rate, and durable results. Objective: To analyze our global experience with the treatment of organic mitral regurgitation from various etiologies operated in a single center. Methods: We evaluated all surgically treated patients with organic mitral regurgitation from 2004-2017. Patients were evaluated clinically and by echocardiography every year. We determined early and late survival rates, valve related events and freedom from recurrent mitral regurgitation and tricuspid regurgitation. Valve failure was defined as any mitral regurgitation ≥ moderate degree or the need for reoperation for any reason. Results: Out of 133 patients with organic mitral regurgitation, 125 (93.9%) were submitted to valve repair. Mean age was 57±15 years and 52 patients were males. The most common etiologies were degenerative disease (73 patients) and rheumatic disease (34 patients). Early mortality was 2.4% and late survival was 84.3% at 10 years, which are similar to the age- and gender-matched general population. Only two patients developed severe mitral regurgitation, and both were reoperated (95.6% at 10 years). Freedom from mitral valve failure was 84.5% at 10 years, with no difference between degenerative and rheumatic valves. Overall, late ≥ moderate tricuspid regurgitation was present in 34% of the patients, being more common in the rheumatic ones. The use of tricuspid annuloplasty abolished this complication. Conclusion: We have demonstrated that mitral regurgitation due to organic mitral valve disease from various etiologies can be surgically treated with a high repair rate, low early mortality and long-term survival that are comparable to the matched general population. Concomitant treatment of atrial fibrillation and tricuspid valve may be important adjuncts to optimize long-term results.

Decellularized Allografts for Right Ventricular Outflow Tract Reconstruction in Children.

OBJECTIVE: Determine the midterm outcomes of decellularized allografts for right ventricular outflow tract (RVOT) reconstruction in children less than 12 years of age. METHODS: The study included all consecutive patients submitted to RVOT reconstruction with decellularized allografts between June 2006 and June 2016. Besides clinical and echocardiographic control, 20 patients with more than five years of follow-up were evaluated with computed tomography (CT) scans to determine allograft diameters and calcium scores. Structural valve deterioration was defined as any peak gradient above 40 mm Hg and/or insufficiency of moderate or severe degree. Conduit failure was defined as the need for allograft reintervention. RESULTS: There were 59 patients with a median age of six years (range = 0.01-12 years). The most common operation was the Ross procedure (34%). Mean clinical follow-up was 5.4 (2.8) years and was 94% complete. At eight years, only two patients needed a reintervention, with a 90.9% freedom from this event. Structural valve deterioration occurred in 13 patients, 5 due to stenosis and 8 due to insufficiency, with a freedom from structural valve deterioration due to any cause of 64.9% at eight years. Late CT scans demonstrated the absence or minimal calcification of the conduits. CONCLUSIONS: Decellularized allografts for RVOT reconstruction in children were associated with a low incidence of structural valve deterioration and conduit failure. Although these results still need to be confirmed in larger series and with longer follow-up, our data suggest favorable outcomes, at least in the first decade after the operation.

20 years experience with the Ross operation in middle-aged patients: the autologous principle is still alive.

Objectives: Review our long-term results with the Ross operation in middle-aged patients. Methods: Between 1995 and 2016, 129 consecutive patients (106 males); mean age (47.2 ± 5.2 years) underwent a Ross operation. Right ventricular outflow tract (RVOT) reconstruction was performed with cryopreserved (n = 45) or decellularized allografts (n = 84). Mean follow-up was 8.4 ± 5.3 years (0.1 20.5 years). We analyzed early and late mortality, as well as valve related events and the need for reoperations. Results: Early mortality was 1.6% and late survival was 87.6% at 16 years. There were 4 reoperations on the pulmonary autograft (96% freedom at 16 years) and 2 on the pulmonary allografts (99% freedom at 16 years). The 16-year freedom from more than mild aortic insufficiency (AI) and a late root diameter >45 mm was 64% and 71%, respectively. Patients with the preoperative diagnosis of AI are at greater risk for these complications. Among the allografts, decellularized allografts showed superior freedom from structural valve dysfunction. Conclusions: The Ross operation in this cohort was associated with long-term survival similar to the general population and low incidence of reoperations. Patients with the preoperative diagnosis of AI are at increased risk for late autograft insufficiency and root dilatation. Decellularized allografts presented the best results for reconstruction of the RVOT. These results support the conclusion that the Ross operation has an important role in the treatment of middle-aged patients with aortic valve disease, especially those with pure aortic stenosis.