Decellularized Pulmonary Xenograft Matrix PplusN versus Cryopreserved Homograft for RVOT Reconstruction during Ross Procedure in Adults

BACKGROUND

 Decellularized pulmonary homografts are being increasingly adopted for right ventricular outflow tract reconstruction in adult patients undergoing the Ross procedure. Few reports presented Matrix PplusN xenograft (Matrix) in a negative light. The objective of this study was to compare our midterm outcomes of Matrix xenograft versus standard cryopreserved pulmonary homograft (CPHG).

METHODS

 Eighteen patients received Matrix xenograft between January 2012 and June 2016, whereas 66 patients received CPHG. Using nonparametric statistical tests and survival analysis, we compared midterm echocardiographic and clinical outcomes between the groups.

RESULTS

 Except for significant age difference (the Matrix group was significantly older with 57 ± 8 years than the CPHG group, 48 ± 9 years, p = 0.02), the groups were similar in all other baseline characteristics. There were no significant differences in cardiopulmonary bypass times (208.3 ± 32.1 vs. 202.8 ± 34.8) or in cross-clamp times (174 ± 33.9 vs. 184.4 ± 31.1) for Matrix and CPHG, respectively. The Matrix group had significantly inferior freedom from reintervention than the CPHG group with 77.8 versus 98.5% (p = 0.02). Freedom from pulmonary valve regurgitation ≥ 2 was not significantly different between the groups with 82.4 versus 90.5% for Matrix versus CPHG, respectively. After median follow-up of 4.9 years, Matrix xenograft developed significantly higher peak pressure gradients compared with CPHG (20.4 ± 15.5 vs. 12.2 ± 9.0 mm Hg; p = 0.04).

CONCLUSION

 After 5 years of clinical and echocardiographic follow-up, the decellularized Matrix xenograft had inferior freedom from reintervention compared with the standard CPHG. Closer follow-up is necessary to avoid progression of valve failure into right ventricular deterioration.

Pediatric pulmonary valve replacements: Clinical challenges and emerging technologies

Congenital heart diseases (CHDs) frequently impact the right ventricular outflow tract, resulting in a significant incidence of pulmonary valve replacement in the pediatric population. While contemporary pediatric pulmonary valve replacements (PPVRs) allow satisfactory patient survival, their biocompatibility and durability remain suboptimal and repeat operations are commonplace, especially for very young patients. This places enormous physical, financial, and psychological burdens on patients and their parents, highlighting an urgent clinical need for better PPVRs. An important reason for the clinical failure of PPVRs is biofouling, which instigates various adverse biological responses such as thrombosis and infection, promoting research into various antifouling chemistries that may find utility in PPVR materials. Another significant contributor is the inevitability of somatic growth in pediatric patients, causing structural discrepancies between the patient and PPVR, stimulating the development of various growth-accommodating heart valve prototypes. This review offers an interdisciplinary perspective on these challenges by exploring clinical experiences, physiological understandings, and bioengineering technologies that may contribute to device development. It thus aims to provide an insight into the design requirements of next-generation PPVRs to advance clinical outcomes and promote patient quality of life.

Pulmonary valve replacement: a new paradigm with tissue engineering

Prevalence of congenital heart diseases worldwide is around 9 per 1000 newborns, 20% of which affect the pulmonary valve or right ventricular outflow tract. As survival after surgical repair of these defects has improved over time, there is the need to address the long-term issues of older children and young adults with "repaired" congenital heart diseases. In recent decades, the most used types of valves are the mechanical and bioprosthetic valves. Despite improving patients' quality of life, these effects are suboptimal due to their limitations, such as the inability to grow and adapt to hemodynamic changes. These issues have led to the search for living valve solutions through tissue engineering to respond to these challenges. This review aims to review the performance of traditional pulmonary valves and understand how tissue engineering-based valves can improve the management of these patients.

Decellularized versus cryopreserved pulmonary allografts for right ventricular outflow tract reconstruction during the Ross procedure: a meta-analysis of short- and long-term outcomes

Background

The ideal conduit for repair of the right ventricular outflow tract (RVOT) during the Ross procedure remains unclear and has yet to be fully elucidated. We perform a pairwise meta-analysis to compare the short-term and long-term outcomes of decellularized versus cryopreserved pulmonary allografts for RVOT reconstruction during the Ross procedure.

Main body

After a comprehensive literature search, studies comparing decellularized and cryopreserved allografts for patients undergoing RVOT reconstruction during the Ross procedure were pooled to perform a pairwise meta-analysis using the random-effects model. Primary outcomes were early mortality and follow-up allograft dysfunction. Secondary outcomes were reintervention rates and follow-up endocarditis. A total of 4 studies including 1687 patients undergoing RVOT reconstruction during the Ross procedure were included. A total of 812 patients received a decellularized pulmonary allograft, while 875 received a cryopreserved pulmonary allograft. Compared to cryopreserved allografts, the decellularized group showed similar rates of early mortality (odds ratio, 0.55, 95% confidence interval, 0.21–1.41, P = 0.22). At a mean follow-up period of 5.89 years, no significant difference was observed between the two groups for follow-up allograft dysfunction (hazard ratio, 0.65, 95% confidence interval, 0.20–2.14, P = 0.48). Similarly, no difference was seen in reintervention rates (hazard ratio, 0.54, 95% confidence interval, 0.09–3.12, P = 0.49) nor endocarditis (hazard ratio, 0.30, 95% confidence interval, 0.07–1.35, P = 0.12) at a mean follow-up of 4.85 and 5.75 years, respectively.

Conclusions

Decellularized and cryopreserved pulmonary allografts are associated with similar postoperative outcomes for RVOT reconstruction during the Ross procedure. Larger propensity-matched and randomized control trials are necessary to elucidate the efficacy of decellularized allografts compared to cryopreserved allografts in the setting of the Ross.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43044-021-00226-w.

Systematic review and meta-analysis of long-term outcomes in adults undergoing the Ross procedure

Background

The management of aortic valve disease is becoming increasingly complicated with the evolution of treatment options available to cardiac surgeons and cardiologist. Pulmonary autograft replacement of the aortic valve, commonly known as the Ross procedure, involves excision of the pulmonary valve from the right ventricular outflow tract and implantation in the aortic position. This systematic review aims to evaluate the long-term outcomes, following the Ross procedure.

Methods

An electronic search strategy queried five online medical referencing databases from inception to 21 August 2020. All studies detailing the long-term outcomes of adults undergoing the Ross procedure were included. A random effects model was used to determine pooled continuous data. Enhanced secondary survival analysis was performed on reconstructed individual patient data.

Results

Twenty-three studies were included in the qualitative synthesis, including a total of 6,278 patients with a mean follow-up duration of 6.0±2.8 years. Long-term survival was 95.6%, 91.8%, 86.3% and 80.5% at five, ten, fifteen and twenty years, respectively. Freedom from autograft reoperation was 95.7%, 91.2%, 84.9% and 76.1% at five, ten, fifteen and twenty years, respectively.

Conclusions

When performed in experienced centres and for appropriately selected patients, the Ross procedure represents a durable replacement of the aortic valve with excellent long-term survival.

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.

The long term results of the Ross procedure: The importance of candidate selection

The Ross procedure has been considered in children as an optimal surgical procedure due to potential growth of the aortic annulus, lack of anticoagulation requirement, very low morbidity rate and excellent survival. Five-hundred-thirty-six (366 male, mean age 29.4 ± 11.1 years) underwent Ross procedure between 1990 and 2016 and had complete clinical and echocardiographic follow-up. Mean follow-up was 16.3 ± 4.9 years. Patients were divided in 2 groups according to age at surgery. Group 1 consisted of 320 (60%) patients less than 18 years old (223 male, mean age at surgery of 9.5 ± 5.6 years). Group 2 consisted of 216 (40%) patients older than 18 years of age (143 male, mean age at surgery of 26.3 ± 8.2 years). One-hundred-thirty (24%) patients had a redo procedure or surgery. Freedom from all re-operation and or percutaneous reintervention on either the aortic and pulmonary valves was 99% after 1 year, 94% after 5 years, 89% after 10 years, 83% after 15 years and 78% after 20 years. Freedom from redo surgery for AV 99% after 1 year, 94% after 5 years, 90% after 10 years, 81% after 15 years and 80% after 20 years. Freedom from redo surgery for PV was 100% after 1 year, 95% after 5 years, 89% after 10 years, 78% after 15 years and 76% after 20 years. The ideal candidate for Ross operation is a patient with congenital aetiology and an aortic root diameter ≤ 15 mm/m². A pulmonary fresh preserved homograft seems to perform better on the long term.

Clinical performance of decellularized heart valves versus standard tissue conduits: a systematic review and meta-analysis

Background

Valve replacement surgery is the definitive management strategy for patients with severe valvular disease. However, valvular conduits currently in clinical use are associated with significant limitations. Tissue-engineered (decellularized) heart valves are alternative prostheses that have demonstrated promising early results. The purpose of this systematic review and meta-analysis is to perform robust evaluation of the clinical performance of decellularized heart valves implanted in either outflow tract position, in comparison with standard tissue conduits.

Methods

Systematic searches were conducted in the PubMed, Scopus, and Web of Science databases for articles in which outcomes between decellularized heart valves surgically implanted within either outflow tract position of human subjects and standard tissue conduits were compared. Primary endpoints included postoperative mortality and reoperation rates. Meta-analysis was performed using a random-effects model via the Mantel-Haenszel method.

Results

Seventeen articles were identified, of which 16 were included in the meta-analysis. In total, 1418 patients underwent outflow tract reconstructions with decellularized heart valves and 2725 patients received standard tissue conduits. Decellularized heart valves were produced from human pulmonary valves and implanted within the right ventricular outflow tract in all cases. Lower postoperative mortality (4.7% vs. 6.1%; RR 0.94, 95% CI: 0.60–1.47; P = 0.77) and reoperation rates (4.8% vs. 7.4%; RR 0.55, 95% CI: 0.36–0.84; P = 0.0057) were observed in patients with decellularized heart valves, although only reoperation rates were statistically significant. There was no statistically significant heterogeneity between the analyzed articles (I² = 31%, P = 0.13 and I² = 33%, P = 0.10 respectively).

Conclusions

Decellularized heart valves implanted within the right ventricular outflow tract have demonstrated significantly lower reoperation rates when compared to standard tissue conduits. However, in order to allow for more accurate conclusions about the clinical performance of decellularized heart valves to be made, there need to be more high-quality studies with greater consistency in the reporting of clinical outcomes.

Progressive Reinvention or Destination Lost? Half a Century of Cardiovascular Tissue Engineering

The concept of tissue engineering evolved long before the phrase was forged, driven by the thromboembolic complications associated with the early total artificial heart programs of the 1960s. Yet more than half a century of dedicated research has not fulfilled the promise of successful broad clinical implementation. A historical account outlines reasons for this scientific impasse. For one, there was a disconnect between distinct eras each characterized by different clinical needs and different advocates. Initiated by the pioneers of cardiac surgery attempting to create neointimas on total artificial hearts, tissue engineering became fashionable when vascular surgeons pursued the endothelialisation of vascular grafts in the late 1970s. A decade later, it were cardiac surgeons again who strived to improve the longevity of tissue heart valves, and lastly, cardiologists entered the fray pursuing myocardial regeneration. Each of these disciplines and eras started with immense enthusiasm but were only remotely aware of the preceding efforts. Over the decades, the growing complexity of cellular and molecular biology as well as polymer sciences have led to surgeons gradually being replaced by scientists as the champions of tissue engineering. Together with a widening chasm between clinical purpose, human pathobiology and laboratory-based solutions, clinical implementation increasingly faded away as the singular endpoint of all strategies. Moreover, a loss of insight into the healing of cardiovascular prostheses in humans resulted in the acceptance of misleading animal models compromising the translation from laboratory to clinical reality. This was most evident in vascular graft healing, where the two main impediments to the in-situ generation of functional tissue in humans remained unheeded–the trans-anastomotic outgrowth stoppage of endothelium and the build-up of an impenetrable surface thrombus. To overcome this dead-lock, research focus needs to shift from a biologically possible tissue regeneration response to one that is feasible at the intended site and in the intended host environment of patients. Equipped with an impressive toolbox of modern biomaterials and deep insight into cues for facilitated healing, reconnecting to the “user needs” of patients would bring one of the most exciting concepts of cardiovascular medicine closer to clinical reality.

A Comprehensive Comparison of Bovine and Porcine Decellularized Pericardia: New Insights for Surgical Applications

Xenogeneic pericardium-based substitutes are employed for several surgical indications after chemical shielding, limiting their biocompatibility and therapeutic durability. Adverse responses to these replacements might be prevented by tissue decellularization, ideally removing cells and preserving the original extracellular matrix (ECM). The aim of this study was to compare the mostly applied pericardia in clinics, i.e. bovine and porcine tissues, after their decellularization, and obtain new insights for their possible surgical use. Bovine and porcine pericardia were submitted to TRICOL decellularization, based on osmotic shock, detergents and nuclease treatment. TRICOL procedure resulted in being effective in cell removal and preservation of ECM architecture of both species' scaffolds. Collagen and elastin were retained but glycosaminoglycans were reduced, significantly for bovine scaffolds. Tissue hydration was varied by decellularization, with a rise for bovine pericardia and a decrease for porcine ones. TRICOL significantly increased porcine pericardial thickness, while a non-significant reduction was observed for the bovine counterpart. The protein secondary structure and thermal denaturation profile of both species' scaffolds were unaltered. Both pericardial tissues showed augmented biomechanical compliance after decellularization. The ECM bioactivity of bovine and porcine pericardia was unaffected by decellularization, sustaining viability and proliferation of human mesenchymal stem cells and endothelial cells. In conclusion, decellularized bovine and porcine pericardia demonstrate possessing the characteristics that are suitable for the creation of novel scaffolds for reconstruction or replacement: differences in water content, thickness and glycosaminoglycans might influence some of their biomechanical properties and, hence, their indication for surgical use.

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.

Decellularised scaffolds: just a framework? Current knowledge and future directions

The use of decellularised matrices as scaffolds offers the advantage of great similarity with the tissue to be replaced. Moreover, decellularised tissues and organs can be repopulated with the patient's own cells to produce bespoke therapies. Great progress has been made in research and development of decellularised scaffolds, and more recently, these materials are being used in exciting new areas like hydrogels and bioinks. However, much effort is still needed towards preserving the original extracellular matrix composition, especially its minor components, assessing its functionality and scaling up for large tissues and organs. Emphasis should also be placed on developing new decellularisation methods and establishing minimal criteria for assessing the success of the decellularisation process. The aim of this review is to critically review the existing literature on decellularised scaffolds, especially on the preparation of these matrices, and point out areas for improvement, finishing with alternative uses of decellularised scaffolds other than tissue and organ reconstruction. Such uses include three-dimensional ex vivo platforms for idiopathic diseases and cancer modelling.

Pulmonary Valve Function Late After Ross Procedure in 443 Adult Patients

BACKGROUND

Limited data exist on long-term pulmonary valve function after the Ross procedure. This study sought to determine the long-term function of the pulmonary valve in 443 consecutive adult patients who underwent a Ross procedure.

METHODS

All 443 patients who underwent a Ross procedure between November 1992 and March 2018 were reviewed retrospectively. All underwent pulmonary valve replacement using a cryopreserved pulmonary allograft. Freedom from the study's outcomes were calculated using Kaplan Meier survival. Risk factors for valve failure were analyzed using Cox regression.

RESULTS

Mean age at time of operation was 39 years (range: 15-66 years). There was 1 (0.2%, 1 of 443) operative mortality. Nine patients required reintervention on the pulmonary allograft at a mean 6.1 years (range: 1-12 years) after Ross procedure. Patients required pulmonary allograft reintervention for infective endocarditis (n = 4), severe pulmonary stenosis (n = 4), or severe pulmonary regurgitation (n = 1). Freedom from pulmonary allograft reintervention was 98.9% (95% confidence interval [CI] 97.1%-99.6%), 97.7% (95% CI 95.1%-98.9%), 96.6% (95% CI 93.3%-98.3%), and 96.6% (95% CI 93.3%-98.3%) at 5, 10, 15, and 20 years, respectively. Freedom from pulmonary allograft dysfunction (at least moderate pulmonary regurgitation and/or mean systolic gradient ≥ 25 mm Hg and/or reintervention) was 94.5% (95% CI 91.6%-96.4%), 88.1% (95% CI 83.6%-91.4%), 84.9% (95% CI 79.6%-88.9%), and 78.3% (95% CI 69.5%-84.9%) at 5, 10, 15, and 20 years, respectively. No risk factors were identified to influence pulmonary valve durability.

CONCLUSIONS

The pulmonary valve allograft gives excellent long-term function when used in adults undergoing the Ross procedure. Reintervention on the pulmonary valve is rare and significant pulmonary allograft dysfunction is uncommon.

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.