Clinical experience of reoperative right ventricular outflow tract reconstruction with valved conduits: risk factors for conduit failure in long-term follow-up

Reconstruction of right ventricular outflow tract in patients with congenital heart disease in various age groups remains a controversial issue. Currently, a little is known about the fate of secondary and subsequent conduit. The aim of the study was to determine risk factors of conduit failure, evaluate long-term conduit survival, find out which type of conduit should be preferred in case of reoperations. We performed a retrospective analysis of a total of 249 records of valved conduit secondary and subsequent replacement in right ventricular outflow tract in 197 patients. Median follow-up was 5.7 years. The study endpoints were defined as conduit explants; balloon dilatation of the graft (excluding balloon dilatation of left/right pulmonary artery), transcatheter pulmonary valve implantation; heart transplantation or death of the patient. There were total of 21 deaths (11% mortality) among 197 patients during the follow-up, 2 patients underwent heart transplant, in 23 implanted conduits pulmonary angioplasty or/including transcatheter pulmonary valve implantation was afterwards performed due to graft failure, conduit had to be explanted in 46 cases. After 28 years follow-up, freedom from graft failure after 5 years was 77%, 48% after 10 years and 21% after 15 years. Reoperative right ventricular outflow tract reconstruction demonstrates good mid-term and acceptable long-term outcomes regardless of the type of conduit implanted. Worse long-term graft survival of secondary and further conduits is associated with younger age of the recipient at implantation, small size of the conduit, younger age of donor and male donor in case of allograft implantation.

Heterotopically-placed right ventricle-to-pulmonary artery conduit does not negatively affect outcomes

OBJECTIVES

Since the introduction of surgical implantation of conduit for right ventricle-to-pulmonary artery pathway reconstruction, there has been a number of studies on possible factors which might potentially affect conduit longevity, as well as patient's reintervention-free and overall survival. Still, no definite consensual agreement could be made thus far. We aimed to compare conduit longevity, reintervention-free survival, and overall survival between patients with congenital heart diseases indicated for operations involving right ventricle-to-pulmonary artery pathway reconstruction whose conduits were placed heterotopically to those with orthotopically placed ones.

MATERIALS AND METHODS

We retrospectively collected data from electronic medical records of Ramathibodi hospital from 1st January 2005 to 31st December 2022. Patients with congenital heart diseases whose operations involved reconstruction of right ventricle-to-pulmonary artery continuity were included. Patients whose medical record data were significantly missing were excluded. Demographic data, operative, and postoperative details were collected and reviewed.

RESULTS

There were 67 patients included in our study, with 25 receiving orthotopic and the other 42 receiving heterotopic conduit implantation. Conduit dysfunction-free, reintervention-free, and overall survival were not statistically different between both groups. There was 1 early and no late death up to the end date of our study.

CONCLUSIONS

Conduits placed on a heterotopic position did not result in worse longevity, reintervention-free survival, as well as overall survival when compared to conduits placed on an orthotopic position. This suggested that the less technically demanding heterotopic conduit placement could be recommended as an operation of choice for right ventricular outflow tract reconstruction.

Current methods for fabricating 3D cardiac engineered constructs

3D cardiac engineered constructs have yielded not only the next generation of cardiac regenerative medicine but also have allowed for more accurate modeling of both healthy and diseased cardiac tissues. This is critical as current cardiac treatments are rudimentary and often default to eventual heart transplants. This review serves to highlight the various cell types found in cardiac tissues and how they correspond with current advanced fabrication methods for creating cardiac engineered constructs capable of shedding light on various pathologies and providing the therapeutic potential for damaged myocardium. In addition, insight is given toward the future direction of the field with an emphasis on the creation of specialized and personalized constructs that model the region-specific microtopography and function of native cardiac tissues.

Association between homograft tissue exposure and allosensitization prior to heart transplant in patients with congenital heart disease

BACKGROUND

Surgical repair for patients with congenital heart disease (CHD) often incorporates homograft tissue or other foreign material that can lead to allosensitization. We sought to identify the relationship between pre-sensitization prior to heart transplant and exposure to homograft tissue in CHD patients.

METHODS

Retrospective chart review of all CHD patients who underwent heart transplant at a major pediatric transplant center between 1/1/2011-3/31/18. Operative records determined use of homograft tissue or foreign material. Panel reactive antibody (PRA) and Luminex^TM single-antigen bead (SAB) testing results were reviewed. Statistical analysis determined odds of pre-sensitization in patients exposed to homograft tissue.

RESULTS

Fifty-six CHD patients underwent transplant during the review period. Thirteen patients (23%) were pre-sensitized by PRA>10%. By SAB testing, 33 patients (59%) developed any anti-HLA antibody >0 MFI, 30 patients (54%) >2000 MFI, and 19 patients (34%) >6000 MFI. Patients with homografts were more likely to be pre-sensitized by PRA (OR = 7.31, p = .007), and to have developed any anti-HLA antibody at various levels, >0 (OR = 4.52, p = .034), >2000 (OR = 8.59, p = .003), and >6000 (OR = 8.50, p = .004). Of patients with homografts, those pre-sensitized by PRA had longer exposure times (9.80 vs 4.96 years, p = .025). There was no difference in exposure time with relation to pre-sensitization by SAB testing.

CONCLUSIONS

Previous exposure to homograft tissue appears to increase the odds of pre-sensitization by either the PRA or SAB testing. Longer exposure time to homograft tissue prior to transplant is associated with increased pre-sensitization at transplant as determined by PRA, though not by SAB testing.

Repopulation of decellularised porcine pulmonary valves in the right ventricular outflow tract of sheep: Role of macrophages

The primary objective was to evaluate performance of low concentration SDS decellularised porcine pulmonary roots in the right ventricular outflow tract of juvenile sheep. Secondary objectives were to explore the cellular population of the roots over time. Animals were monitored by echocardiography and roots explanted at 1, 3, 6 (n = 4) and 12 months (n = 8) for gross analysis. Explanted roots were subject to histological, immunohistochemical and quantitative calcium analysis (n = 4 at 1, 3 and 12 months) and determination of material properties (n = 4; 12 months). Cryopreserved ovine pulmonary root allografts (n = 4) implanted for 12 months, and non-implanted cellular ovine roots were analysed for comparative purposes. Decellularised porcine pulmonary roots functioned well and were in very good condition with soft, thin and pliable leaflets. Morphometric analysis showed cellular population by 1 month. However, by 12 months the total number of cells was less than 50% of the total cells in non-implanted native ovine roots. Repopulation of the decellularised porcine tissues with stromal (α-SMA+; vimentin+) and progenitor cells (CD34+; CD271+) appeared to be orchestrated by macrophages (MAC 387+/ CD163low and CD163+/MAC 387-). The calcium content of the decellularised porcine pulmonary root tissues increased over the 12-month period but remained low (except suture points) at 401 ppm (wet weight) or below. The material properties of the decellularised porcine pulmonary root wall were unchanged compared to pre-implantation. There were some changes in the leaflets but importantly, the porcine tissues did not become stiffer. The decellularised porcine pulmonary roots showed good functional performance in vivo and were repopulated with ovine cells of the appropriate phenotype in a process orchestrated by M2 macrophages, highlighting the importance of these cells in the constructive tissue remodelling of cardiac root tissues.

Application of Homograft Valved Conduit in Cardiac Surgery

Valved conduits often correct the blood flow of congenital heart disease by connecting the right ventricle to the pulmonary artery (RV-PA). The homograft valved conduit was invented in the 1960s, but its wide application is limited due to the lack of effective sterilization and preservation methods. Modern cryopreservation prolongs the preservation time of homograft valved conduit, which makes it become the most important treatment at present, and is widely used in Ross and other operations. However, homograft valved conduit has limited biocompatibility and durability and lacks any additional growth capacity. Therefore, decellularized valved conduit has been proposed as an effective improved method, which can reduce immune response and calcification, and has potential growth ability. In addition, as a possible substitute, commercial xenograft valved conduit has certain advantages in clinical application, and tissue engineering artificial valved conduit needs to be further studied.

The Ross procedure in children: a systematic review

Background

The Ross procedure involves autograft transplantation of the native pulmonary valve into the aortic position and reconstruction of the right ventricular outflow tract (RVOT) with a homograft. The operation offers the advantages of a native valve with excellent hemodynamic performance, the avoidance of anticoagulation, and growth potential. Conversely, the operation is technically demanding and imposes the risk of turning single-valve disease into double-valve disease. This systematic review reports outcomes of pediatric patients undergoing the Ross procedure.

Methods

An electronic search identified studies reporting outcomes on pediatric patients (mean age <18 years, max age <21 years) undergoing the Ross procedure. Long-term outcomes, including early mortality, late mortality, sudden unexpected unexplained death, reoperation due to failure of the pulmonary autograft or RVOT reconstruction, thromboembolic events, bleeding events, and endocarditis-related complications, were evaluated.

Results

Upon review of 2,035 publications, 30 studies and 3,156 pediatric patients were included. Patients had a median age of 9.5 years and median follow-up period of 5.7 years. Early mortality rates varied from 0.0 to 17.0% and were increased in the neonatal population. Late mortality rates were much lower (0.04-1.83%/year). Reoperation due to pulmonary autograft failure occurred at rates of 0.37-2.81%/year and reoperation due to RVOT reconstruction failure was required at rates of 0.34-4.76%/year. Thromboembolic, bleeding, and endocarditis events were reported to occur at rates of 0.00-0.58, 0.00-0.39, and 0.00-1.68%/year, respectively.

Conclusions

The Ross operation offers a durable aortic valve replacement (AVR) option in the pediatric population that offers favorable survival, excellent hemodynamics, growth potential, decreased risk of complications, and avoidance of anticoagulation. Larger multi-institutional registries focusing on pediatric patients are necessary to provide more robust evidence to further support use of the Ross procedure in this population.

Residual immune response towards decellularized homografts may be highly individual

 

OBJECTIVES

Decellularized homograft valves (DHVs) have shown promising clinical results, particularly in the treatment of congenital heart disease. However, DHV appears to elicit an immune response in a subset of young patients, indicated by early valve degeneration. As the decellularization process is quality controlled for each DHV, we hypothesized that there may be residual immunogenicity within the extracellular matrix of DHV.

METHODS

A semi-quantitative dot blot analysis was established to screen for preformed recipient antibodies using secondary anti-human antibodies. Fifteen DHV samples (7 aortic, 8 pulmonary) were solubilized and exposed to serum from 20 healthy controls.

RESULTS

The sera from young controls (n = 10, 18–25 years) showed significantly stronger binding of preformed antibodies than sera from older individuals (n = 10, 48–73 years). The difference between the means of arbitrary units was 15.1 ± 6.5 (P = 0.0315). There was high intraindividual variance in the mean amounts of arbitrary units of antibody binding with some healthy controls showing >10 times higher antibody binding towards 2 different DHV. The amount of preformed antibodies bound to DHVs was higher in aortic than in pulmonary DHVs. The mean number of antibody binding (in arbitrary units) was 17.2 ± 4.5 in aortic and 14.5 ± 4.7 in pulmonary DHV (P = 0.27). The amount of preformed antibodies bound to pulmonary DHVs was statistically significantly higher in the sera of healthy males (n = 10) than in the sera of healthy females (n = 10). The mean number of arbitrary units was 17.2 ± 4.2 in male and 11.7 ± 5.3 in female sera (P = 0.036). Antibody binding to aortic DHV was also higher in males, but not significant (18.8 ± 5.0 vs 15.6 ± 4.0). Blood group (ABO) incompatibility between the serum from controls and DHV showed no impact on antibody binding, and there was no age-related impact among DHV donors.

CONCLUSIONS

Residual immunogenicity of decellularized homografts appears to exist despite almost complete cell removal. The established dot blot method allows a semi-quantitative assessment of the individual immune response towards extracellular DHV components and potentially the possibility of preoperative homograft matching.

Staphylococcus aureus adheres avidly to decellularised cardiac homograft tissue in vitro in the fibrinogen-dependent manner

OBJECTIVE

Infective endocarditis remains a severe complication associated with a high morbidity and mortality in patients after heart valve replacement. Exploration of the pathogenesis is of high demand and we, therefore, present a competent model that allows studying bacterial adherence and the role of plasma fibrinogen in this process using a new in-house designed low-volume flow chamber. Three cardiac graft tissues used for pulmonary valve replacement have been tested under shear conditions to investigate the impact of surface composition on the adhesion events.

METHODS

Tissue pieces of cryopreserved homograft (non-decellularised), decellularised homograft and bovine pericardium patch were investigated for fibrinogen binding. Adherence of Staphylococcus aureus to these graft tissues was studied quantitatively under flow conditions in our newly fabricated chamber based on a parallel plates' modality. The method of counting colony-forming units was reliable and reproducible to assess the propensity of different graft materials for bacterial attachment under shear.

RESULTS

Bacterial perfusions over all plasma-precoated tissues identified cryopreserved homograft with the lowest affinity for S. aureus compared to decellularised homograft presenting a significantly higher bacterial adhesion (p < 0.05), which was linked to a more avid fibrinogen binding (p < 0.01). Bovine pericardial patch, as a reference tissue in this study, was confirmed to be the most susceptible tissue graft for the bacterial adhesion, which was in line with our previous work.

CONCLUSION

The two studied homograft tissues showed different levels of bacterial attachment, which might be postulated by the involvement of fibrinogen in the adhesion mechanism(s) shown previously for bovine tissues.

Donor-specific HLA antibodies after fresh decellularized vs cryopreserved native allograft implantation

This study aims to compare the immunogenicity of fresh decellularized with cryopreserved native heart valve allografts to identify potential immunological risks in subsequent organ transplantations. We measured the induction of allogeneic HLA class I and II specific antibodies and characterized donor-specific antibodies by Luminex-based single beads assay in both groups. Serum samples were collected before valve replacement, at 3 and 24 months postoperatively. Donor-specific HLA antibodies were assessed positive if the mean fluorescent intensity (MFI) was >1000. Between November 2016 and April 2017 patients with fresh decellularized homografts (n = 4) and cryopreserved native homografts (n = 4) were analyzed. Patients receiving cryopreserved native allografts reacted with broad HLA-specific antibody response. Antibodies were directed against mismatched HLA antigens of the donors but also against HLA specificities not present on the homograft with many antibodies having mean fluorescence intensity values >10 000. While HLA class I specific antibodies showed a significant increase (P = .002) in their MFI values on day 90, HLA class II specific antibodies did not show a significant increase (P = .069). In the fresh decellularized homografts group, no significant antibody induction was observed. Consequently, the native group presented significantly higher MFIs for HLA antibodies on day 90 compared with the patients receiving decellularized allografts (P = .021). No detectable HLA antibody response was observed after implantation of decellularized in comparison with cryopreserved native allografts. Lower immunogenicity as compared with native homografts might increase the chance of receiving a transplant if will be required later in the life of the patients.

Diepoxy- Versus Glutaraldehyde-Treated Xenografts: Outcomes of Right Ventricular Outflow Tract Reconstruction in Children

BACKGROUND

Xenografts used for right ventricular outflow tract (RVOT) reconstruction are typically treated with glutaraldehyde. However, potential benefit of epoxy treatment was demonstrated in experimental studies. We aimed to compare diepoxy-treated bovine pericardial valved conduits (DE-PVCs) and glutaraldehyde-treated bovine pericardial valved conduits (GA-PVCs) for RVOT reconstruction in pediatric patients.

METHODS

Between 2002 and 2017, 117 patients underwent RVOT reconstruction with PVC in single center: DE-PVC group, n = 39; and GA-PVC group, n = 78. After performing propensity score analysis (1:1) for the entire sample, 29 patients from the DE-PVC group were matched with 29 patients from the GA-PVC group.

RESULTS

There were no conduit-related deaths. In the DE-PVC group, the freedom from conduit failure was 90.9% at four years and 54.3% at eight years postoperatively. In the GA-PVC group, it was 46.3% and 33.1%, respectively. The difference was significant (P = .037). Conduit failure was typically caused by stenosis in both groups. In the DE-PVC group, the main cause of stenosis was xenograft calcification (27.6%); while in the GA-PVC group, it was mostly due to neointimal proliferation (25.0%) and, less often, calcification (14.3%). Conduit thrombosis was the cause of replacement in 6.9% of patients from the GA-PVC group.

CONCLUSIONS

Diepoxy-treated bovine pericardial valved conduit is a suitable alternative to GA-PVC for RVOT reconstruction in pediatric patients. Diepoxy-treated bovine pericardial valved conduits may be less prone to conduit failure and more resistant to neointimal proliferation and conduit thrombosis than GA-PVCs.

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.

Fibrosis in tissue engineering and regenerative medicine: treat or trigger?

Fibrosis is a life-threatening pathological condition resulting from a dysfunctional tissue repair process. There is no efficient treatment and organ transplantation is in many cases the only therapeutic option. Here we review tissue engineering and regenerative medicine (TERM) approaches to address fibrosis in the cardiovascular system, the kidney, the lung and the liver. These strategies have great potential to achieve repair or replacement of diseased organs by cell- and material-based therapies. However, paradoxically, they might also trigger fibrosis. Cases of TERM interventions with adverse outcome are also included in this review. Furthermore, we emphasize the fact that, although organ engineering is still in its infancy, the advances in the field are leading to biomedically relevant in vitro models with tremendous potential for disease recapitulation and development of therapies. These human tissue models might have increased predictive power for human drug responses thereby reducing the need for animal testing.

In vivo performance of freeze-dried decellularized pulmonary heart valve allo- and xenografts orthotopically implanted into juvenile sheep

The decellularization of biological tissues decreases immunogenicity, allows repopulation with cells, and may lead to improved long-term performance after implantation. Freeze drying these tissues would ensure off-the-shelf availability, save storage costs, and facilitates easy transport. This study evaluates the in vivo performance of freeze-dried decellularized heart valves in juvenile sheep. TritonX-100 and sodium dodecylsulfate decellularized ovine and porcine pulmonary valves (PV) were freeze-dried in a lyoprotectant sucrose solution. After rehydration for 24 h, valves were implanted into the PV position in sheep as allografts (fdOPV) and xenografts (fdPPV), while fresh dezellularized ovine grafts (frOPV) were implanted as controls. Functional assessment was performed by transesophageal echocardiography at implantation and at explantation six months later. Explanted grafts were analysed histologically to assess the matrix, and immunofluorescence stains were used to identify the repopulating cells. Although the graft diameters and orifice areas increased, good function was maintained, except for one insufficient, strongly deteriorated frOPV. Cells which were positive for either endothelial or interstitial markers were found in all grafts. In fdPPV, immune-reactive cells were also found. Our findings suggest that freeze-drying does not alter the early hemodynamic performance and repopulation potential of decellularized grafts in vivo, even in the challenging xenogeneic situation. Despite evidence of an immunological reaction for the xenogenic valves, good early functionalities were achieved.

STATEMENT OF SIGNIFICANCE

Decellularized allogeneic heart valves show excellent results as evident from large animal experiments and clinical trials. However, a long-term storing method is needed for an optimal use of this limited resource in the clinical setting, where an optimized matching of graft and recipient is requested. As demonstrated in this study, freeze-dried and freshly decellularized grafts reveal equally good results after implantation in the juvenile sheep concerning function and repopulation with recipients' cells. Thus, freeze-drying arises as a promising method to extend the shelf-life of valvular grafts compared to those stored in antibiotic-solution as currently practised.