The impact of heart valve and partial heart transplant models on the development of banking methods for tissues and organs: A concise review.

Cryopreserved human heart valves fill a crucial role in the treatment for congenital cardiac anomalies, since the use of alternative mechanical and xenogeneic tissue valves have historically been limited in babies. Heart valve models have been used since 1998 to better understand the impact of cryopreservation variables on the heart valve tissue components with the ultimate goals of improving cryopreserved tissue outcomes and potentially extrapolating results with tissues to organs. Cryopreservation traditionally relies on conventional freezing, employing cryoprotective agents, and slow cooling to sub-zero centigrade temperatures; but it is plagued by the formation of ice crystals and cell damage upon thawing. Researchers have identified ice-free vitrification procedures and developed a new rapid warming method termed nanowarming. Nanowarming is an emerging method that utilizes targeted application of energy at the nanoscale level to rapidly rewarm vitrified tissues, such as heart valves, uniformly for transplantation. Vitrification and nanowarming methods hold great promise for surgery, enabling the storage and transplantation of tissues for various applications, including tissue repair and replacement. These innovations have the potential to revolutionize complex tissue and organ transplantation, including partial heart transplantation. Banking these grafts addresses organ scarcity by extending preservation duration while preserving biological activity with maintenance of structural fidelity. While ice-free vitrification and nanowarming show remarkable potential, they are still in early development. Further interdisciplinary research must be dedicated to exploring the remaining challenges that include scalability, optimizing cryoprotectant solutions, and ensuring long-term viability upon rewarming in vitro and in vivo.

Cryopreserved human heart valve allografts: a ten-year single centre experience.

This study provides an overview of tissue banking activities at the Croatian Cardiovascular Tissue Bank (CTB) during past ten years and presents the outcomes of cryopreserved heart valve allografts (CHAs) use in different patient groups. From June 2011 until December 2021, 75 heart donations were referred to CTB: 41 recipient of heart transplant (RHT), 32 donors after brain death (DBD) and 2 donors after circulatory death (DCD) donations. Processing resulted in 103 valves of which 65 met quality requirements for clinical use. Overall tissue discard rate was 37%. The most frequent reasons for discard were inadequate morphology (12%) in RHT donations and microbiological contamination (19%) in DBD donations. Altogether, 38 CHAs were transplanted to 36 patients. Recipients were divided in three groups; infective endocarditis (IE), non-infectious heart disease and congenital heart disease group. In the IE group, the 30-day, 1-year and 3-year survival was 71%, 53% and 47%, respectively. Freedom from re-operation due to all graft-related causes was 76% and due to structural valve deterioration 88%. There were no cases of graft reinfection. In the congenital heart disease group CHAs were predominantly (94%) used for right ventricular outflow tract reconstruction and 88% of patients recovered without graft-related complications. At present, the number of demands for CHAs at CTB considerably outweighs their availability.

Hyaluronic Acid-Grafted Bioprosthetic Heart Valves Achieved by Copolymerization Exhibited Improved Anticalcification and Antithrombogenicity.

Bioprosthetic heart valves (BHVs) are widely used in clinic, but they still have problems of calcification, thrombogenicity, and cytotoxicity. The reported techniques based on glutaraldehyde (Glut) crosslinking have difficulty in solving these problems simultaneously. In this study, we grafted Glut-crosslinked porcine pericardium (GA) with hyaluronic acid (HA) by radical copolymerization to improve its anticalcification and antithrombotic properties. Partially methacrylated poly-ε-lysine was used to introduce methacryl groups into GA. Then, HA-grafted porcine pericardium (GA-HA) was obtained by radical copolymerization. Rat's subcutaneous implantation results showed that the calcium content of GA-HA was significantly lower than that of GA (37 ± 29 µg/mg vs 188 ± 7 µg/mg), and the platelets adhering to the surface of GA-HA decreased by approximately 41% compared with GA. In conclusion, grafting porcine pericardium with HA by copolymerization might be feasible to improve the anticalcification and antithrombotic properties of BHVs.

Structural Integrity and Cellular Viability of Cryopreserved Allograft Heart Valves in Right Ventricular Outflow Tract Reconstruction: Correlation of Histopathological Changes with Donor Characteristics and Preservation Times.

INTRODUCTION: Cryopreserved allograft heart valves (CAHV) show longer event-free survival compared to other types of protheses. However, all patients develop early and/or late allograft failure. Negative predictors are clinical, and there is a lack of evidence whether they correspond with the microscopic structure of CAHV. We assessed histopathological signs of structural degeneration, degree of cellular preservation, and presence of antigen-presenting cells (APC) in CAHV and correlated the changes with donor clinical characteristics, cryopreservation times, and CAHV types and diameters. METHODS: Fifty-seven CAHV (48 pulmonary, nine aortic) used for transplantation between November/2017 and May/2019 were included. Donor variables were age, gender, blood group, height, weight, and body surface area (BSA). Types and diameters of CAHV, cold ischemia time, period from decontamination to cryopreservation, and cryopreservation time were recorded. During surgery, arterial wall (n=56) and valvar cusp (n=20) samples were obtained from the CAHV and subjected to microscopy. Microscopic structure was assessed using basic staining methods and immunohistochemistry (IHC). RESULTS: Most of the samples showed signs of degeneration, usually of mild degree, and markedly reduced cellular preservation, more pronounced in aortic CAHV, correlating with arterial APC counts in both basic staining and IHC. There was also a correlation between the degree of degeneration of arterial samples and age, height, weight, and BSA of the donors. These findings were independent of preservation times. CONCLUSION: CAHV show markedly reduced cellular preservation negatively correlating with the numbers of APC. More preserved CAHV may be therefore prone to stronger immune rejection.

Immune Privilege of Heart Valves.

Immune privilege is an evolutionary adaptation that protects vital tissues with limited regenerative capacity from collateral damage by the immune response. Classical examples include the anterior chamber of the eye and the brain. More recently, the placenta, testes and articular cartilage were found to have similar immune privilege. What all of these tissues have in common is their vital function for evolutionary fitness and a limited regenerative capacity. Immune privilege is clinically relevant, because corneal transplantation and meniscal transplantation do not require immunosuppression. The heart valves also serve a vital function and have limited regenerative capacity after damage. Moreover, experimental and clinical evidence from heart valve transplantation suggests that the heart valves are spared from alloimmune injury. Here we review this evidence and propose the concept of heart valves as immune privileged sites. This concept has important clinical implications for heart valve transplantation.

Xenotransplantation of decellularized pig heart valves-Regulatory aspects in Europe.

BACKGROUND: The lack of human donors for allotransplantation forces the development of other strategies to circumvent the existing organ shortage documented on the waiting lists. Here, xenotransplantation offers a suitable option since the genetic modification of animals has become an established method that allows the generation of animals as donors of cells, tissues, and organs with reduced antigenicity. METHODS: Focus is given on the generation of decellularized matrix scaffolds, for example, for valve transplantation and/or repair, that have the potential being fully assimilated by the recipient as they are no longer a mechanical implant with risk of calcification and related failure. RESULTS: This new class of products is transplants that will be regulated either as medical devices or as cell-based medicinal products, that is, advanced therapy medicinal products, according to the regulations in the European Union. CONCLUSIONS: In this review, we compile relevant regulatory aspects and point out the possibilities of how these products for human use may be regulated in the future.

Studying Xenograft Rejection of Bioprosthetic Heart Valves.

Millions of patients with valvular heart disease have benefitted from heart valve replacement since the procedure was first introduced in the 1960s; however, there are still many patients who get early structural valve deterioration (SVD) of their bioprosthetic heart valves (BHV). BHV are porcine, bovine, or equine tissues that have been glutaraldehyde fixed to preserve the tissue and presumably make the tissue immunologically inert. These glutaraldehyde-fixed BHV with anti-calcification treatments last long periods of time in older adults but develop early SVD in younger patients. The consensus at present is that the early SVD in younger patients is due to more "wear and tear" of the valves and higher calcium turnover in younger patients. However, as younger patients likely have a more robust immune system than older adults, there is a new hypothesis that BHV xenografts may undergo xenograft rejection, and this may contribute to the early SVD seen in younger patients.At present, the technology to noninvasively study in vivo whether an implanted BHV in a human patient is undergoing rejection is not available. Thus, a small animal discordant xenotransplant model in young rodents (to match the young patient getting a pig/bovine/equine BHV) was developed to study whether the hypothesis that glutaraldehyde-fixed BHV undergo xenograft rejection had any merit. In this chapter, we describe our model and its merits and the results of our investigations. Our work provides clear evidence of xenograft rejection in glutaraldehyde-fixed tissue, and our small animal model offers an opportunity to study this process in detail.

Trilayer scaffold with cardiosphere-derived cells for heart valve tissue engineering.

Natural polymers collagen, glycosaminoglycans, and elastin are promising candidate materials for heart valve tissue engineering scaffolds. This work produced trilayer scaffolds that resembled the layered structures of the extracellular matrices of native heart valves. The scaffolds showed anisotropic bending moduli (in both dry and hydrated statuses) depending on the loading directions (lower in the With Curvature direction than in the Against Curvature direction), which mimicked the characteristic behavior of the native heart valves. The interactions between cardiosphere-derived cells and the scaffolds were characterized by multiphoton microscopy, and relatively similar cell distributions were observed on different layers (a cell density of 3,000-4,000 mm-3 and a migration depth of 0.3-0.4 mm). The trilayer scaffold has represented a forwarding step from the previous studies, in attempting to better replicate a native heart valve structurally, mechanically, and biologically.

Anaerobic bioburden in transport solution of human cardiovascular tissues.

Although reports of infections caused by anaerobes after tissue transplantation are uncommon, contamination of allografts may result in substantial complications. Anaerobic incubation and testing of organ transport solution (TS) are not routine. The aim of this study was to determine the bioburden of strict anaerobic bacteria and oxygen tension of heart-TS. Forty TS from different donors were evaluated cultured using membrane filtration (MF), direct inoculation on broth and automated blood culture bottle (ABCB). Bacterial identification was performed by MALDI-TOF. The transport conditions were simulated to verify the bacterial recovery. A sterile bag fulfilled with 250 ml-1 of sterile saline was spiked with 100 CFU ml-1 of Clostridium perfringens and the fluid recovered 0 h, 1 h, 2 h, 6 h, 12 h, 24 h and 48 h for culture and oxygen measurement. Strict anaerobic bacteria were not isolated in heart-TS. The recovery of C.perfringens spiked in heart-TS was 100% using automated blood culture bottles. MF method detected >100 CFU only after 6 h of spiking. The manual culture was not able to recover C.perfringens after the process. The percentage of O2 measures varied from 77.6 to 87.9%. MF or ABCB are better than direct inoculation for recovery of anaerobes from heart-TS. Although all samples from heart donors were negative for anaerobes (probably due to low incidence of contamination), C.perfringens were all recovered in the simulated transport condition.

Successful Truncal Valve Replacement After Truncal Valve Repairs.

The surgical management of severe truncal valvular dysfunction is still challenging in neonates with persistent truncus arteriosus. This report describes a 14-day-old neonate with severe truncal valve insufficiency successfully undergoing truncal valve repairs, and followed by valve replacement at the age of 4 years. The truncal valve was quadricuspid with two large and two small leaflets, and all leaflets had severe dysplastic and myxomatous changes. We performed leaflet extension and bicuspidization valvuloplasty for this valve. This patient obtained somatic growth for 4 years without heart failure symptoms, and safely underwent prosthetic valve replacement. This technique would be effective for truncal valve dysfunction in neonates as the life-saving and the bridging procedure to valve replacement.

Significant variation in heart valve banking practice.

The European Blood Alliance (EBA) Tissue and Cells annual benchmarking exercise identified that in 2014, the heart valve (HV) discard rate in tissue establishments (TEs) run by EBA members was between 19 and 65%. Given this significant discard rate, a decision was taken to carry out a worldwide data-gathering exercise to assess the processing methodology in different TEs. In collaboration with the Foundation of European Tissue Banks, a questionnaire asking for the details on HV processing was sent to TEs worldwide. Nineteen questionnaires were received back from 15 European TEs and 4 non-European TEs. The data provided confirmed a significant discard rate of HVs with 43-50% of aortic valves and 20-32% of pulmonary valves being discarded in 2015. The causes of HV discard varied, with microbiology contamination, anatomical and medical reasons being the main causes. This data-gathering exercise highlighted significant variations in practice in different TEs including how donor suitability is assessed, critical timings for heart retrieval and processing, heart rinsing, HV decontamination protocols and methods of microbiological testing. To reduce the discard rates, there are several aspects of HV banking that could be validated and standardised. Here, we report the findings of this data-gathering exercise. We consider this a first step that will help lead to standardising HV banking.

Validation of microbiological testing in cardiovascular tissue establishments: results of a second international quality-round trial.

The performance of many laboratories can be evaluated by participation in external quality assessment (EQA) schemes. EQA allows for comparison of a laboratory's performance with a source outside the laboratory-either a peer group of laboratories or a reference laboratory. Such EQA schemes do not exist in tissue banking despite the fact that tissue establishments (TE) perform very complex procedures. This paper describes the first ever EQA scheme in the field specifically assessing microbiological aspects in heart valve (HV) banking. Twenty-two TEs participated. Three HV tissue samples were sent to each participating TE-two contaminated with non-pathogenic micro-organisms and a third negative control. The aims were to isolate and identify the micro-organisms present and then to successfully decontaminate the HV tissue using the routine standard operating procedures of the TE. Eight of the TEs were able to isolate and identify all contaminating micro-organisms present, and of these, five also successfully decontaminated the tissue; 13 TEs failed to establish the identity of one or more of the contaminants; five TEs appear to have introduced contamination during the processing or testing of the tissue; and eight failed to successfully decontaminate the HV tissue. This initiative provides TEs with an international benchmark for tissue product microbiology testing. It has identified significant variation in practice and in the ability of different TEs to identify the presence of contamination. There is now work ongoing with the aim of setting up a regular EQA scheme for HV banking.

Hybrid Pericardium with VEGF-Loaded Hyaluronic Acid Hydrogel Coating to Improve the Biological Properties of Bioprosthetic Heart Valves.

Bioprosthetic heart valves (BHVs) used in the clinic are mostly fixed by glutaraldehyde and the lack of endothelialization is a major problem for glutaraldehyde-fixed pericardia. Hyaluronic acid is a major glycosaminoglycan that exists in native heart valves. Coupled with its inherent biocompatibility, it may enhance endothelial adhesion and proliferation when associated with vascular endothelial growth factor (VEGF). In this study, an optimized system is developed to improve the endothelialization of glutaraldehyde-fixed pericardium. A hybrid pericardium with VEGF-loaded hyaluronic acid hydrogel coating is developed by the crosslinking of 1,4-butanediol diglycidyl ether. The adhesion and growth potential of human umbilical vein endothelial cells (HUVECs) on pericardia, platelet adhesion, and calcification by an in vivo rat subdermal implantation model are investigated. The results show improved HUVEC adhesion and proliferation, less platelet adhesion, and less calcification for hybrid pericardium by introducing the coating of VEGF-loaded hyaluronic acid hydrogel. Thus, the coating of VEGF-loaded hyaluronic acid hydrogel on pericardium is a promising approach to obtain bioprosthetic valves for clinical applications with increased endothelialization and antithrombotic and anticalcification properties.

EGCG and enzymatic cross-linking combined treatments for improving elastin stability and reducing calcification in bioprosthetic heart valves.

The failures of glutaraldehyde (GLUT) cross-linked bioprosthetic heart valves (BHVs) are mainly due to degeneration and calcification. In this study, we developed a new preparation strategy for BHVs named as "HPA/EDC/EGCG" that utilized 3,4-hydroxyphenylpropionic acid (HPA)-conjugated pericardium, epigallocatechin gallate (EGCG), and horseradish peroxidase (HRP)/hydrogen peroxide (H2 O2 ) enzymatic cross-linking. HPA-pericardium conjugation was done by carbodiimide coupling reaction using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). Then HPA-conjugated pericardium was cross-linked by HRP/H2 O2 enzyme-catalyzed oxidation. The feeding ratios of HPA and EGCG were optimized. The consumption of amino groups, collagenase and elastase degradation in vitro, biomechanics, extracellular matrix stability, and calcification of HPA-/EDC-/EGCG-treated pericardiums were characterized. We demonstrated that HPA-/EDC-/EGCG-treated pericardiums had better elastin stabilization and less calcification. EGCG and enzymatic cross-linking treated pericardiums showed improved mechanical properties. This new EGCG and enzymatic cross-linking strategy would be a promising method to make BHVs with better elastin stability and anti-calcification property. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1551-1559, 2019.

Anticoagulation in a patient with antiphospholipid syndrome and a mechanical heart valve: a case study.

: A case report of a patient with antiphospholipid syndrome (APS) with positive lupus anticoagulant and a mechanical mitral valve replacement (MVR) who presented with a thrombosis and difficult-to-control INRs. Current literature on anticoagulation options for patients who present with these conditions as well as alternate laboratory assays are reviewed. APS can present a unique complexity and challenge to appropriate anticoagulation on warfarin. Although there are emerging data regarding the use of novel oral anticoagulants to treat this condition, they do not justify their use in a patient with APS and an MVR because of a current lack of evidence. CFX testing may be used to calibrate INRs when there is a concern for false readings because of lupus anticoagulant interaction with INR assays.

Valve-sparing root replacement for freestanding pulmonary autograft aneurysm after the Ross procedure.

OBJECTIVE: Autograft dilatation is the main long-term complication following the Ross procedure using the freestanding root replacement technique. We reviewed our 25-year experience with the Ross procedure with a special emphasis on valve-sparing reoperations. METHODS: From 1991 to 2016, 153 patients (29.6 ± 16.6 years; 29.4% pediatric) underwent a Ross operation at our institution with implantation of the autograft as freestanding root replacement. The follow-up is 98.7% complete with a mean of 12.2 ± 5.5 years. RESULTS: Mortality at 30-days was 2.0%. Echocardiography documented no or trivial aortic regurgitation in 99.3% of the patients at discharge. Survival probability at 20 years was 85.4%. No case of autograft endocarditis occurred. Autograft deterioration rate was 2.01% per patient-year, and freedom from autograft reoperation was 75.3% at 15 years. A reoperation for autograft aneurysm was required in 35 patients (22.9%) at a mean interval of 11.1 ± 4.6 years after the Ross procedure. A valve-sparing root replacement was performed in 77% of patients, including 10 David and 17 Yacoub procedures with no early mortality. Three patients required prosthetic valve replacement within 2 years after a Yacoub operation. At latest follow-up, 92% of all surviving patients still carry the pulmonary autograft valve. Freedom from autograft valve replacement was 92.1% at 15 years. CONCLUSIONS: Using the David or Yacoub techniques, the autograft valve can be preserved in the majority of patients with root aneurysms after the Ross procedure. Reoperations can be performed with no early mortality, a good functional midterm result, and an acceptable reintervention rate.

Bioburden in transport solutions of human cardiovascular tissues: a comparative evaluation of direct inoculation and membrane filter technique.

All cardiac allograft tissues are under potential contamination, requiring a validated terminal sterilization process or a minimal bioburden. The bioburden calculation is important to determine the bacterial burden and further decontamination and disinfection strategies for the valve processing. The aim of this study was to determine the bioburden from transport solution (TS) of heart valves obtained from non-heart-beating and heart-beating donors in different culture methods. The bioburden from TS was determined in 20 hearts donated for valve allograft tissue using membrane filter (MF) and direct inoculation. Tryptic soy agar and Sabouraud plates were incubated and colonies were counted. Ninety-five percent of samples from this study were obtained from heart-beating donors. The warm ischemic time period for heart was 1.06 ± 0.74 h and the cold ischemic time period was 25.66 ± 11.16 h. The mean TS volume was 232.68 ± 96.67 mL (48.5-550 mL). From 20 samples directly inoculated on TSA agar plates, 2 (10%) were positive. However, when MF was used, from 20 samples in TSA, 13 (65%) were positive with a mean count of 1.36 ± 4.04 CFU/mL. In Sabouraud plates, the direct inoculation was positive in 5 samples (25%) with a mean count of 0.24 ± 0.56 CFU/mL. The use of MF increased the positivity to 50% (10 samples from a total of 20) with a mean of 0.28 ± 0.68 CFU/mL. The positivity was superior using MF in comparison with direct inoculation (p < 0.05). The bioburden of TS is low and MF is the technique of choice due to higher positivity.

Morphology, Clinicopathologic Correlations, and Mechanisms in Heart Valve Health and Disease.

The clinical and pathological features of the most frequent intrinsic structural diseases that affect the heart valves are well established, but heart valve disease mechanisms are poorly understood, and effective treatment options are evolving. Major advances in the understanding of the structure, function and biology of native valves and the pathobiology, biomaterials and biomedical engineering, and the clinical management of valvular heart disease have occurred over the past several decades. This communication reviews contemporary considerations relative to the pathology of valvular heart disease, including (1) clinical significance and epidemiology of valvular heart disease; (2) functional and dynamic valvular macro-, micro- and ultrastructure; (3) causes, morphology and mechanisms of human valvular heart disease; and (4) pathologic considerations in valve replacement, repair and, potentially, regeneration of the heart valves.