Fourteen-year experience with homovital homografts for aortic valve replacement

Partial Heart Transplantation: Early Experience With Pediatric Heart Valve Replacements That Grow

Heart valve replacement in children is fraught with long-term morbidity and mortality rates, largely because conventional implants lack the capacity to grow with the child. Partial heart transplantation presents a potential solution by transplanting only specific segments of a donor heart, thereby providing a living and growing heart valve implant. This approach harnesses the full spectrum of cardiac tissues, which, when freshly procured and supported by immunosuppression, can integrate as functional and potentially growth-capable tissue. This state-of-the-art review discusses the history and development of partial heart transplantation, its indications, recent clinical experiences, regulation, and future directions.

Heart Valve Replacement in Children: Homografts to Partial Heart Transplantation

Congenital valvular abnormalities in pediatric patients represent a complex surgical problem that carries with it significant morbidity and mortality. Repair of native valves may not always be feasible, leading to requisite surgical intervention. This has led to the development of mechanical valves, bioprosthetic valves, homografts, stented valves, the Ross operation, and finally, the ultimate development of partial heart transplantation. Each technique carries with it potential benefits and limitations. A comprehensive literature search in concert with expert opinion was completed. This yielded a total of 35 applicable references, with the goal to describe the indications, benefits, and risks associated with each approach. Pediatric patients present a unique problem when considering intervention for irreparable valvular abnormalities. Each technique provides a unique opportunity for mitigation of extant pathology but carries with it potential for risks that are inherent to the approach and must be considered. Partial heart transplant is the only technique which provides the opportunity for definitive valvular replacement in pediatric patients. Although each technique does provide an opportunity to resolve congenital valvular disease, the development of partial heart transplantation is a revolutionary technique that is unique in its ability to grow with the patient. The remaining techniques, at a minimum, require further intervention as the patient grows and develops. Although the literature is clear that there are a variety of options available to surgeons, there is only 1 which can resolve congenital valvular disease with 1 operation.

Partial Heart Transplant Update: Where Are We In 2025?

Partial heart transplantation (PHT) creates a new and innovative approach to allow for patient and disease tailored intervention with the ability to treat a larger patient base. It offers the growth capacity of a heart transplantation without the need for high dose immunosuppression. The importance of a valve replacement with the potential of growth is imperative in the pediatric population as these patients will otherwise outgrow their new valves requiring repeat and high-risk interventions. Adaptive valve growth has been observed prior to PHT, in the case of orthotopic heart transplantation and Ross pulmonary autografts. The first human PHT was performed in April of 2022 at Duke. The recipient was a 17-day old infant with truncus arteriosus and severe truncal valve regurgitation. The operation was a success and the transplanted PHT conduit showed appropriate adaptive valve growth. Due to the low immunogenicity and recipient endothelialization of the transplanted PHT graft, the immunosuppressive requirements for PHT patients are low. One of the benefits of PHT is that it utilizes hearts which would otherwise not be suitable for orthotopic heart transplantation. Furthermore, the prospect of domino and split root PHT increases the potential of ethical and efficient organ stewardship. Currently PHT is regulated by the Food and Drug Administration, a ruling which was released in early 2024 as human cells, tissues, or cellular or tissue-based products (HCT/Ps). This means it does not compete with hearts suitable for orthotopic heart transplantation which are regulated as organs under the Organ Procurement and Transplantation Network (OPTN).

Partial Heart Transplantation Promotes Organ Stewardship: Domino Hearts and Split Roots

Background

Partial heart transplantation (PHT) has emerged as a pioneering approach for treating infants with irreparable heart valve dysfunction. However, the scarcity of suitable donors presents a significant bottleneck to its widespread application. This study introduces and evaluates the novel use of domino and split-root procedures within PHT.

Methods

We describe 6 pediatric cardiac patients who underwent either domino or split-root PHT at our institution.

Results

From May to August 2023, our team successfully executed 3 domino and 3 split-root PHTs, including 1 procedure that involved interinstitutional collaboration. These cases highlight the procedural feasibility and the potential for broader application.

Conclusions

The implementation of PHT represents a significant advance in pediatric heart care. Domino and split-root techniques within the PHT framework have the potential to substantially increase both donor availability and recipient capacity. These strategies usher in a new era of organ stewardship through addressing the challenge of donor organ shortage.

Options for pediatric heart valve replacement

Heart valve replacement is indicated for children with irreparable heart valve disease. These replacements come in a variety of forms including mechanical, xenograft tissue, allograft tissue, and autograft tissue valves. These options each have unique benefits and risks profiles. Mechanical valves are the most structurally durable; however, they represent significant thrombogenic risks and require anticoagulant therapy. Xenograft and homograft tissue valves do not carry the thrombogenic risks found with mechanical valves but also do not have the structural integrity of mechanical valves. Importantly, neither of these options allows for the somatic growth, requiring serial reoperation to implant upsized valves. Autograft implantation and partial heart transplantation each allow for the implantation of growing valves; however, autografts require for either a mechanical or bioprosthetic valve to be fitted into another valve position and PHT requires immunosuppressive medication to allow for the growth of the valve. In summary, outcomes of valve implantation in the pediatric population are significantly subpar compared to the outcomes enjoyed by the adult population. To remedy this, further innovation is needed in heart valve replacement technology.

Organizational challenges for partial heart transplantation

Partial heart transplantation (PHT) has emerged as a new treatment strategy to correct unrepairable heart valve dysfunction in pediatric patients. PHT selectively replaces the dysfunctional components of the recipient's heart and spares the native ventricles. As a result, the transplant biology of PHTs differs from heart transplants. Notably, donor hearts that are unsuitable for whole heart transplantation can be used, graft preservation can be prolonged and immunosuppression levels can be lowered. These nuances of PHT transplant biology have important implications for organizational aspects of PHT clinical application.

Storage, preservation, and rehabilitation of living heart valves to treat congenital heart disease

Heart valve disease patients undergo multiple surgeries to replace structurally degraded valve prostheses, highlighting the need for valve replacements with growth and self-repair capacity. Given allogeneic valve transplantation's promise in meeting these goals by delivering a living valve replacement, we propose a framework for preserving and rehabilitating living valves ex vivo.

Partial heart transplantation for destructive infective endocarditis

Infective endocarditis frequently spreads beyond the valve tissue, especially in the aortic location. Invasive endocarditis may lead to abscess formation or fistula, with substantial tissue loss. Here, the case of a 31-year-old male patient with destructive aortic and pulmonary valve endocarditis and a subaortic mural defect who underwent patch closure of the ventricular septal defect and aortic and pulmonary root replacement and right coronary artery bypass graft is presented. This is an uncommon condition and stress is placed on imaging of the technical aspects of the case.

Aortic Valve Embryology, Mechanobiology, and Second Messenger Pathways: Implications for Clinical Practice

During the Renaissance, Leonardo Da Vinci was the first person to successfully detail the anatomy of the aortic root and its adjacent structures. Ever since, novel insights into morphology, function, and their interplay have accumulated, resulting in advanced knowledge on the complex functional characteristics of the aortic valve (AV) and root. This has shifted our vision from the AV as being a static structure towards that of a dynamic interconnected apparatus within the aortic root as a functional unit, exhibiting a complex interplay with adjacent structures via both humoral and mechanical stimuli. This paradigm shift has stimulated surgical treatment strategies of valvular disease that seek to recapitulate healthy AV function, whereby AV disease can no longer be seen as an isolated morphological pathology which needs to be replaced. As prostheses still cannot reproduce the complexity of human nature, treatment of diseased AVs, whether stenotic or insufficient, has tremendously evolved, with a similar shift towards treatments options that are more hemodynamically centered, such as the Ross procedure and valve-conserving surgery. Native AV and root components allow for an efficient Venturi effect over the valve to allow for optimal opening during the cardiac cycle, while also alleviating the left ventricle. Next to that, several receptors are present on native AV leaflets, enabling messenger pathways based on their interaction with blood and other shear-stress-related stimuli. Many of these physiological and hemodynamical processes are under-acknowledged but may hold important clues for innovative treatment strategies, or as potential novel targets for therapeutic agents that halt or reverse the process of valve degeneration. A structured overview of these pathways and their implications for cardiothoracic surgeons and cardiologists is lacking. As such, we provide an overview on embryology, hemodynamics, and messenger pathways of the healthy and diseased AV and its implications for clinical practice, by relating this knowledge to current treatment alternatives and clinical decision making.

Partial Heart Transplantation - How to Change the System

Partial heart transplantation is the first clinically successful approach to deliver growing heart valve implants. To date, 13 clinical partial heart transplants have been performed. However, turning partial heart transplantation into a routine procedure that is available to all children who would benefit from growing heart valve implants poses formidable logistical challenges. Firstly, a supply for partial heart transplant donor grafts needs to be developed. This challenge is complicated by the scarcity of donor organs. Importantly, the donor pools for orthotopic heart transplants, partial heart transplants and cadaver homografts overlap. Secondly, partial heart transplants need to be allocated. Factors relevant for equitable allocation include the indication, anatomical fit, recipient clinical status and time on the wait list. Finally, partial heart transplantation will require regulation and oversight, which only recently has been undertaken by the Food and Drug Administration, which regulates human cellular and tissue-based products. Overcoming these challenges will require a change in the system. Once this is achieved, partial heart transplantation could open new horizons for children who require growing tissue implants.

Surgical Heritage: You Had to Be There, Ross: The Comeback Kid

Half a century after the first pulmonary autograft operation (Ross operation), performed in 1967 by Donald Ross in central London, there is a very strong conviction that the Ross operation is the best available valve substitute today, not only for children, but also for younger and older adults. The Ross operation has stimulated a lot of science to do with tissue-engineering and biology of heart valves, which is a promising avenue for the future. For one of us (M.Y.), it has certainly been a privilege to be associated with the comeback of the Ross operation.

Bioinspired polymeric heart valves: A combined in vitro and in silico approach

Background

Polymeric heart valves (PHVs) may address the limitations of mechanical and tissue valves in the treatment of valvular heart disease. In this study, a bioinspired valve was designed, assessed in silico, and validated by an in vitro model to develop a valve with optimum function for pediatric applications.

Methods

A bioinspired heart valve was created computationally with leaflet curvature derived from native valve anatomies. A valve diameter of 18 mm was chosen to approach sizes suitable for younger patients. Valves of different thicknesses were fabricated via dip-coating with siloxane-based polyurethane and tested in a pulse duplicator for their hydrodynamic function. The same valves were tested computationally using an arbitrary Lagrangian-Eulerian plus immersed solid approach, in which the fluid-structure interaction between the valves and fluid passing through them was studied and compared with experimental data.

Results

Computational analysis showed that valves of 110 to 200 μm thickness had effective orifice areas (EOAs) of 1.20 to 1.30 cm2, with thinner valves exhibiting larger openings. In vitro tests demonstrated that PHVs of similar thickness had EOAs of 1.05 to 1.35 cm2 and regurgitant fractions (RFs) <7%. Valves with thinner leaflets exhibited optimal systolic performance, whereas thicker valves had lower RFs.

Conclusions

Bioinspired PHVs demonstrated good hydrodynamic performance that exceeded ISO 5840-2 standards. Both methods of analysis showed similar correlations between leaflet thickness and valve systolic function. Further development of this PHV may lead to enhanced durability and thus a more reliable heart valve replacement than contemporary options.

Trends in pediatric donor heart discard rates and the potential use of unallocated hearts for allogeneic valve transplantation

Objectives

Allogeneic valve transplantation is an emerging therapy that delivers a living valve from a donor heart. We reviewed the national discard rate of pediatric and young adult (aged 25 years or younger) donor grafts to estimate the number of hearts potentially available to source valve allotransplantation.

Methods

We queried the United Network for Organ Sharing database to identify pediatric and young adult heart donors from 1987 to 2022. Donor heart discard was defined as nontransplantation of the allograft.

Results

Of 72,460 pediatric/young adult heart donations, 41,065 (56.7%) were transplanted and 31,395 (43.3%) were unutilized. The average annual number of discarded hearts in era 1 (1987-2000), era 2 (2000-2010), and era 3 (2010-2022) was 791 (42.8%), 1035 (46.3%), and 843 (41.2%), respectively. From 2017 to 2021, the average annual number of discards by age was: 39 (31.8%) neonates/infants, 78 (38.0%) toddlers, 41 (49.4%) young children, 240 (38.0%) adolescents, and 498 (40.1%) young adults. High-volume procurement regions had the greatest proportion of nonutilization, with the national average discard rate ranging from 39% to 49%. The most frequently documented reasons for nonallocation were distribution to the heart valve industry (26.5%), presumably due to suboptimal graft function, poor organ function (22.7%), and logistical challenges (10.8%).

Conclusions

With ∼900 pediatric/young adult donor hearts discarded annually, unutilized grafts represent a potential source of valves for allogeneic valve transplant to supplement current conduit and valve replacement surgery. The limited availability of neonatal and infant hearts may limit this technique in the youngest patients, for whom cryopreserved homografts or xenografts will likely remain the primary valve substitute.

Scientific Evolution of Artificial Heart Valves: A Narrative Review

Cardiovascular disorders have always been the top contributors to the number of mortality occurring worldwide. But the last few decades have seen a drop in those numbers as the lives of millions of people have been saved due to ground-breaking advances in both therapeutic and surgical treatment modalities. Achieving this level of scientific glory in cardiology was a challenging feat. The credit goes to the scientists and physicians of the previous century who, despite their time's technological limitations, made discoveries and laid a solid foundation for modern medicine. Valvular complications are a major part of the global burden of cardiac diseases. The ongoing development of heart valve replacements remains a fascinating subject, as it continues to progress. Valve replacements comprise either mechanical heart valves or bioprosthetic heart valves. Both types of valves have their merits and demerits; their usage depends mostly on individual patient requirements. This article aims to review the evolution of the implantation of heart valves, and it is the objective of this article to give credit to scientists and physicians for their contributions. The article highlights the research gaps in finding more durable materials and the scope of further research in creating a heart valve that can be universally used for better patient outcomes.

Partial heart transplantation for pediatric heart valve dysfunction: A clinical trial protocol

Congenital heart defects are the most common type of birth defects in humans and frequently involve heart valve dysfunction. The current treatment for unrepairable heart valves involves valve replacement with an implant, Ross pulmonary autotransplantation, or conventional orthotopic heart transplantation. Although these treatments are appropriate for older children and adults, they do not result in the same efficacy and durability in infants and young children for several reasons. Heart valve implants do not grow with the. Ross pulmonary autotransplants have a high mortality rate in neonates and are not feasible if the pulmonary valve is dysfunctional or absent. Furthermore, orthotopic heart transplants invariably fail from ventricular dysfunction over time. Therefore, the treatment of irreparable heart valves in infants and young children remains an unsolved problem. The objective of this single-arm, prospective study is to offer an alternative solution based on a new type of transplant, which we call "partial heart transplantation." Partial heart transplantation differs from conventional orthotopic heart transplantation because only the part of the heart containing the heart valve is transplanted. Similar to Ross pulmonary autotransplants and conventional orthotopic heart transplants, partial heart transplants contain live cells that should allow it to grow with the recipient child. Therefore, partial heart transplants will require immunosuppression. The risks from immunosuppression can be managed, as seen in conventional orthotopic heart transplant recipients. Stopping immunosuppression will simply turn the growing partial heart transplant into a non-growing homovital homograft. Once this homograft deteriorates, it can be replaced with a durable adult-sized mechanical implant. The protocol for our single-arm trial is described. The ClinicalTrials.gov trial registration number is NCT05372757.

A New Detergent for the Effective Decellularization of Bovine and Porcine Pericardia

Human and animal pericardia are among the most widely exploited materials suitable to repair damaged tissues in the cardiovascular surgery context. Autologous, xenogeneic (chemically treated) and homologous pericardia are largely utilized, but they do exhibit some crucial drawbacks. Any tissue treated with glutaraldehyde is known to be prone to calcification in vivo, lacks regeneration potential, has limited durability, and can result in cytotoxicity. Moreover, autologous tissues have limited availability. Decellularized biological tissues represent a promising alternative: decellularization removes cellular and nuclear components from native tissues and makes them suitable for repopulation by autologous cells upon implantation into the body. The present work aims to assess the effects of a new detergent, i.e., Tergitol, for decellularizing bovine and porcine pericardia. The decellularization procedure successfully removed cells, while preserving the histoarchitecture of the extracellular matrix. No cytotoxic effect was observed. Therefore, decellularized pericardia showed potential to be used as scaffold for cardiovascular tissue regeneration.

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.

Long-term survival after xenograft versus homograft aortic root replacement: Results from a prospective randomized trial

OBJECTIVE

The study objective was to investigate the long-term survival of patients undergoing xenograft versus homograft full root aortic valve replacement.

METHODS

A total of 166 patients requiring aortic valve surgery were randomized to undergo the Freestyle (Medtronic Inc, Minneapolis, Minn) bioprosthesis (N = 90) or a homograft (N = 76) full root aortic valve replacement between 1997 and 2005 in a single institution. Six patients randomly assigned to the homograft crossed over to the Freestyle bioprosthesis because of the unavailability of suitably sized homografts. All surgeons were required to adhere to the standard surgical technique for homograft root implantation previously described. Follow-up was 98.5% complete.

RESULTS

The mean age of the study population was 65 ± 8 years. Coronary artery bypass grafting was associated with root aortic valve replacement in 76 of 166 patients (46%, P = not significant between groups), and overall hospital mortality was 4.8% (8/166, P = not significant between groups). Median follow-up was 13.8 years (range, 0-21.8 years; 2033 patient-years). The Kaplan-Meier survival analysis showed that there was no significant difference in overall survival between the 2 arms at 5, 10, and 15 years. Twenty-year survival was 28.3% ± 5% for the Freestyle group versus 25.1% ± 5.7% for the homograft group (P = .90), which was comparable to the age- and sex-matched UK general population. The freedom from aortic valve reoperation at 20 years was comparable for the Freestyle group versus the homograft group (67.9% ± 8.8% vs 67.2% ± 10.3%, respectively; P = .74).

CONCLUSIONS

This is the first study to investigate the long-term survival of xenograft versus homograft full root aortic valve replacement from a prospective randomized trial. The observed 20-year overall survival and freedom from aortic valve reoperation serve as a benchmark for future studies on interventions for aortic valve disease in the elderly.

Revisiting the guidelines and choice the ideal substitute for aortic valve endocarditis

Aortic valve replacement is the most commonly performed cardiac surgical operation worldwide for infective endocarditis (IE). Long-term durability and avoidance of infection relapse are the treatment goals. However, no detailed guidelines on prosthesis selection and surgical strategy are available. Management should be guided by a comprehensive evaluation of infection extension and its microbiological characteristics, the clinical profile of the patient and the risk of infection recurrence. We conducted a literature search of the PubMed database, EMBASE and Cochrane Library (through November 2019) for studies reporting to the use of biological substitutes in aortic valve endocarditis (AVE). Studies comparing long-term outcomes in the use of allogenic and autologous with conventional prostheses were investigated. Conventional mechanical or stented xenografts are the preferred choice for localized aortic infection. In cases of complex IE with the involvement of the root or the aorto-mitral continuity, the use of homografts are recommended, according to surgeon's and center experience. Homograft use needs to be balanced against the risk of structural degeneration. Prosthetic bioroot or prosthetic valved conduit with a mechanical or bioprosthetic valve are acceptable alternatives. The choice of aortic valves substitute and surgical strategy in IE is multifaceted. Principles guiding the selection of prosthesis and surgical approach rely on the long-term durability and the avoidance of infection relapse. A decisional algorithm considering the extension of the infection and its microbiological characteristics, the clinical profile of the patient and the risk of infection recurrence is provided. A multidisciplinary effort is required to achieve consistent outcomes.

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.

Ectopic mineralization in heart valves: new insights from in vivo and in vitro procalcific models and promising perspectives on noncalcifiable bioengineered valves

Ectopic calcification of native and bioprosthetic heart valves represents a major public health problem causing severe morbidity and mortality worldwide. Valve procalcific degeneration is known to be caused mainly by calcium salt precipitation onto membranes of suffering non-scavenged cells and dead-cell-derived products acting as major hydroxyapatite nucleators. Although etiopathogenesis of calcification in native valves is still far from being exhaustively elucidated, it is well known that bioprosthesis mineralization may be primed by glutaraldehyde-mediated toxicity for xenografts, cryopreservation-related damage for allografts and graft immune rejection for both. Instead, mechanical valves, which are free from calcification, are extremely thrombogenic, requiring chronic anticoagulation therapies for transplanted patients. Since surgical substitution of failed valves is still the leading therapeutic option, progressive improvements in tissue engineering techniques are crucial to attain readily available valve implants with good biocompatibility, proper functionality and long-term durability in order to meet the considerable clinical demand for valve substitutes. Bioengineered valves obtained from acellular non-valvular scaffolds or decellularized native valves are proving to be a compelling alternative to mechanical and bioprosthetic valve implants, as they appear to permit repopulation by the host's own cells with associated tissue remodelling, growth and repair, besides showing less propensity to calcification and adequate hemodynamic performances. In this review, insights into valve calcification onset as revealed by in vivo and in vitro procalcific models are updated as well as advances in the field of valve bioengineering.

Mechanical and structural properties of human aortic and pulmonary allografts do not deteriorate in the first 10 years of cryopreservation and storage in nitrogen

The aortic and pulmonary allograft heart valves (AHV) are used in the cardiac surgery for replacing the impaired semilunar valves. They are harvested from donor hearts and cryostored in tissue banks. The expiration period was set to 5 years arbitrarily. We hypothesized that their mechanical and structural properties do not deteriorate after this period. A total of 64 human AHV (31 aortic and 33 pulmonary) of different length of cryopreservation (fresh, 0-5, 5-10, over 10 years) were sampled to different tissue strips (artery, leaflet, ventriculo-arterial junction) and tested by tensile test with loading velocity 10 mm/min until tissue rupture. Neighbouring regions of tissue were processed histologically and evaluated for elastin and collagen area fraction. The results were evaluated statistically. In aortic AHV, the physical deformation response of wall samples to stress did not changed significantly neither during the process of cryopreservation nor during the first 10 years of storage. In pulmonary AHV, the ultimate strain dropped after 5 years of cryopreservation indicating that pulmonary artery was significantly less deformable at the time of rupture. On the other hand, the ultimate stress was equal during the first 10 years of cryostorage. The changes in collagen and elastin amount in the tissue samples were not associated with mechanical impairment. Neither elasticity, stiffness and solidity nor morphology of aortic and pulmonary AHV did not change reasonably with cryopreservation and in the first 10 years of cryostorage. This evidence suggests that the expiration period might be extended in the future.

Cadaver donation: structural integrity of pulmonary homografts harvested 48 h post mortem in the juvenile ovine model

Cryopreserved pulmonary homograft (CPH) implantation remains the gold standard for reconstruction of the right ventricular outflow tract (RVOT). Harvesting homografts < 24-h post mortem is the international norm, thereby largely excluding cadaveric donors. This study examines the structural integrity and stability of ovine pulmonary homografts harvested after a 48-h post mortem period, cryopreserved and then implanted for up to 180 days. Fifteen ovine pulmonary homografts were harvested 48-h post mortem and cryopreserved. Five CPH served as a control group (group 1; n = 5). CPH were implanted in the RVOT of juvenile sheep and explanted after 14 days (group 2; n = 5) and 180 days (group 3; n = 5). Leaflet integrity was evaluated by strength analysis, using tensile strength (TS), Young's modulus (YM) and thermal denaturation temperature (T_d), and morphology, including haematoxylin and eosin (H&E), Picrosirius red staining, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and von Kossa stains. Echocardiography confirmed normal function in all implants. In explants, no reduction in TS, YM or T_d could be demonstrated and H&E showed mostly acellular leaflet tissue with no difference on Picrosirius red. TEM demonstrated consistent collagen disruption after cryopreservation in all three groups, with no morphological deterioration during the study period. von Kossa stains showed mild calcification in group 3. No deterioration of structural integrity could be demonstrated using strength or morphological evaluations between the controls and implant groups over the study period. Extending the post mortem harvesting time of homografts beyond 24 h did not appear to negatively affect the long-term performance of such transplanted valves in this study.

Recurrent Hemorrhagic Conversion of Ischemic Stroke in a Patient with Mechanical Heart Valve: A Case Report and Literature Review

The authors present a unique case of recurrent stroke, discovered to be secondary to hemorrhagic conversion of microemboli from a mechanical aortic valve despite anticoagulation with Coumadin. The complexity of this case was magnified by the patient’s young age, a mechanical heart valve (MHV), and a need for anticoagulation to maintain MHV patency in a setting of potentially life-threatening intracranial hemorrhage. Anticoagulant and antiplatelet therapy are risk factors for hemorrhagic conversion post-cerebral ischemia; however, the pathophysiology underlying endothelial cell dysfunction causing red blood cell extravasation is an active area of basic and clinical research. The need for randomized clinical trials to aid in the creation of standardized treatment protocol continues to go unmet. Consequently, there is marked variation in therapeutic approaches to treating intracranial hemorrhage in patients with an MHV. Unfortunately, patients with an MHV are considered at high thromboembolic (TE) risk, and these patients are often excluded from clinical trials of acute stroke due to their increased TE potential. The authors feel this case represents an example of endothelial dysfunction secondary to microthrombotic events originating from an MHV, which caused ischemic stroke with hemorrhagic conversion complicated by the need for anticoagulation for an MHV. This case offers a definitive treatment algorithm for a complex clinical dilemma.

Full-root Aortic Valve Replacement by Stentless Aortic Xenografts in Patients with Small Aortic Roots

In patients with small aortic roots who need an aortic valve replacement with biological valve substitutes, the implantation of the stented pericardial valve might not meet the functional needs. The implantation of a too-small stented pericardial valve, leading to an effective orifice area indexed to a body surface area less than 0.85 cm²/m², is regarded as prosthesis-patient mismatch (PPM). A PPM negatively affects the regression of left ventricular hypertrophy and thus the normalization of left ventricular function and the alleviation of symptoms. Persistent left ventricular hypertrophy is associated with an increased risk of arrhythmias and sudden cardiac death. In the case of predictable PPM, there are three options: 1) accept the PPM resulting from the implantation of a stented pericardial valve when comorbidities of the patient forbid the more technically demanding operative technique of implanting a larger prosthesis, 2) enlarge the aortic root to accommodate a larger stented valve substitute, or 3) implant a stentless biological valve or a homograft. Compared to classical aortic valve replacement with stented pericardial valves, the full-root implantation of stentless aortic xenografts offers the possibility of implanting a 3-4 mm larger valve in a given patient, thus allowing significant reduction in transvalvular gradients. However, a number of cardiac surgeons are reluctant to transform a classical aortic valve replacement with stented pericardial valves into the more technically challenging full-root implantation of stentless aortic xenografts. Given the potential hemodynamic advantages of stentless aortic xenografts, we have adopted full-root implantation to avoid PPM in patients with small aortic roots necessitating an aortic valve replacement. Here, we describe in detail a technique for the full-root implantation of stentless aortic xenografts, with emphasis on the management of the proximal suture line and coronary anastomoses. Limitations of this technique and alternative options are discussed.

Early Experience with Homograft Valve Banking

Homograft cardiac valves have been shown to have several advantages over conventional prosthetic valves. From October 1993 through November 1996, 273 homografts (262 valved and 11 non-valved) were used in various procedures at the All India Institute of Medical Sciences, New Delhi, India. The recommendations of the American Association of Tissue Banks were followed for procurement, harvesting, and storage of the valves. One hundred and ninety-six hearts were procured yielding a total of 439 homograft valves; 192 were pulmonary homografts, 187 were aortic homografts, and 60 were mitral homografts. Eighty-five homografts were used in the Ross procedure, 64 were used in homograft replacement of the aortic valve, 28 were used in replacement of the mitral valve, 85 were used in various operations for heart disease as valved conduits, and 11 homografts were used as either non-valved conduits or for patch repair. One hundred and thirty-five homografts (31%) were discarded for various reasons. Our early experience of valve banking is discussed.

Heart valve tissue engineering: how far is the bedside from the bench?

Heart disease, including valve pathologies, is the leading cause of death worldwide. Despite the progress made thanks to improving transplantation techniques, a perfect valve substitute has not yet been developed: once a diseased valve is replaced with current technologies, the newly implanted valve still needs to be changed some time in the future. This situation is particularly dramatic in the case of children and young adults, because of the necessity of valve growth during the patient's life. Our review focuses on the current status of heart valve (HV) therapy and the challenges that must be solved in the development of new approaches based on tissue engineering. Scientists and physicians have proposed tissue-engineered heart valves (TEHVs) as the most promising solution for HV replacement, especially given that they can help to avoid thrombosis, structural deterioration and xenoinfections. Lastly, TEHVs might also serve as a model for studying human valve development and pathologies.

One-year results from cryopreserved mitral allograft transplantation into the tricuspid position in a sheep experimental model

Mitral allografts are still used only exceptionally in the mitral or tricuspid position. The main indication remains infectious endocarditis of atrioventricular valves for its flexibility and low risk of infection. The aim of our study was to evaluate 1-year results of mitral allografts transplantation into the tricuspid position in a sheep model. Mitral allografts were processed, cryopreserved, and transplanted into the tricuspid position anatomically (Group I - 11 animals) or antianatomically (Group II - 8 animals). All survivors (4 from Group I, and 3 from Group II) were checked at 3, 6, and 12 months by echocardiography with the exception of one survivor from Group II (which was examinated only visually). Examination throughout follow-up included for mitral allograft regurgitation and annuli dilatation. At postmortem, the papillary muscles were healed and firmly anchored to the right ventricular wall in all subjects. Transventricular fixation of the papillary muscles with buttressed sutures was proven to be a stable, reproducible, and safe method for anchoring mitral allograft leaflets. There were no significant differences between the two implantation methods. Annulus support of mitral allografts might be very useful in this type of operation and could prevent annular dilatation.

Surgical management of destructive aortic endocarditis: left ventricular outflow reconstruction with the Sorin Pericarbon Freedom stentless bioprosthesis†

OBJECTIVES

The treatment of complicated aortic endocarditis with periannular abscesses and root disarrangement is a surgical challenge, and includes left ventricular outflow tract (LVOT) reconstruction with the patch technique or homograft implantation. The results of a simplified technique to reconstruct the LVOT in destructive endocarditis of either the aortic native valve or valve prosthesis with the Sorin Pericarbon Freedom stentless valve are reported.

METHODS

Since August 2007, 40 patients with destructive endocarditis (mean age: 69 ± 12, 75% males, European System for Cardiac Operative Risk Evaluation II (EuroSCORE II): 19 ± 13, New York Heart Association (NYHA) class: ≥3 in all cases) have undergone LVOT reconstruction with a Sorin Pericarbon Freedom stentless bioprosthesis. Seven patients (17.5%) were in septic or cardiogenic shock preoperatively, and 18 patients (45%) suffered from moderate or severe aortic regurgitation. Eleven patients (27.5%) experienced preoperative systemic embolizations. Thirty-six cases (90%) were valve redos and 9 patients (22.5%) had concomitant procedures. The mean follow-up was 26 ± 25 months.

RESULTS

One patient (2.5%) died early (<30 days) and another 3 patients never discharged died due to multiorgan failure and septic shock. Actuarial survival rate was 85 ± 6% at 1 year, and 76 ± 8% at 3 and 5 years, respectively. Twelve patients (30%) required pacemaker implantation because of atrioventricular block and 20 patients (50%) developed or showed a progression of renal failure. One patient (2.5%) had an endocarditis relapse, and 1 (2.5%) showed a mild paraprosthetic aortic leak. No patient needed reoperation. At the last echocardiographic evaluation, mean gradient, peak gradient and left ventricular ejection fraction were 7.9 ± 5.0 mmHg, 15.1 ± 7.2 mmHg and 63.3 ± 9.3%, respectively.

CONCLUSIONS

The Sorin Pericarbon Freedom stentless prosthesis, with the modified technique herein described, seems to be a good option in most of cases of destructive aortic valve endocarditis. It is promptly available in different sizes, easy to implant and, due to its pericardial inflow skirt, ideal for extensive reconstruction of the LVOT with good haemodynamic performance and low risk of relapse.

Durability of homografts used to treat complex aortic valve endocarditis

BACKGROUND

Acute bacterial endocarditis may be extremely destructive for cardiac valves and their periannular structures. It has been suggested that complex reconstruction procedures require the use of homografts because of their versatility and potency to resist repeated infection.

METHODS

We studied the long-term results of 69 patients with complex endocarditis who received homografts in the aortic position.

RESULTS

The results after a mean follow-up of 8.1 ± 5.1 years (median, 8.0 years) showed that the recurrence of endocarditis even in these complex cases is low (7%), but the incidence of structural valve degeneration (SVD) is high. Freedom from SVD at 10 years is only 60.0%. When aortic homografts degenerate, they predominantly calcify.

CONCLUSIONS

The use of homografts to reconstruct endocarditis-related aortic valve destruction is associated with a low recurrence of endocarditis but a high incidence of SVD in the long run.

In-vivo assessment of the morphology and hemodynamic functions of the BioValsalva™ composite valve-conduit graft using cardiac magnetic resonance imaging and computational modelling technology

BACKGROUND

The evaluation of any new cardiac valvular prosthesis should go beyond the classical morbidity and mortality rates and involve hemodynamic assessment. As a proof of concept, the objective of this study was to characterise for the first time the hemodynamics and the blood flow profiles at the aortic root in patients implanted with BioValsalva™ composite valve-conduit using comprehensive MRI and computer technologies.

METHODS

Four male patients implanted with BioValsalva™ and 2 age-matched normal controls (NC) underwent cardiac magnetic resonance imaging (MRI). Phase-contrast imaging with velocity-mapping in 3 orthogonal directions was performed at the level of the aortic root and descending thoracic aorta. Computational fluid dynamic (CFD) simulations were performed for all the subjects with patient-specific flow information derived from phase-contrast MR data.

RESULTS

The maximum and mean flow rates throughout the cardiac cycle at the aortic root level were very comparable between NC and BioValsalva™ patients (541 ± 199 vs. 567 ± 75 ml/s) and (95 ± 46 vs. 96 ± 10 ml/s), respectively. The maximum velocity (cm/s) was higher in patients (314 ± 49 vs. 223 ± 20; P = 0.06) due to relatively smaller effective orifice area (EOA), 2.99 ± 0.47 vs. 4.40 ± 0.24 cm2 (P = 0.06), however, the BioValsalva™ EOA was comparable to other reported prosthesis. The cross-sectional area and maximum diameter at the root were comparable between the two groups. BioValsalva™ conduit was stiffer than the native aortic wall, compliance (mm2 • mmHg(-1) • 10(-3)) values were (12.6 ± 4.2 vs 25.3 ± 0.4.; P = 0.06). The maximum time-averaged wall shear stress (Pa), at the ascending aorta was equivalent between the two groups, 17.17 ± 2.7 (NC) vs. 17.33 ± 4.7 (BioValsalva™ ). Flow streamlines at the root and ascending aorta were also similar between the two groups apart from a degree of helical flow that occurs at the outer curvature at the angle developed near the suture line.

CONCLUSIONS

BioValsalva™ composite valve-conduit prosthesis is potentially comparable to native aortic root in structural design and in many hemodynamic parameters, although it is stiffer. Surgeons should pay more attention to the surgical technique to maximise the reestablishment of normal smooth aortic curvature geometry to prevent unfavourable flow characteristics.

In vitro generation of atrioventricular heart valve neoscaffolds

Tissue engineering of cardiovascular structures represents a novel approach to improve clinical strategies in heart valve disease treatment. The aim of this study was to engineer decellularized atrioventricular heart valve neoscaffolds with an intact ultrastructure and to reseed them with umbilical cord-derived endothelial cells under physiological conditions in a bioreactor environment. Mitral (n=38) and tricuspid (n=36) valves were harvested from 40 hearts of German Landrace swine from a selected abattoir. Decellularization of atrioventricular heart valves was achieved by a detergent-based cell extraction protocol. Evaluation of the decellularization method was conducted with light microscopy and quantitative analysis of collagen and elastin content. The presence of residual DNA within the decellularized atrioventricular heart valves was determined with spectrophotometric quantification. The described decellularization regime produced full removal of native cells while maintaining the mechanical stability and the quantitative composition of the atrioventricular heart valve neoscaffolds. The surface of the xenogeneic matrix could be successfully reseeded with in vitro-expanded human umbilical cord-derived endothelial cells under physiological flow conditions. After complete decellularization with the detergent-based protocol described here, physiological reseeding of the xenogeneic neoscaffolds resulted in the formation of a confluent layer of human umbilical cord-derived endothelial cells. These results warrant further research toward the generation of atrioventricular heart valve neoscaffolds on the basis of decellularized xenogeneic tissue.

Homografts: a review

Since their introduction into clinical practice in 1965 homografts have become established in clinical routine. The storing and sterilization procedures have been improved over time. Long-term results showed that homografts had a superior durability compared to xenogenic biological prostheses. Approximately 40% were still in place 20 years after implantation in aortic position. Their low rate of thromboembolic events made a life-time anticoagulative therapy unnecessary and their hemodynamics were superior to all other heart valve prostheses. There exist two implantation techniques, subcoronary or mini-root, both technically more demanding compared with implantation of stented valve prostheses. When using the subcoronary technique, the valve is suspended into the aortic root leaving the coronary arteries untouched. The success of this technique, however, depends on the relation of the recipients aortic root and the implanted valve. The mini-root technique requires reimplantation of the coronary arteries but left the morphology of the valve and its root unchanged. Especially in patients with endocarditis, the mini-root technique offered the advantage of allowing for excision of all affected tissue with subsequent replacement by the homograft. The Ross-procedure uses the patient's own pulmonary valve as aortic valve substitute with implantation of a homograft in pulmonary position. This proved to be advantageous in children, since in these patients the degeneration of an aortic homograft was faster compared to an older population. This was explained by the recipient's immunologic response to the graft which was more pronounced in younger patients. The advantages of homografts with regards to hemodynamics and thromboembolic risk make them a good alternative to mechanical prostheses in younger, active patients. In very young patients, a Ross-procedure was shown to be superior to aortic homografts due to slower degeneration of the autograft. The decision to use a homograft must be made individually according to the patients demands.

Long-term clinical outcomes after aortic valve replacement using cryopreserved aortic allograft

BACKGROUND

Although the frequency of biological valve use in treating aortic valve disease is increasing, the critical limiting factor, "structural deterioration," remains unresolved. Analysis of long-term outcomes after implantation of cryopreserved aortic allografts will yield further information related to the durability of the aortic allograft, possibly suggesting mechanisms underlying or strategies to prevent or treat the structural deterioration of biological valve substitutes.

METHODS

A total of 840 cryopreserved aortic allografts implanted in the last 35 years were reviewed with clinical follow-up completed in 99% of the consecutive series. By June 2010, 285 implanted allografts had been surgically explanted, 288 patients died before allograft removal, and 267 patients are under continued follow-up.

RESULTS

Cryopreserved aortic allografts were durable for more than 15 years in the middle-aged and older patient population. The estimated median time until structural deterioration was 20 years post-implantation, and 2 allografts have been functioning well for more than 30 years. Structural deterioration was independently related to the young age of the recipient, elderly age of the donor, severe obesity in the recipient, history of blood transfusion in the recipient, and full-root implantation technique. Infection of the implanted allograft necessitating reintervention rarely occurred. Reintervention for the allograft demonstrated 2% in-hospital mortality.

CONCLUSIONS

Cryopreserved aortic allografts were durable for more than 15 years. Structural deterioration of aortic allografts was related to multiple factors. The age of the recipient and the donor, obesity and blood transfusion history of the recipient, and implantation technique were identified as the most important factors contributing to allograft failure.

Orthotopic replacement of aortic heart valves with tissue-engineered grafts

AIMS

Heart valve tissue engineering aims to create a graft with improved durability compared to routinely used valve substitutes. This study presents the function and morphological changes of a tissue-engineered aortic valve (TEV) compared to the cryopreserved valve (CPV), aortic valve (AV) allografts in an orthotopic position in sheep.

METHODS AND RESULTS

Ovine AV conduits (n=5) were decellularized with detergents. Autologous endothelial cells (ECs) were seeded onto the valve surface and cultured under physiological conditions using a high pulsatile flow. Grafts were implanted as a root with reimplantation of coronary ostia in sheep. Crystalloid cardioplegia and isogenic blood transfusions from previous sacrificed sheep were used. Only antiplatelet aggregation therapy was used postoperatively. CPVs (n=4) served as controls. The grafts were investigated for function (echocardiography, magnetic resonance investigation), morpho/histological appearance, graft rejection, and calcification at 3 months. Decellularization led to cell-free scaffolds with preserved extracellular matrices, including the basement membrane. TEVs were covered with ECs expressing typical endothelial markers. Neither dilatation, stenosis, reductions of cusp mobility nor a significant transvalvular gradient, were observed in the TEV group. Explanted valves exhibited normal morphology without signs of inflammation. An endothelial monolayer covered cusps and the valve sinus. In the CPV group, sporadic, macroscopic, calcified degeneration with mild AV insufficiency was noted. Histology revealed signs of rejection and incipient calcification of the tissue.

CONCLUSION

Tissue-engineered AV based on decellularized valve allografts satisfy short-term requirements of the systemic circulation in sheep. Although results of long-term experiments are pending, the lack of degenerative traits thus far, makes these grafts a promising alternative for future aortic heart valve surgery.

Homografts in aortic position: does blood group incompatibility have an impact on patient outcomes?

OBJECTIVES

Aortic homografts are an alternative to mechanical or biological valve prostheses. Homografts are generally not transplanted ABO-compatible while this policy is still under debate. The purpose of this study was to investigate whether ABO compatibility impacts on long-term outcomes or not.

METHODS

Between 1992 and 2009, 363 adult patients with a mean age of 52 years received homografts in aortic position. Donor and acceptor blood groups could be obtained for 335 patients. Sixty-three percent received blood group-compatible (n = 212) (Group iso) and 37% non-blood group-compatible allografts (n = 123) (Group non-iso).

RESULTS

The overall event-free survival (freedom from death or reoperation) was 55.5% (n = 186). In the iso group, the event-free survival was 84.1% at 5 years and 63.3% at 10 years. In the non-iso group, the event-free survival was 79.4% at 5 years and 51.8% at 10 years. 28.5% of patients (n = 35) with ABO-incompatible and 25.5% (n = 54) with ABO-compatible grafts required reoperation. The mean time to reoperation in the iso group was 97.3 vs 90 months in the non-iso group.

CONCLUSIONS

In 17 years of research, we have not yet found a statistical significant difference in blood group incompatibility regarding overall event-free survival. In our opinion, there is no need to use ABO-compatible homografts for aortic valve replacement in adults. Histological and immunohistochemical assays are mandatory to confirm our results.

Use of fresh decellularized allografts for pulmonary valve replacement may reduce the reoperation rate in children and young adults: early report

BACKGROUND

Degeneration of xenografts or homografts is a major cause for reoperation in young patients after pulmonary valve replacement. We present the early results of fresh decellularized pulmonary homografts (DPH) implantation compared with glutaraldehyde-fixed bovine jugular vein (BJV) and cryopreserved homografts (CH).

METHODS AND RESULTS

Thirty-eight patients with DPH in pulmonary position were consecutively evaluated during the follow-up (up to 5 years) including medical examination, echocardiography, and MRI. These patients were matched according to age and pathology and compared with BJV (n=38) and CH (n=38) recipients. In contrast to BJV and CH groups, echocardiography revealed no increase of transvalvular gradient, cusp thickening, or aneurysmatic dilatation in DPH patients. Over time, DPH valve annulus diameters converge toward normal z-values. Five-year freedom from explantation was 100% for DPH and 86 ± 8% and 88 ± 7% for BJV and CH conduits, respectively. Additionally, MRI investigations in 17 DPH patients with follow-up time >2 years were compared with MRI data of 20 BJV recipients. Both patient groups (DPH and BJV) were at comparable ages (mean, 12.7 ± 6.1 versus 13.0 ± 3.0 years) and have comparable follow-up time (3.7 ± 1.0 versus 2.7 ± 0.9 years). In DPH patients, the mean transvalvular gradient was significantly (P=0.001) lower (11 mm Hg) compared with the BJV group (23.2 mm Hg). Regurgitation fraction was 14 ± 3% and 4 ± 5% in DPH and BJV groups, respectively. In 3 DPH recipients, moderate regurgitation was documented after surgery and remained unchanged in follow-up.

CONCLUSIONS

In contrast to conventional homografts and xenografts, decellularized fresh allograft valves showed improved freedom from explantation, provided low gradients in follow-up, and exhibited adaptive growth.

Pulmonary Homografts for Aortic Valve Replacement: Long-term Comparison with Aortic Grafts

<p><b>Objective:</b> The use of homografts for aortic valve replacement (AVR) is an alternative to mechanical or biological valve prostheses, especially in younger patients. This retrospective comparative study evaluated our single-center long-term results, with a focus on the different origins of the homografts.</p><p><b>Methods:</b> Since 1992, 366 adult patients have undergone AVR with homografts at our center. We compared 320 homografts of aortic origin and 46 homografts of pulmonary origin. The grafts were implanted via either a subcoronary technique or the root replacement technique. We performed a multivariate analysis to identify independent factors that influence survival. Freedom from reintervention and survival rates were calculated as cumulative events according to the Kaplan-Meier method, and differences were tested with the log-rank test.</p><p><b>Results:</b> Overall mortality within 1 year was 6.5% (21/320) in the aortic graft group and 17.4% (8/46) in the pulmonary graft group. In the pulmonary graft group, 4 patients died from valve-related complications, 1 patient died after additional heterotopic heart transplantation, and 1 patient who entered with a primary higher risk died from a prosthesis infection. Two patients died from non-valve-related causes. During the long-term follow-up, the 15-year survival rate was 79.9% for patients in the aortic graft group and 68.7% for patients in the pulmonary graft group (<i>P</i> = .049). The rate of freedom from reoperation was 77.7% in the aortic graft group and 57.4% in the pulmonary graft group (<i>P</i> < .001). The reasons for homograft explantation were graft infections (aortic graft group, 5.0%; pulmonary graft group, 6.5%) and degeneration (aortic graft group, 7.5%; pulmonary graft group, 32.6%).</p><p><b>Conclusion:</b> Our study demonstrated superior rates of survival and freedom from reintervention after AVR with aortic homografts. Implantation with a pulmonary graft was associated with a higher risk of redo surgery, owing to earlier degenerative alterations.</p>

Mid- to long-term outcomes of cardiovascular tissue replacements utilizing homografts harvested and stored at Japanese institutional tissue banks

PURPOSE

We reviewed our clinical experiences with cardiovascular homografts harvested and preserved at our institutional tissue banks.

METHODS

Since our bank was first established in Japan in 1990, 74 patients have undergone various surgical procedures using homografts. We classified them into five groups according to the procedure: Group I, subcoronary implantation of a homograft aortic valve; Group II, homograft aortic root replacement for active native or prosthetic endocarditis; Group III, homograft aortic replacement for mycotic aortic aneurysms or infected grafts; Group IV, pulmonary homografts in the Ross operation; and Group V, pulmonary homograft conduits for complex congenital heart diseases.

RESULTS

The 9- to 10-year survival rates were good and acceptable, respectively, for the patients in all five groups. The infection recurrence rate was low (8%). Cardiac event-free rates, including deaths, were 0.57 in Group I, 0.58 Group in II, 0.75 in Group III, 0.81 in Group IV, and 0.69 in Group V operations. The rates of structural homograft deterioration suggest that homografts deteriorate more rapidly after subcoronary implantation than aortic root replacements (P = 0.058).

CONCLUSIONS

Subcoronary implantation should probably be abandoned for routine aortic valve replacement, but the continued use of homografts will provide valuable alternatives for patients with active infectious cardiovascular diseases. For the Ross operation, pulmonary valve homografts showed good durability.