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Zilla P, Human P, Pennel T. Mechanical valve replacement for patients with rheumatic heart disease: the reality of INR control in Africa and beyond. Front Cardiovasc Med 2024; 11:1347838. [PMID: 38404722 PMCID: PMC10884232 DOI: 10.3389/fcvm.2024.1347838] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Accepted: 01/23/2024] [Indexed: 02/27/2024] Open
Abstract
The majority of patients requiring heart valve replacement in low- to middle-income countries (LMICs) need it for rheumatic heart disease (RHD). While the young age of such patients largely prescribes replacement with mechanical prostheses, reliable anticoagulation management is often unattainable under the prevailing socioeconomic circumstances. Cases of patients with clotted valves presenting for emergency surgery as a consequence of poor adherence to anticoagulation control are frequent. The operative mortality rates of reoperations for thrombosed mechanical valves are several times higher than those for tissue valves, and long-term results are also disappointing. Under-anticoagulation prevails in these regions that has clearly been linked to poor international normalised ratio (INR) monitoring. In industrialised countries, safe anticoagulation is defined as >60%-70% of the time in the therapeutic range (TTR). In LMICs, the TTR has been found to be in the range of twenty to forty percent. In this study, we analysed >20,000 INR test results of 552 consecutive patients receiving a mechanical valve for RHD. Only 27% of these test results were in the therapeutic range, with the vast majority (61%) being sub-therapeutic. Interestingly, the post-operative frequency of INR tests of one every 3-4 weeks in year 1 had dropped to less than 1 per year by year 7. LMICs need to use clinical judgement and assess the probability of insufficient INR monitoring prior to uncritically applying Western guidelines predominantly based on chronological age. The process of identification of high-risk subgroups in terms of non-adherence to anticoagulation control should take into account both the adherence history of >50% of patients with RHD who were in chronic atrial fibrillation prior to surgery as well as geographic and socioeconomic circumstances.
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Affiliation(s)
- Peter Zilla
- Christiaan Barnard Division of Cardiothoracic Surgery, University of Cape Town and Groote Schuur Hospital, Cape Town, South Africa
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Aldersley T, Brooks A, Human P, Lawrenson J, Comitis G, De Decker R, Fourie B, Manganyi R, Pribut H, Salie S, Swanson L, Zühlke L. The impact of COVID-19 on a South African pediatric cardiac service: implications and insights into service capacity. Front Public Health 2023; 11:1177365. [PMID: 37234766 PMCID: PMC10206042 DOI: 10.3389/fpubh.2023.1177365] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Accepted: 04/05/2023] [Indexed: 05/28/2023] Open
Abstract
Background and Objectives The Western Cape public pediatric cardiac service is under-resourced. COVID-19 regulations are likely to have long-term effects on patient care but may provide insight into service capacity requirements. As such, we aimed to quantify the impact of COVID-19 regulations on this service. Methods An uncontrolled retrospective pre-post study of all presenting patients over two, one-year periods; the pre-COVID-19 period (01/03/2019-29/02/2020) and the peri-COVID-19 period (01/03/2020-28/02/2021). Results Admissions decreased by 39% (624 to 378) and cardiac surgeries decreased by 29% (293 to 208) in the peri-COVID-19 period, with an increase in urgent cases (PR:5.99, 95%CI:3.58-10.02, p < 0.001). Age at surgery was lower in the peri-COVID-19 period, 7.2 (2.4-20.4) vs. 10.8 (4.8-49.2) months (p < 0.05), likewise, age at surgery for transposition of the great arteries (TGA) was lower peri-COVID-19, 15 (IQR:11.2-25.5) vs. 46 (IQR:11-62.5) days (p < 0.05). Length of stay 6 (IQR:2-14) vs. 3 days (IQR:1-9) (p < 0.001), complications (PR:1.21, 95%CI:1.01-1.43, p < 0.05), and age-adjusted delayed-sternal-closure rates (PR:3.20, 95%CI:1.09-9.33, p < 0.05) increased peri-COVID-19. Conclusion Cardiac procedures were significantly reduced in the peri-COVID-19 period which will have implications on an overburdened service and ultimately, patient outcomes. COVID-19 restrictions on elective procedures freed capacity for urgent cases, demonstrated by the absolute increase in urgent cases and significant decrease in age at TGA-surgery. This facilitated intervention at the point of physiological need, albeit at the expense of elective procedures, and also revealed insights into capacity requirements of the Western Cape. These data emphasize the need for an informed strategy to increase capacity and reduce backlog whilst ensuring minimal morbidity and mortality.Graphical Abstract.
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Affiliation(s)
- Thomas Aldersley
- Department of Pediatrics and Child Health, Pediatric Cardiology, University of Cape Town, Cape Town, South Africa
- Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
| | - Andre Brooks
- Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
- Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa
- Groote Schuur Hospital, Cape Town, South Africa
| | - Paul Human
- Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa
- Groote Schuur Hospital, Cape Town, South Africa
| | - John Lawrenson
- Department of Pediatrics and Child Health, Pediatric Cardiology, University of Cape Town, Cape Town, South Africa
- Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health, University of Stellenbosch, Cape Town, South Africa
- Tygerberg Hospital, Cape Town, South Africa
| | - George Comitis
- Department of Pediatrics and Child Health, Pediatric Cardiology, University of Cape Town, Cape Town, South Africa
- Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
| | - Rik De Decker
- Department of Pediatrics and Child Health, Pediatric Cardiology, University of Cape Town, Cape Town, South Africa
- Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
| | - Barend Fourie
- Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health, University of Stellenbosch, Cape Town, South Africa
- Tygerberg Hospital, Cape Town, South Africa
| | - Rodgers Manganyi
- Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
- Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa
- Groote Schuur Hospital, Cape Town, South Africa
| | - Harold Pribut
- Department of Pediatrics and Child Health, Pediatric Cardiology, University of Cape Town, Cape Town, South Africa
- Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
| | - Shamiel Salie
- Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
- Department of Pediatrics and Child Health, Pediatric Intensive and Critical Care Unit, University of Cape Town, Cape Town, South Africa
| | - Lenise Swanson
- Department of Pediatrics and Child Health, Pediatric Cardiology, University of Cape Town, Cape Town, South Africa
- Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
| | - Liesl Zühlke
- Department of Pediatrics and Child Health, Pediatric Cardiology, University of Cape Town, Cape Town, South Africa
- Red Cross War Memorial Children’s Hospital, Cape Town, South Africa
- South African Medical Research Council, Cape Town, South Africa
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Ngarande E, Doubell E, Tamgue O, Mano M, Human P, Giacca M, Davies NH. Modified fibrin hydrogel for sustained delivery of RNAi lipopolyplexes in skeletal muscle. Regen Biomater 2022; 10:rbac101. [PMID: 36726610 PMCID: PMC9887344 DOI: 10.1093/rb/rbac101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 11/02/2022] [Accepted: 11/24/2022] [Indexed: 12/15/2022] Open
Abstract
RNA interference is a promising therapeutical approach presently hindered by delivery concerns such as rapid RNA degradation and targeting of individual tissues. Injectable hydrogels are one potentially simple and direct route towards overcoming these barriers. Here we report on the utility of a combination of a mildly modified form of the clinically utilised fibrin hydrogel with Invivofectamine® 3.0, a lipid nonviral transfection vector, for local and sustained release. PEGylation of fibrin allowed for controlled release of small interfering RNA (siRNA)-lipopolyplexes for at least 10 days and greatly increased the stability of fibrin in vitro and in vivo. A 3D cell culture model and a release study showed transfection efficacy of siRNA-lipopolyplexes was retained for a minimum of 7 days. Injection in conjunction with PEGylated-fibrinogen significantly increased retention of siRNA-lipopolyplexes in mouse skeletal muscle and enhanced knockdown of myostatin mRNA that correlated with muscle growth. Thus, the increased efficacy observed here for the combination of a lipid nanoparticle, the only type of nonviral vector approved for the clinic, with fibrin, might allow for more rapid translation of injectable hydrogel-based RNA interference.
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Affiliation(s)
- Ellen Ngarande
- Cardiovascular Research Unit, Department of Surgery, Faculty of Health Sciences, University of Cape Town, Observatory 7925, South Africa
| | - Emma Doubell
- Cardiovascular Research Unit, Department of Surgery, Faculty of Health Sciences, University of Cape Town, Observatory 7925, South Africa
| | | | - Manuel Mano
- King’s College London, British Heart Foundation Centre of Research Excellence, School of Cardiovascular Medicine & Sciences, WC2R 2LS, London, UK
| | - Paul Human
- Cardiovascular Research Unit, Department of Surgery, Faculty of Health Sciences, University of Cape Town, Observatory 7925, South Africa
| | - Mauro Giacca
- King’s College London, British Heart Foundation Centre of Research Excellence, School of Cardiovascular Medicine & Sciences, WC2R 2LS, London, UK
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Saacks NA, Eales J, Spracklen TF, Aldersley T, Human P, Verryn M, Lawrenson J, Cupido B, Comitis G, De Decker R, Fourie B, Swanson L, Joachim A, Brooks A, Ramesar R, Shaboodien G, Keavney BD, Zühlke LJ. Investigation of Copy Number Variation in South African Patients With Congenital Heart Defects. Circ Genom Precis Med 2022; 15:e003510. [PMID: 36205932 PMCID: PMC9770125 DOI: 10.1161/circgen.121.003510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Accepted: 06/27/2022] [Indexed: 11/05/2022]
Abstract
BACKGROUND Congenital heart disease (CHD) is a leading non-infectious cause of pediatric morbidity and mortality worldwide. Although the etiology of CHD is poorly understood, genetic factors including copy number variants (CNVs) contribute to the risk of CHD in individuals of European ancestry. The presence of rare CNVs in African CHD populations is unknown. This study aimed to identify pathogenic and likely pathogenic CNVs in South African patients with CHD. METHODS Genotyping was performed on 90 patients with nonsyndromic CHD using the Affymetrix CytoScan HD platform. These data were used to identify large, rare CNVs in known CHD-associated genes and candidate genes. RESULTS We identified eight CNVs overlapping known CHD-associated genes (GATA4, CRKL, TBX1, FLT4, B3GAT3, NSD1) in six patients. The analysis also revealed CNVs encompassing five candidate genes likely to play a role in the development of CHD (DGCR8, KDM2A, JARID2, FSTL1, CYFIP1) in five patients. One patient was found to have 47, XXY karyotype. We report a total discovery yield of 6.7%, with 5.6% of the cohort carrying pathogenic or likely pathogenic CNVs expected to cause the observed phenotypes. CONCLUSIONS In this study, we show that chromosomal microarray is an effective technique for identifying CNVs in African patients diagnosed with CHD and have demonstrated results similar to previous CHD genetic studies in Europeans. Novel potential CHD genes were also identified, indicating the value of genetic studies of CHD in ancestrally diverse populations.
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Affiliation(s)
- Nicole A. Saacks
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health (N.A.S., T.F.S., T.A., J.L., G.C., R.D.D., L.S., A.J., L.J.Z.)
| | - James Eales
- Division of Cardiovascular Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, United Kingdom (J.E., B.D.K.)
| | - Timothy F. Spracklen
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health (N.A.S., T.F.S., T.A., J.L., G.C., R.D.D., L.S., A.J., L.J.Z.)
- Department of Medicine, Cape Heart Institute (T.F.S., G.S., L.J.Z.)
| | - Thomas Aldersley
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health (N.A.S., T.F.S., T.A., J.L., G.C., R.D.D., L.S., A.J., L.J.Z.)
| | - Paul Human
- Chris Barnard Division of Cardiothoracic Surgery, Department of Medicine, Faculty of Health Sciences (P.H., A.B.)
| | - Mark Verryn
- Cardiovascular Genetics Laboratory, Hatter Institute for Cardiovascular Research in Africa (M.V., G.S.)
| | - John Lawrenson
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health (N.A.S., T.F.S., T.A., J.L., G.C., R.D.D., L.S., A.J., L.J.Z.)
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health, University of Stellenbosch, Cape Town, South Africa (J.L., B.F.)
| | - Blanche Cupido
- Division of Cardiology, Department of Medicine, Groote Schuur Hospital, Faculty of Health Sciences (B.C., L.J.Z.)
| | - George Comitis
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health (N.A.S., T.F.S., T.A., J.L., G.C., R.D.D., L.S., A.J., L.J.Z.)
| | - Rik De Decker
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health (N.A.S., T.F.S., T.A., J.L., G.C., R.D.D., L.S., A.J., L.J.Z.)
| | - Barend Fourie
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health, University of Stellenbosch, Cape Town, South Africa (J.L., B.F.)
| | - Lenise Swanson
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health (N.A.S., T.F.S., T.A., J.L., G.C., R.D.D., L.S., A.J., L.J.Z.)
| | - Alexia Joachim
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health (N.A.S., T.F.S., T.A., J.L., G.C., R.D.D., L.S., A.J., L.J.Z.)
| | - Andre Brooks
- Chris Barnard Division of Cardiothoracic Surgery, Department of Medicine, Faculty of Health Sciences (P.H., A.B.)
| | - Raj Ramesar
- MRC Genomic & Precision Medicine Research Unit, Division of Human Genetics, Dept of Pathology, Institute for Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa (R.R.)
| | - Gasnat Shaboodien
- Department of Medicine, Cape Heart Institute (T.F.S., G.S., L.J.Z.)
- Cardiovascular Genetics Laboratory, Hatter Institute for Cardiovascular Research in Africa (M.V., G.S.)
| | - Bernard D. Keavney
- Division of Cardiovascular Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, United Kingdom (J.E., B.D.K.)
| | - Liesl J. Zühlke
- Division of Pediatric Cardiology, Department of Pediatrics and Child Health (N.A.S., T.F.S., T.A., J.L., G.C., R.D.D., L.S., A.J., L.J.Z.)
- Department of Medicine, Cape Heart Institute (T.F.S., G.S., L.J.Z.)
- Division of Cardiology, Department of Medicine, Groote Schuur Hospital, Faculty of Health Sciences (B.C., L.J.Z.)
- South African Medical Research Council, Cape Town (L.J.Z.)
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Meyer HM, Marange-Chikuni D, Anaesthesia MM, Zühlke L, Roussow B, Human P, Brooks A. Outcomes After Bidirectional Glenn Shunt in a Tertiary-Care Pediatric Hospital in South Africa. J Cardiothorac Vasc Anesth 2022; 36:1573-1581. [PMID: 35151565 DOI: 10.1053/j.jvca.2022.01.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Revised: 12/29/2021] [Accepted: 01/03/2022] [Indexed: 11/11/2022]
Abstract
OBJECTIVES Large data sets have been published on short- and long-term outcomes following bidirectional Glenn surgery (BDG), or partial cavopulmonary connection, in high-income countries. Data from low-income and middle-income countries are few and often limited to the immediate postoperative period. The primary outcome was any in-hospital postoperative complication, assessed according to predefined criteria, in children who underwent BDG surgery at Red Cross War Memorial Children's Hospital. DESIGN A retrospective cohort study. SETTING A tertiary teaching hospital. PARTICIPANTS The study authors identified 61 children (<18 years of age) who underwent BDG over 8 years. The median age of patients undergoing BDG was 2.5 years (interquartile range, 1.4-5.5 years). INTERVENTIONS BDG surgery. MEASUREMENTS AND MAIN RESULTS Thirty-five patients (57.4%) had a postoperative complication, with some patients (17 of 61, 27.9%) having more than 1 complication. The most frequent complications were infective (29.5%). Univariate analysis found that postoperative complications were associated with the use of nitric oxide (p = 0.004) and a longer duration of anesthesia (p = 0.045) and surgery (p = 0.004). Patients with complications spent longer in the pediatric intensive care unit (ICU) (p < 0.001) and in the hospital (p < 0.012). On multivariate analysis, a priori risk factors based on previous studies were not found to be statistically significant. A total of 37.3% of patients completed their single-ventricle palliation, and 30.5% of patients were lost to follow-up. CONCLUSIONS Important findings were the older age at which the BDG was performed compared to high-income countries, an acceptable mortality rate of 3.3%, infection being the most common complication, the association of a complication with increased ICU and hospital lengths of stay, and the high rate of patients lost to follow-up.
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Affiliation(s)
- Heidi M Meyer
- Division of Paediatric Anaesthesia, Department of Anaesthesia & Perioperative Medicine, Faculty of Health Sciences, University of Cape Town, Red Cross War Memorial Children's Hospital, Cape Town, South Africa.
| | - Danai Marange-Chikuni
- Department of Anaesthesia and Critical Care Medicine, Faculty of Medicine and Health Sciences, University of Zimbabwe, Sally Mugabe Central Hospital, Harare, Zimbabwe
| | - MMed Anaesthesia
- Department of Anaesthesia and Critical Care Medicine, Faculty of Medicine and Health Sciences, University of Zimbabwe, Sally Mugabe Central Hospital, Harare, Zimbabwe
| | - Liesl Zühlke
- Division of Paediatric Cardiology, Department of Paediatrics and Child Health, Faculty of Health Sciences, University of Cape Town, Red Cross War Memorial Children's Hospital, Cape Town, South Africa
| | - Beyra Roussow
- Division of Paediatric Critical Care, Department of Paediatrics and Child Health, Faculty of Health Sciences, University of Cape Town, Red Cross War Memorial Children's Hospital, Cape Town, South Africa
| | - Paul Human
- Chris Barnard Division of Cardiothoracic Surgery and Cardiovascular Research Unit, Department of Surgery, Faculty of Health Sciences, University of Cape Town, Groote Schuur Hospital, Cape Town, South Africa
| | - Andre Brooks
- Chris Barnard Division of Cardiothoracic Surgery and Cardiovascular Research Unit, Department of Surgery, Faculty of Health Sciences, University of Cape Town, Red Cross War Memorial Children's Hospital, Cape Town, South Africa
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Appa H, Park K, Bezuidenhout D, van Breda B, de Jongh B, de Villiers J, Chacko R, Scherman J, Ofoegbu C, Swanevelder J, Cousins M, Human P, Smith R, Vogt F, Podesser BK, Schmitz C, Conradi L, Treede H, Schröfel H, Fischlein T, Grabenwöger M, Luo X, Coombes H, Matskeplishvili S, Williams DF, Zilla P. The Technological Basis of a Balloon-Expandable TAVR System: Non-occlusive Deployment, Anchorage in the Absence of Calcification and Polymer Leaflets. Front Cardiovasc Med 2022; 9:791949. [PMID: 35310972 PMCID: PMC8928444 DOI: 10.3389/fcvm.2022.791949] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2021] [Accepted: 01/18/2022] [Indexed: 12/14/2022] Open
Abstract
Leaflet durability and costs restrict contemporary trans-catheter aortic valve replacement (TAVR) largely to elderly patients in affluent countries. TAVR that are easily deployable, avoid secondary procedures and are also suitable for younger patients and non-calcific aortic regurgitation (AR) would significantly expand their global reach. Recognizing the reduced need for post-implantation pacemakers in balloon-expandable (BE) TAVR and the recent advances with potentially superior leaflet materials, a trans-catheter BE-system was developed that allows tactile, non-occlusive deployment without rapid pacing, direct attachment of both bioprosthetic and polymer leaflets onto a shape-stabilized scallop and anchorage achieved by plastic deformation even in the absence of calcification. Three sizes were developed from nickel-cobalt-chromium MP35N alloy tubes: Small/23 mm, Medium/26 mm and Large/29 mm. Crimp-diameters of valves with both bioprosthetic (sandwich-crosslinked decellularized pericardium) and polymer leaflets (triblock polyurethane combining siloxane and carbonate segments) match those of modern clinically used BE TAVR. Balloon expansion favors the wing-structures of the stent thereby creating supra-annular anchors whose diameter exceeds the outer diameter at the waist level by a quarter. In the pulse duplicator, polymer and bioprosthetic TAVR showed equivalent fluid dynamics with excellent EOA, pressure gradients and regurgitation volumes. Post-deployment fatigue resistance surpassed ISO requirements. The radial force of the helical deployment balloon at different filling pressures resulted in a fully developed anchorage profile of the valves from two thirds of their maximum deployment diameter onwards. By combining a unique balloon-expandable TAVR system that also caters for non-calcific AR with polymer leaflets, a powerful, potentially disruptive technology for heart valve disease has been incorporated into a TAVR that addresses global needs. While fulfilling key prerequisites for expanding the scope of TAVR to the vast number of patients of low- to middle income countries living with rheumatic heart disease the system may eventually also bring hope to patients of high-income countries presently excluded from TAVR for being too young.
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Affiliation(s)
- Harish Appa
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - Kenneth Park
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - Deon Bezuidenhout
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
- Cardiovascular Research Unit, University of Cape Town, Cape Town, South Africa
| | - Braden van Breda
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - Bruce de Jongh
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - Jandré de Villiers
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - Reno Chacko
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - Jacques Scherman
- Cardiovascular Research Unit, University of Cape Town, Cape Town, South Africa
- Chris Barnard Division for Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa
| | - Chima Ofoegbu
- Cardiovascular Research Unit, University of Cape Town, Cape Town, South Africa
- Chris Barnard Division for Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa
| | - Justiaan Swanevelder
- Department of Anaesthesia and Perioperative Medicine, University of Cape Town, Cape Town, South Africa
| | - Michael Cousins
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - Paul Human
- Cardiovascular Research Unit, University of Cape Town, Cape Town, South Africa
- Chris Barnard Division for Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa
| | - Robin Smith
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - Ferdinand Vogt
- Deparment of Cardiac Surgery, Artemed Clinic Munich South, Munich, Germany
- Department of Cardiac Surgery, Klinikum Nürnberg, Paracelsus Medical University, Nuremberg, Germany
| | - Bruno K. Podesser
- Center for Biomedical Research, Medical University of Vienna, Vienna, Austria
| | - Christoph Schmitz
- Auto Tissue Berlin, Berlin, Germany
- Department of Cardiac Surgery, University of Munich, Munich, Germany
| | - Lenard Conradi
- Department of Cardiovascular Surgery, University Heart Center, Hamburg, Germany
| | - Hendrik Treede
- Department of Cardiac and Vascular Surgery, University Hospital, Mainz, Germany
| | - Holger Schröfel
- Department of Cardiovascular Surgery, University Heart Center, Freiburg, Germany
| | - Theodor Fischlein
- Department of Cardiac Surgery, Klinikum Nürnberg, Paracelsus Medical University, Nuremberg, Germany
| | - Martin Grabenwöger
- Department of Cardiovascular Surgery, Vienna North Hospital, Vienna, Austria
| | - Xinjin Luo
- Department of Cardiac Sugery, Fu Wai Hospital, Peking Union Medical College, Beijing, China
| | - Heather Coombes
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | | | - David F. Williams
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
- Wake Forest Institute of Regenerative Medicine, Wake Forest School of Medicine, Winston-Salem, NC, United States
| | - Peter Zilla
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
- Cardiovascular Research Unit, University of Cape Town, Cape Town, South Africa
- Chris Barnard Division for Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa
- Cape Heart Centre, University of Cape Town, Cape Town, South Africa
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7
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Human P, Bezuidenhout D, Aikawa E, Zilla P. Residual Bioprosthetic Valve Immunogenicity: Forgotten, Not Lost. Front Cardiovasc Med 2022; 8:760635. [PMID: 35059444 PMCID: PMC8764456 DOI: 10.3389/fcvm.2021.760635] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Accepted: 12/13/2021] [Indexed: 12/02/2022] Open
Abstract
Despite early realization of the need to control inherent immunogenicity of bioprosthetic replacement heart valves and thereby mitigate the ensuing host response and its associated pathology, including dystrophic calcification, the problem remains unresolved to this day. Concerns over mechanical stiffness associated with prerequisite high cross-link density to effect abrogation of this response, together with the insinuated role of leaching glutaraldehyde monomer in subsequent dystrophic mineralization, have understandably introduced compromises. These have become so entrenched as a benchmark standard that residual immunogenicity of the extracellular matrix has seemingly been relegated to a very subordinate role. Instead, focus has shifted toward the removal of cellular compartment antigens renowned for their implication in the failure of vascularized organ xenotransplants. While decellularization certainly offers advantages, this review aims to refocus attention on the unresolved matter of the host response to the extracellular matrix. Furthermore, by implicating remnant immune and inflammatory processes to bioprosthetic valve pathology, including pannus overgrowth and mineralization, the validity of a preeminent focus on decellularization, in the context of inefficient antigen and possible residual microbial remnant removal, is questioned.
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Affiliation(s)
- Paul Human
- Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town and Groote Schuur Hospital, Cape Town, South Africa.,Cardiovascular Research Unit, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Deon Bezuidenhout
- Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town and Groote Schuur Hospital, Cape Town, South Africa.,Cardiovascular Research Unit, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Elena Aikawa
- Division of Cardiovascular Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, United States
| | - Peter Zilla
- Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town and Groote Schuur Hospital, Cape Town, South Africa.,Cardiovascular Research Unit, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa.,Faculty of Health Sciences, Cape Heart Institute, University of Cape Town, Cape Town, South Africa
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8
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Aldersley T, Lawrenson J, Human P, Shaboodien G, Cupido B, Comitis G, De Decker R, Fourie B, Swanson L, Joachim A, Magadla P, Ngoepe M, Swanson L, Revell A, Ramesar R, Brooks A, Saacks N, De Koning B, Sliwa K, Anthony J, Osman A, Keavney B, Zühlke L. PROTEA, A Southern African Multicenter Congenital Heart Disease Registry and Biorepository: Rationale, Design, and Initial Results. Front Pediatr 2021; 9:763060. [PMID: 34746065 PMCID: PMC8564377 DOI: 10.3389/fped.2021.763060] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Accepted: 09/20/2021] [Indexed: 01/04/2023] Open
Abstract
Objectives: The PartneRships in cOngeniTal hEart disease (PROTEA) project aims to establish a densely phenotyped and genotyped Congenital Heart Disease (CHD) cohort for southern Africa. This will facilitate research into the epidemiology and genetic determinants of CHD in the region. This paper introduces the PROTEA project, characterizes its initial cohort, from the Western Cape Province of South Africa, and compares the proportion or "cohort-prevalences" of CHD-subtypes with international findings. Methods: PROTEA is a prospective multicenter CHD registry and biorepository. The initial cohort was recruited from seven hospitals in the Western Cape Province of South Africa from 1 April 2017 to 31 March 2019. All patients with structural CHD were eligible for inclusion. Descriptive data for the preliminary cohort are presented. In addition, cohort-prevalences (i.e., the proportion of patients within the cohort with a specific CHD-subtype) of 26 CHD-subtypes in PROTEA's pediatric cohort were compared with the cohort-prevalences of CHD-subtypes in two global birth-prevalence studies. Results: The study enrolled 1,473 participants over 2 years, median age was 1.9 (IQR 0.4-7.1) years. Predominant subtypes included ventricular septal defect (VSD) (339, 20%), atrial septal defect (ASD) (174, 11%), patent ductus arteriosus (185, 11%), atrioventricular septal defect (AVSD) (124, 7%), and tetralogy of Fallot (121, 7%). VSDs were 1.8 (95% CI, 1.6-2.0) times and ASDs 1.4 (95% CI, 1.2-1.6) times more common in global prevalence estimates than in PROTEA's pediatric cohort. AVSDs were 2.1 (95% CI, 1.7-2.5) times more common in PROTEA and pulmonary stenosis and double outlet right ventricle were also significantly more common compared to global estimates. Median maternal age at delivery was 28 (IQR 23-34) years. Eighty-two percent (347/425) of mothers used no pre-conception supplementation and 42% (105/250) used no first trimester supplements. Conclusions: The cohort-prevalence of certain mild CHD subtypes is lower than for international estimates and the cohort-prevalence of certain severe subtypes is higher. PROTEA is not a prevalence study, and these inconsistencies are unlikely the result of true differences in prevalence. However, these findings may indicate under-diagnosis of mild to moderate CHD and differences in CHD management and outcomes. This reemphasizes the need for robust CHD epidemiological research in the region.
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Affiliation(s)
- Thomas Aldersley
- Division of Paediatric Cardiology, Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
| | - John Lawrenson
- Division of Paediatric Cardiology, Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
- Division of Paediatric Cardiology, Department of Paediatrics and Child Health, University of Stellenbosch, Cape Town, South Africa
| | - Paul Human
- Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town and Groote Schuur and Red Cross Children's Hospitals, Cape Town, South Africa
| | - Gasnat Shaboodien
- Department of Medicine, Cape Heart Institute, University of Cape Town, Cape Town, South Africa
| | - Blanche Cupido
- Division of Cardiology, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - George Comitis
- Division of Paediatric Cardiology, Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
| | - Rik De Decker
- Division of Paediatric Cardiology, Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
| | - Barend Fourie
- Division of Paediatric Cardiology, Department of Paediatrics and Child Health, University of Stellenbosch, Cape Town, South Africa
| | - Lenise Swanson
- Division of Paediatric Cardiology, Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
| | - Alexia Joachim
- Division of Paediatric Cardiology, Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
| | - Phaphama Magadla
- Division of Paediatric Cardiology, Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
| | - Malebogo Ngoepe
- Department of Mechanical Engineering, University of Cape Town, Cape Town, South Africa
| | - Liam Swanson
- Department of Mechanical Engineering, University of Cape Town, Cape Town, South Africa
| | - Alistair Revell
- Department of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester, United Kingdom
| | - Raj Ramesar
- Division of Human Genetics, Department of Pathology, University of Cape Town, Cape Town, South Africa
| | - Andre Brooks
- Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town and Groote Schuur and Red Cross Children's Hospitals, Cape Town, South Africa
| | - Nicole Saacks
- Department of Medicine, Cape Heart Institute, University of Cape Town, Cape Town, South Africa
| | - Bianca De Koning
- Department of Medicine, Cape Heart Institute, University of Cape Town, Cape Town, South Africa
| | - Karen Sliwa
- Department of Medicine, Cape Heart Institute, University of Cape Town, Cape Town, South Africa
- Division of Cardiology, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - John Anthony
- Division of Maternal and Foetal Medicine, The Department of Obstetrics and Gynaecology, University of Cape Town, Cape Town, South Africa
| | - Ayesha Osman
- Division of Maternal and Foetal Medicine, The Department of Obstetrics and Gynaecology, University of Cape Town, Cape Town, South Africa
| | - Bernard Keavney
- Division of Cardiovascular Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Manchester University NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, United Kingdom
| | - Liesl Zühlke
- Division of Paediatric Cardiology, Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
- Division of Cardiology, Department of Medicine, University of Cape Town, Cape Town, South Africa
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9
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Williams DF, Bezuidenhout D, de Villiers J, Human P, Zilla P. Long-Term Stability and Biocompatibility of Pericardial Bioprosthetic Heart Valves. Front Cardiovasc Med 2021; 8:728577. [PMID: 34589529 PMCID: PMC8473620 DOI: 10.3389/fcvm.2021.728577] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2021] [Accepted: 08/19/2021] [Indexed: 01/15/2023] Open
Abstract
The use of bioprostheses for heart valve therapy has gradually evolved over several decades and both surgical and transcatheter devices are now highly successful. The rapid expansion of the transcatheter concept has clearly placed a significant onus on the need for improved production methods, particularly the pre-treatment of bovine pericardium. Two of the difficulties associated with the biocompatibility of bioprosthetic valves are the possibilities of immune responses and calcification, which have led to either catastrophic failure or slow dystrophic changes. These have been addressed by evolutionary trends in cross-linking and decellularization techniques and, over the last two decades, the improvements have resulted in somewhat greater durability. However, as the need to consider the use of bioprosthetic valves in younger patients has become an important clinical and sociological issue, the requirement for even greater longevity and safety is now paramount. This is especially true with respect to potential therapies for young people who are afflicted by rheumatic heart disease, mostly in low- to middle-income countries, for whom no clinically acceptable and cost-effective treatments currently exist. To extend longevity to this new level, it has been necessary to evaluate the mechanisms of pericardium biocompatibility, with special emphasis on the interplay between cross-linking, decellularization and anti-immunogenicity processes. These mechanisms are reviewed in this paper. On the basis of a better understanding of these mechanisms, a few alternative treatment protocols have been developed in the last few years. The most promising protocol here is based on a carefully designed combination of phases of tissue-protective decellularization with a finely-titrated cross-linking sequence. Such refined protocols offer considerable potential in the progress toward superior longevity of pericardial heart valves and introduce a scientific dimension beyond the largely disappointing 'anti-calcification' treatments of past decades.
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Affiliation(s)
- David F. Williams
- Strait Access Technologies Ltd. Pty., Cape Town, South Africa
- Wake Forest Institute of Regenerative Medicine, Wake Forest School of Medicine, Winston-Salem, NC, United States
| | - Deon Bezuidenhout
- Strait Access Technologies Ltd. Pty., Cape Town, South Africa
- Cardiovascular Research Unit, Cape Heart Institute, University of Cape Town, Cape Town, South Africa
| | | | - Paul Human
- Christiaan Barnard Department of Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa
| | - Peter Zilla
- Strait Access Technologies Ltd. Pty., Cape Town, South Africa
- Cardiovascular Research Unit, Cape Heart Institute, University of Cape Town, Cape Town, South Africa
- Christiaan Barnard Department of Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa
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de Boer C, Calder B, Blackhurst D, Marais D, Blackburn J, Steinmaurer M, Woudberg NJ, Lecour S, Lovett J, Myburgh K, Bezuidenhout D, Human P, Davies NH. Analysis of the regenerative capacity of human serum exosomes after a simple multistep separation from lipoproteins. J Tissue Eng Regen Med 2020; 15:63-77. [PMID: 33175463 DOI: 10.1002/term.3155] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 10/08/2020] [Accepted: 10/19/2020] [Indexed: 01/03/2023]
Abstract
Due to the abundance of lipoproteins in blood, it is challenging to characterize the biological functions and components of blood-derived extracellular vesicles. The aim of this study was to develop a multiple-step purification protocol to separate serum exosomes from serum proteins and lipoproteins and assess their regenerative potential. Exosomes were isolated by concentrating them in human serum using ultracentrifugation (UC), followed sequentially by density gradient (DG) UC and size exclusion chromatography (SEC). Purity and characterization were assessed by western blots, Lipoprint®, enzyme-linked immunosorbent assay, electron microscopy, mass spectrometry, and nanoparticle tracking analysis. Functionality was assessed by cell proliferation analysis and with an in vivo subcutaneous angiogenesis model. SEC alone isolated nano-sized vesicles possessing vesicle markers TSG101 and CD9, but there was a substantial presence of apolipoprotein B, predominantly derived from very-low- and intermediate-density lipoprotein particles. This was reduced to an undetectable level using the combined UC DG SEC approach. Mass spectrometry identified 224 proteins in UC DG SEC isolates relative to the 135 from SEC, with considerable increases in exosome-related proteins and reductions in lipoproteins. A consistent but limited increase in human dermal fibroblast proliferation and evidence of neovascularization enhancement were observed after exposure to UC DG SEC exosomes. An UC DG SEC purification protocol considerably improved the removal of lipoproteins during isolation of serum exosomes. The purified exosomes stimulated cell proliferation and potentially increased an in vivo angiogenic response. This multistep purification allows for more accurate identification of serum exosome functional activity and composition.
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Affiliation(s)
- Candice de Boer
- Cardiovascular Research Unit, Department of Surgery, University of Cape Town, Observatory, South Africa
| | - Bridget Calder
- Division of Chemical & Systems Biology, Department of Integrative Biomedical Sciences, Institute of Infectious Disease & Molecular Medicine, University of Cape Town, Observatory, South Africa
| | - Dee Blackhurst
- Division of Chemical Pathology, Department of Pathology, University of Cape Town, Observatory, South Africa
| | - David Marais
- Division of Chemical Pathology, Department of Pathology, University of Cape Town, Observatory, South Africa
| | - Jonathan Blackburn
- Division of Chemical & Systems Biology, Department of Integrative Biomedical Sciences, Institute of Infectious Disease & Molecular Medicine, University of Cape Town, Observatory, South Africa
| | - Martina Steinmaurer
- Cardiovascular Research Unit, Department of Surgery, University of Cape Town, Observatory, South Africa
| | - Nicholas J Woudberg
- Department of Medicine, Hatter Institute for Cardiovascular Research in Africa, University of Cape Town, Observatory, South Africa
| | - Sandrine Lecour
- Department of Medicine, Hatter Institute for Cardiovascular Research in Africa, University of Cape Town, Observatory, South Africa
| | - Jason Lovett
- Department of Physiological Sciences, Stellenbosch University, Stellenbosch, South Africa
| | - Kathy Myburgh
- Department of Physiological Sciences, Stellenbosch University, Stellenbosch, South Africa
| | - Deon Bezuidenhout
- Cardiovascular Research Unit, Department of Surgery, University of Cape Town, Observatory, South Africa
| | - Paul Human
- Cardiovascular Research Unit, Department of Surgery, University of Cape Town, Observatory, South Africa
| | - Neil H Davies
- Cardiovascular Research Unit, Department of Surgery, University of Cape Town, Observatory, South Africa
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11
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Human P, Ofoegbu C, Ilsley H, Bezuidenhout D, de Villiers J, Williams DF, Zilla P. Decellularization and engineered crosslinking: a promising dual approach towards bioprosthetic heart valve longevity. Eur J Cardiothorac Surg 2020; 58:1192-1200. [DOI: 10.1093/ejcts/ezaa257] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Revised: 05/14/2020] [Accepted: 06/14/2020] [Indexed: 12/20/2022] Open
Abstract
Abstract
OBJECTIVES
While decellularization has previously significantly improved the durability of bioprosthetic tissue, remnant immunogenicity may yet necessitate masking through crosslinking. To alleviate the fears of reintroducing the risk of calcific degeneration, we investigated the application of rationally designed crosslinking chemistry, capable of abrogating mineralization in isolation, in decellularized tissue.
METHODS
Bovine and porcine pericardium were decellularized using the standard Triton X/sodium deoxycholate/DNAse/RNAse methodology and thereafter combined incrementally with components of a four-stage high-density dialdehyde-based fixation regimen. Mechanical properties prior to, and calcium levels following, subcutaneous implantation for 6 and 10 weeks in rats were assessed.
RESULTS
Enhanced four-stage crosslinking, independent of decellularization, or decellularization followed by any of the crosslinking regimens, achieved sustained, near-elimination of tissue calcification. Decellularization additionally resulted in significantly lower tissue stiffness and higher fatigue resistance in all groups compared to their non-decellularized counterparts.
CONCLUSIONS
The dual approach of combining decellularization with enhanced crosslinking chemistry in xenogeneic pericardial tissue offers much promise in extending bioprosthetic heart valve longevity.
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Affiliation(s)
- Paul Human
- Christiaan Barnard Department of Cardiothoracic Surgery, University of Cape Town and Groote Schuur Hospital, Cape Town, South Africa
- Cardiovascular Research Unit, University of Cape Town, Cape Town, South Africa
| | - Chima Ofoegbu
- Christiaan Barnard Department of Cardiothoracic Surgery, University of Cape Town and Groote Schuur Hospital, Cape Town, South Africa
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - Helen Ilsley
- Cardiovascular Research Unit, University of Cape Town, Cape Town, South Africa
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - Deon Bezuidenhout
- Cardiovascular Research Unit, University of Cape Town, Cape Town, South Africa
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - Jandre de Villiers
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
| | - David F Williams
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
- Wake Forest School of Medicine, Winston Salem, NC, USA
| | - Peter Zilla
- Christiaan Barnard Department of Cardiothoracic Surgery, University of Cape Town and Groote Schuur Hospital, Cape Town, South Africa
- Cardiovascular Research Unit, University of Cape Town, Cape Town, South Africa
- Strait Access Technologies (SAT), University of Cape Town, Cape Town, South Africa
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12
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Swanson L, Owen B, Keshmiri A, Deyranlou A, Aldersley T, Lawrenson J, Human P, De Decker R, Fourie B, Comitis G, Engel ME, Keavney B, Zühlke L, Ngoepe M, Revell A. A Patient-Specific CFD Pipeline Using Doppler Echocardiography for Application in Coarctation of the Aorta in a Limited Resource Clinical Context. Front Bioeng Biotechnol 2020; 8:409. [PMID: 32582648 PMCID: PMC7283385 DOI: 10.3389/fbioe.2020.00409] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Accepted: 04/14/2020] [Indexed: 12/14/2022] Open
Abstract
Congenital heart disease (CHD) is the most common birth defect globally and coarctation of the aorta (CoA) is one of the commoner CHD conditions, affecting around 1/1800 live births. CoA is considered a CHD of critical severity. Unfortunately, the prognosis for a child born in a low and lower-middle income country (LLMICs) with CoA is far worse than in a high-income country. Reduced diagnostic and interventional capacities of specialists in these regions lead to delayed diagnosis and treatment, which in turn lead to more cases presenting at an advanced stage. Computational fluid dynamics (CFD) is an important tool in this context since it can provide additional diagnostic data in the form of hemodynamic parameters. It also provides an in silico framework, both to test potential procedures and to assess the risk of further complications arising post-repair. Although this concept is already in practice in high income countries, the clinical infrastructure in LLMICs can be sparse, and access to advanced imaging modalities such as phase contrast magnetic resonance imaging (PC-MRI) is limited, if not impossible. In this study, a pipeline was developed in conjunction with clinicians at the Red Cross War Memorial Children’s Hospital, Cape Town and was applied to perform a patient-specific CFD study of CoA. The pipeline uses data acquired from CT angiography and Doppler transthoracic echocardiography (both much more clinically available than MRI in LLMICs), while segmentation is conducted via SimVascular and simulation is realized using OpenFOAM. The reduction in cost through use of open-source software and the use of broadly available imaging modalities makes the methodology clinically feasible and repeatable within resource-constrained environments. The project identifies the key role of Doppler echocardiography, despite its disadvantages, as an intrinsic component of the pipeline if it is to be used routinely in LLMICs.
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Affiliation(s)
- Liam Swanson
- Department of Mechanical Engineering, University of Cape Town, Cape Town, South Africa
| | - Benjamin Owen
- Department of Mechanical, Aerospace and Civil Engineering (MACE), The University of Manchester, Manchester, United Kingdom
| | - Amir Keshmiri
- Department of Mechanical, Aerospace and Civil Engineering (MACE), The University of Manchester, Manchester, United Kingdom
| | - Amin Deyranlou
- Department of Mechanical, Aerospace and Civil Engineering (MACE), The University of Manchester, Manchester, United Kingdom
| | - Thomas Aldersley
- Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
| | - John Lawrenson
- Department of Paediatrics and Child Health, Tygerberg Hospital, Stellenbosch University and Tygerberg Hospital, Cape Town, South Africa
| | - Paul Human
- Christiaan Barnard Division of Cardiothoracic Surgery, University of Cape Town and Groote Schuur Hospital, Cape Town, South Africa
| | - Rik De Decker
- Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
| | - Barend Fourie
- Department of Paediatrics and Child Health, Tygerberg Hospital, Stellenbosch University and Tygerberg Hospital, Cape Town, South Africa
| | - George Comitis
- Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
| | - Mark E Engel
- Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - Bernard Keavney
- Division of Cardiovascular Sciences, Faculty of Biology, Medicine and Health, School of Medical Sciences, The University of Manchester, Manchester, United Kingdom.,Manchester University NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, United Kingdom
| | - Liesl Zühlke
- Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa
| | - Malebogo Ngoepe
- Department of Mechanical Engineering, University of Cape Town, Cape Town, South Africa
| | - Alistair Revell
- Department of Mechanical, Aerospace and Civil Engineering (MACE), The University of Manchester, Manchester, United Kingdom
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13
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Scherman J, Ofoegbu C, Myburgh A, Swanevelder J, van Breda B, Appa H, Human P, Williams D, Bezuidenhout D, Zilla P. Preclinical evaluation of a transcatheter aortic valve replacement system for patients with rheumatic heart disease. EUROINTERVENTION 2019; 15:e975-e982. [DOI: 10.4244/eij-d-18-01052] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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14
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Swanson L, Owen B, Revell A, Ngoepe M, Keshmiri A, Deyranlou A, Aldersley T, Lawrenson J, Human P, De Decker R, Fourie B, Comitis G, Mayosi B, Keavney B, Zuhlke L. P2427The development of a computational fluid dynamics pipeline for the study of tetralogy of Fallot and coarctation of the aorta in a developing world context. Eur Heart J 2019. [DOI: 10.1093/eurheartj/ehz748.0760] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Abstract
Background
Tetralogy of Fallot (ToF) and coarctation of the aorta (CoA) each constitute approximately 7% of congenital heart disease (CHD) births worldwide. Compared to developed countries, developing countries have a disparate level of access to prompt diagnosis and treatment for these diseases. Computational fluid dynamics (CFD) approaches implemented on routinely available non-invasive imaging data may yield low-cost improvements to the management of these patients.
Purpose
The purpose of this research is to develop a patient-specific computational pipeline that allows the modelling of blood flow in diseased arteries of patients suffering from ToF and CoA. The project aims to prove the feasible use of broadly available imaging techniques - CT angiograms (CTA) and echocardiographs (echo) - for achieving this in low-to-middle income countries. The capability of the pipeline will be demonstrated through a qualitative study of the effects of different systemic to pulmonary shunt configurations used in the palliative treatment of ToF. In addition, the effects of idealised stent configurations on the blood flow through the aorta of a patient with CoA will be studied.
Methods
A retrospective search through the hospital database was conducted to select suitable CTA data for a CoA and ToF case. Data for patient A, a five-month-old child with typical CoA, and patient B, a twelve-month-old child with typical ToF who had a central shunt in place, was found. Echo data was obtained for patient A through an investigation protocol which focused on CFD application whereas there was no echo data available for patient B. As a result, idealised volume flow rate data was implemented for patient B. Geometries for patient A and patient B were extracted and volume discretisation was implemented for grid independence testing. The Navier-Stokes governing equations for fluid flow were solved using the open source software, OpenFOAM, for the transient case where inlet volume flow rate was defined for four cardiac cycles. Figure 1 shows key features of the flow in the shunt and pulmonary branches (A), the aortic arch (B), the inlet at the ascending aorta (C) and the descending aorta (D) for the geometry extracted from the data set of patient B.
Figure 1. Key flow features of patient B
Results and discussion
We have implemented CFD models which are able to qualitatively assess the favourable or unfavourable impact of different approaches to ToF and CoA repairs on the characteristics of blood flow in the aorta and pulmonary arteries. An echo investigation protocol has been developed and successfully applied. CTA studies have been shown as feasible sources of geometry data in spite of the restriction on quality by the important requirement for low doses of radiation in paediatric patients. This project represents progress towards an advanced tool that may be broadly implemented in both well-resourced and minimally-resourced hospitals.
Acknowledgement/Funding
National Research Fund, British Heart Foundation, Newton Fund (UK MRC, South African Medical Research Council), University of Cape Town
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Affiliation(s)
- L Swanson
- University of Cape Town, Mechanical Engineering, Cape Town, South Africa
| | - B Owen
- University of Manchester, School of Mechanical, Aerospace and Civil Engineering, Manchester, United Kingdom
| | - A Revell
- University of Manchester, School of Mechanical, Aerospace and Civil Engineering, Manchester, United Kingdom
| | - M Ngoepe
- University of Cape Town, Mechanical Engineering, Cape Town, South Africa
| | - A Keshmiri
- University of Manchester, School of Mechanical, Aerospace and Civil Engineering, Manchester, United Kingdom
| | - A Deyranlou
- University of Manchester, School of Mechanical, Aerospace and Civil Engineering, Manchester, United Kingdom
| | - T Aldersley
- University of Cape Town, Department of Paediatrics & Child Health, Cape Town, South Africa
| | - J Lawrenson
- University of Cape Town, Department of Paediatrics & Child Health, Cape Town, South Africa
| | - P Human
- University of Cape Town, Cardiovascular Research Unit, Cape Town, South Africa
| | - R De Decker
- University of Cape Town, Department of Paediatrics & Child Health, Cape Town, South Africa
| | - B Fourie
- University of Stellenbosch, Department of Paediatrics & Child Health, Cape Town, South Africa
| | - G Comitis
- University of Cape Town, Department of Paediatrics & Child Health, Cape Town, South Africa
| | - B Mayosi
- University of Cape Town, Health Sciences Department, Cape Town, South Africa
| | - B Keavney
- University of Manchester, Division of Cardiovascular Science, Manchester, United Kingdom
| | - L Zuhlke
- University of Cape Town, Department of Paediatrics & Child Health, Cape Town, South Africa
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15
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Scherman J, Manganyi R, Human P, Pennel T, Brooks A, Brink J, Zilla P. Isolated mechanical aortic valve replacement in rheumatic patients in a low- to middle-income country. J Thorac Cardiovasc Surg 2019; 157:886-893. [DOI: 10.1016/j.jtcvs.2018.06.083] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2018] [Revised: 05/29/2018] [Accepted: 06/15/2018] [Indexed: 01/03/2023]
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Abstract
Objective: This study examined the relationships between appraisals of the physical environment with the subjective experience of consumers, and work satisfaction of clinicians, in Child and Adolescent Mental Health Services (CAMHS).
Design, setting, and outcome measures: A survey of clinicians, parent/guardians, and child/adolescents was conducted across eight community CAMHS in Western Australia. Respondents evaluated the waiting room and therapy rooms on a number of environmental attributes, and factor analysis was carried out to confirm that these ratings loaded on an overall appraisal of the physical environment measure. This measure was thencorrelated with self-reported subjective experience of consumers, and overall work satisfaction of staff members.
Results: Clinicians were found to be much more critical of the physical environment compared with consumers. Moderate associations were found between appraisal of the physical environment and subjective experience of consumers. A strong positive association was found between clinician appraisal of the physical environment and overall work satisfaction.
Conclusions: The present study adds to the limited existing research arguing for the important role that the physical environment can have upon both consumer and staff experience in mental health settings. The present study provides empirical evidence to justify steps being taken to enhance the physical environment in mental health clinics. The inter-relationship between physical environment attributes suggests there is potential for managers to improve the overall perception of clinic space via relatively small actions (e.g., adding a nice piece of artwork).
Abbreviations: CAMHS – Child and Adolescent Mental Health Services.
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Human P, Ilsley H, Roberson C, Grovender E, Van Antwerp B, Fogt E, Zilla P. Assessment of the Immunogenicity of Mechanically Induced Interferon Aggregates in a Transgenic Mouse Model. J Pharm Sci 2015; 104:722-30. [DOI: 10.1002/jps.24292] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Revised: 10/27/2014] [Accepted: 10/29/2014] [Indexed: 11/09/2022]
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19
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Moodley L, Franz T, Human P, Wolf MF, Bezuidenhout D, Scherman J, Zilla P. Protective constriction of coronary vein grafts with knitted nitinol. Eur J Cardiothorac Surg 2013; 44:64-71. [PMID: 23295444 DOI: 10.1093/ejcts/ezs670] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
OBJECTIVES Different flow patterns and shear forces were shown to cause significantly more luminal narrowing and neointimal tissue proliferation in coronary than in infrainguinal vein grafts. As constrictive external mesh support of vein grafts led to the complete suppression of intimal hyperplasia (IH) in infrainguinal grafts, we investigated whether mesh constriction is equally effective in the coronary position. METHODS Eighteen senescent Chacma baboons (28.8 ± 3.6 kg) received aorto-coronary bypass grafts to the left anterior descending artery (LAD). Three groups of saphenous vein grafts were compared: untreated controls (CO); fibrin sealant-sprayed controls (CO + FS) and nitinol mesh-constricted grafts (ME + FS). Meshes consisted of pulse-compliant, knitted nitinol (eight needles; 50 μm wire thickness; 3.4 mm resting inner diameter, ID) spray attached to the vein grafts with FS. After 180 days of implantation, luminal dimensions and IH were analysed using post-explant angiography and macroscopic and histological image analysis. RESULTS At implantation, the calibre mismatch between control grafts and the LAD expressed as cross-sectional quotient (Qc) was pronounced [Qc = 0.21 ± 0.07 (CO) and 0.18 ± 0.05 (CO + FS)]. Mesh constriction resulted in a 29 ± 7% reduction of the outer diameter of the vein grafts from 5.23 ± 0.51 to 3.68 ± 0 mm, significantly reducing the calibre discrepancy to a Qc of 0.41 ± 0.17 (P < 0.02). After 6 months of implantation, explant angiography showed distinct luminal irregularities in control grafts (ID difference between widest and narrowest segment 74 ± 45%), while diameter variations were mild in mesh-constricted grafts. In all control grafts, thick neointimal tissue was present [600 ± 63 μm (CO); 627 ± 204 μm (CO + FS)] as opposed to thin, eccentric layers of 249 ± 83 μm in mesh-constricted grafts (ME + FS; P < 0.002). The total wall thickness had increased by 363 ± 39% (P < 0.00001) in CO and 312 ± 61% (P < 0.00001) in CO + FS vs 82 ± 61% in ME + FS (P < 0.007). CONCLUSIONS In a senescent non-human primate model for coronary artery bypass grafts, constrictive, external mesh support of saphenous veins with knitted nitinol prevented focal, irregular graft narrowing and suppressed neointimal tissue proliferation by a factor of 2.5. The lower degree of suppression of IH compared with previous infrainguinal grafts coincided with a lesser reduction of calibre mismatch in the coronary grafts.
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Affiliation(s)
- Loven Moodley
- Chris Barnard Department of Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa
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Zilla P, Moodley L, Scherman J, Krynauw H, Kortsmit J, Human P, Wolf MF, Franz T. Remodeling leads to distinctly more intimal hyperplasia in coronary than in infrainguinal vein grafts. J Vasc Surg 2012; 55:1734-41. [DOI: 10.1016/j.jvs.2011.11.057] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2011] [Revised: 11/02/2011] [Accepted: 11/09/2011] [Indexed: 11/25/2022]
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Franz T, Human P, Dobner S, Reddy BD, Black M, Ilsley H, Wolf MF, Bezuidenhout D, Moodley L, Zilla P. Tailored sizes of constrictive external vein meshes for coronary artery bypass surgery. Biomaterials 2010; 31:9301-9. [DOI: 10.1016/j.biomaterials.2010.08.054] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Accepted: 08/24/2010] [Indexed: 10/19/2022]
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Zilla P, Wolf M, Rafiee N, Moodley L, Bezuidenhout D, Black M, Human P, Franz T. Utilization of shape memory in external vein-graft meshes allows extreme diameter constriction for suppressing intimal hyperplasia: A non-human primate study. J Vasc Surg 2009; 49:1532-42. [DOI: 10.1016/j.jvs.2009.01.068] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2008] [Revised: 01/22/2009] [Accepted: 01/31/2009] [Indexed: 11/25/2022]
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Human P, Franz T, Scherman J, Moodley L, Zilla P. Dimensional analysis of human saphenous vein grafts: Implications for external mesh support. J Thorac Cardiovasc Surg 2009; 137:1101-8. [PMID: 19379974 DOI: 10.1016/j.jtcvs.2008.10.040] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Revised: 09/05/2008] [Accepted: 10/03/2008] [Indexed: 11/24/2022]
Abstract
OBJECTIVE Constrictive external mesh support of vein grafts was shown to mitigate intimal hyperplasia in animal experiments. To determine the degree of constriction required for the elimination of dimensional irregularities in clinically used vein grafts, a detailed anatomic study of human saphenous veins was conducted. METHODS In 200 consecutive patients having coronary artery bypass grafting, harvested saphenous veins (length 34.4 +/- 10.8 cm) were analyzed regarding diameter irregularities, side branch distribution, and microstructure. RESULTS The mean outer diameter of surgically distended saphenous veins was 4.2 +/- 0.6 mm (men, 4.3 +/- 0.6 mm vs women, 3.9 +/- 0.5 mm; P < .0001). Although the outer diameter significantly decreased over the initial 18 cm (-7.6%; P < .0001), the overall increase between malleolus and thigh was not significant (+11.2%). Smaller-diameter veins (<3.5 mm) had more pronounced diameter fluctuations than larger veins (31.8% +/- 11.0% vs 21.2% +/- 8.8%; P < .0001), with more than 71% of all veins showing caliber changes of more than 20%. There was 1 side branch every 5.4 +/- 4.3 cm, with a significantly higher incidence between 20 and 32 cm from the malleolus (P < .0001 to distal, P < .0004 to proximal). Generally, women had more side branches than men (0.30 +/- 0.15 cm(-1) vs 0.25 +/- 0.12 cm(-1); P = .0190). Thick-walled veins (565.7 +/- 138.4 mum) had a significantly higher number of large side branches (P < .0001), and thin-walled veins (398.7 +/- 123.2 mum) had significantly more small side branches (P < .0001). Pronounced intimal thickening ("cushions") was found in 28% of vessels (119.8 +/- 28.0 mum vs 40.1 +/- 18.2 mum; P < .0001). CONCLUSION Although the preferential location of side branches may be addressed by the deliberate discarding of infragenicular vein segments, a diameter constriction of 27% on average would eliminate diameter irregularities in 98% of vein grafts.
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Affiliation(s)
- Paul Human
- Christiaan Barnard Department of Cardiothoracic Surgery, University of Cape Town, Observatory, South Africa
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Zilla P, Brink J, Human P, Bezuidenhout D. Prosthetic heart valves: Catering for the few. Biomaterials 2008; 29:385-406. [DOI: 10.1016/j.biomaterials.2007.09.033] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Accepted: 09/23/2007] [Indexed: 01/17/2023]
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Abstract
In humans, prosthetic vascular grafts remain largely without an endothelium, even after decades of implantation. While this shortcoming does not affect the clinical performance of large bore prostheses in aortic or iliac position, it contributes significantly to the high failure rate of small- to medium-sized grafts (SMGs). For decades intensive but largely futile research efforts have been under way to address this issue. In spite of the abundance of previous studies, a broad analysis of biological events dominating the incorporation of vascular grafts was hitherto lacking. By focusing on the three main contemporary graft types, expanded polytetrafluoroethylene (ePTFE), Dacron and Polyurethane (PU), accumulated clinical and experimental experience of almost half a century was available. The main outcome of this broad analysis-supported by our own experience in a senescent non-human primate model-was twofold: Firstly, inappropriate animal models, which addressed scientific questions that missed the point of clinical relevance, were largely used. This led to a situation where the vast majority of investigators unintentionally studied transanastomotic rather than transmural or blood-borne endothelialization. Given the fact that in patients transanastomotic endothelialization (TAE) covers only the immediate perianastomotic region of sometimes very long prostheses, TAE is rather irrelevant in the clinical context. Secondly, transmural endothelialization seems to have a time window of opportunity before a build-up of an adverse microenvironment. In selecting animal models that prematurely terminate this build-up through the early presence of an endothelium, the most significant 'impairment factor' for physiological tissue regeneration in vascular grafts remained ignored. By providing insight into mechanisms and experimental designs which obscured the purpose and scope of several decades of vascular graft studies, future research may better address clinical relevance.
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Affiliation(s)
- Peter Zilla
- Christian Barnard Department of Cardiothoracic Surgery/Cardiovascular Research Unit, University of Cape Town Medical School, Cape Town, South Africa.
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Everaerts F, Gillissen M, Torrianni M, Zilla P, Human P, Hendriks M, Feijen J. Reduction of calcification of carbodiimide-processed heart valve tissue by prior blocking of amine groups with monoaldehydes. J Heart Valve Dis 2006; 15:269-77. [PMID: 16607911] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
BACKGROUND AND AIM OF THE STUDY Failure of implanted bioprostheses due to calcification is a commonly occurring phenomenon. In order to prevent calcification, many alternative cross-linking methods to glutaraldehyde (GA) have been developed and evaluated. METHODS In a novel approach an improved carbodiimide (EDC) cross-linking method that comprises a two-step process was developed. First, the available amine groups in (tissue) collagen were blocked with a monoaldehyde, followed by an EDC-activated cross-linking reaction of the carboxyl groups in the tissue with a poly (propylene glycol) bis 2-(amino-propyl) ether (Jeffamine). RESULTS Samples processed via this method have shown a significantly reduced calcification in a subdermal juvenile rat model compared to samples with standard GA treatment. In the present study, heart valve tissue was blocked with various monoaldehydes, followed by reaction with Jeffamine using carbodiimide cross-linking chemistry. Leaflet calcification was almost eliminated using different aldehydes, whereas wall calcification was maximally 95% reduced when propionaldehyde was used as blocking agent, as compared to a carbodiimide cross-linked control without Jeffamine and blocked amine groups. CONCLUSION Amine blocking and cross-linking technology appears promising in the design of the next generation of tissue valves. Calcification was significantly reduced compared to GA cross-linking. The mechanistic insight of decreased wall calcification is still unknown, and research investigations are ongoing.
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Rippstein P, Black MK, Boivin M, Veinot JP, Ma X, Chen YX, Human P, Zilla P, O'Brien ER. Comparison of processing and sectioning methodologies for arteries containing metallic stents. J Histochem Cytochem 2006; 54:673-81. [PMID: 16714423 DOI: 10.1369/jhc.5a6824.2006] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The histological study of arteries with implanted metallic scaffolding devices, known as stents, remains a technical challenge. Given that the arterial response to stent implantation can sometimes lead to adverse outcomes, including the re-accumulation of tissue mass within the stent (or in-stent restenosis), overcoming these technical challenges is a priority for the advancement of research and development in this important clinical field. Essentially, the task is to section the stent-tissue interface with the least amount of disruption of tissue and cellular morphology. Although many methacrylate resin methodologies are successfully applied toward the study of endovascular stents by a variety of research laboratories, the exact formulations, as well as subsequent processing and sectioning methodology, remain largely coveted. In this paper, we describe in detail a methyl methacrylate resin-embedding methodology that can successfully be applied to tungsten carbide blade, as well as saw and grinding sectioning methods and transmission electron microscopy. In addition, we present a comparison of the two sectioning methodologies in terms of their effectiveness with regard to morphological, histochemical, and immunohistochemical analyses. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.
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Affiliation(s)
- Peter Rippstein
- ART, MLT, Core Pathology Laboratory, University of Ottawa Heart Institute, 40 Ruskin Street, Rm H2102, Ottawa, Ontario, Canada K1Y 4W7.
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Zilla P, Bezuidenhout D, Torrianni M, Hendriks M, Human P. Diamine-extended glutaraldehyde- and carbodiimide crosslinks act synergistically in mitigating bioprosthetic aortic wall calcification. J Heart Valve Dis 2005; 14:538-45. [PMID: 16116882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
BACKGROUND AND AIM OF THE STUDY The extension of glutaraldehyde (GA) crosslinks with diamine bridges was shown previously to reduce bioprosthetic heart valve calcification to a significant degree. The aim of the present study was to investigate whether the additional crosslinking of functional carboxyl groups could augment this anticalcific effect at the low glutaraldehyde concentrations typically used in commercial heart valve production. METHODS Entire aortic roots of medium-sized pigs were fixed after 48 h of cold storage. Crosslinking of amino-functional groups was achieved either by GA fixation alone (0.2% or 0.7%) or with an interim treatment with the diamine L-lysine (25, 50 or 100 mM; 37 degrees C; 2 days). Carboxyl groups were activated with carbodiimide (N'-{3-dimethylaminopropyl}-N-ethyl carbodiimide hydrochloride (EDC), 240 mM) and crosslinked with an oligomeric diamine (polypropylene glycol-bis-aminopropyl ether (Jeffamine), 60 mM, 230D). By permutation of treatments and combinations thereof, a total of 17 groups was compared. Aortic wall discs (12 mm diameter) were implanted subcutaneously into seven-week-old Long-Evans rats for 60 days. Tissue calcification was determined by histology and atomic absorption spectrophotometry. RESULTS There was no significant difference in tissue calcification if either GA or carbodiimide fixation was used alone. Equally, the combined crosslinking with GA and EDC/Jeffamine did not achieve a mitigation of tissue calcification below levels seen in at least one of the two treatments alone. When commercial GA fixation was mildly diamine-enhanced with L-lysine (25 mM), additional EDC/Jeffamine crosslinking of carboxyl groups resulted in a distinct additive effect in both 0.2% (-31%; p < 0.0002) and 0.7% (-36%; p = 0.0073) GA-fixed tissue. Relative to conventional GA fixation, this combination mitigated aortic wall calcification by 43% (p < 0.0001) and 34% (p = 0.0014) in 0.2% and 0.7% GA-fixed tissue, respectively. An increase in L-lysine concentration to 100 mM further reduced calcification of 0.7% GA-fixed tissue (18.5%; p = 0.016), but had no additional effect on 0.2% GA-fixed tissue (0.6%; p = 0.463). CONCLUSION A distinct reduction in bioprosthetic aortic wall calcification can be achieved by combining diamine-extended conventional GA fixation with a diamine-extended carbodiimide based crosslinking step.
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Affiliation(s)
- Peter Zilla
- Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town, South Africa.
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Zilla P, Bezuidenhout D, Human P. Carbodiimide Treatment Dramatically Potentiates the Anticalcific Effect of Alpha-Amino Oleic Acid on Glutaraldehyde-Fixed Aortic Wall Tissue. Ann Thorac Surg 2005; 79:905-10. [PMID: 15734403 DOI: 10.1016/j.athoracsur.2003.12.026] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 12/10/2003] [Indexed: 11/22/2022]
Abstract
BACKGROUND Bifunctional amines were previously found to act as bridging molecules between the terminal ends of incomplete glutaraldehyde (GA) cross-links. The additional cross-links thus formed between -NH2 groups of tissue were seen to significantly inhibit bioprosthetic calcification. In the current study, the potential ability of alpha-amino oleic acid (AOA) to act as a bridging molecule between -NH2- and COOH-dependent cross-links was hypothesized to similarly augment the anticalcification effect of the AOA molecule. METHODS Porcine aortic wall tissue from Medtronic Freestyle valve bioprostheses incorporating the AOA anticalcification process additionally underwent carboxyl-group cross-linking with Jeffamine (poly[propylene glyco]-bis-[aminopropyl ether]) using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). Tissue was subdermally implanted into 5-week-old Long-Evans rats for 60 days. Standard 0.2% GA-fixed tissue served as a control. To further assess the impact of storage solution on AOA tissue, samples were either stored in GA (0.2%GA) or EDC (25 mmol/L carbodiimide) before implantation. Tissue calcification was assessed by atomic absorption spectroscopy and histochemical staining. RESULTS Aldehyde end-capping with AOA achieved only a modest reduction of calcification in GA-treated aortic wall tissue (-20.0%; p < 0.05). Replacing GA with EDC as a storage solution led to a further 32.4% (p < 0.01) mitigation of calcification in Freestyle tissue. Incorporating an intermediate EDC/Jeffamine cross-linking step achieved a distinct additional reduction of calcification by 40.4% (p < 0.05). Overall, aortic wall calcification was 59.7% (p < 0.0001) lower if commercial Freestyle tissue underwent an additional EDC/Jeffamine cross-linking step and subsequent storage in EDC. Relative to control GA-fixed tissue, this represented a 67.8% (p < 0.0001) reduction. Incorporation of AOA was essential for the beneficial effect of the additional EDC/Jeffamine cross-linking step. CONCLUSIONS Potentially utilizing both the amino- and the carboxyl moieties of AOA for tissue binding dramatically reduces aortic wall calcification of GA-fixed tissue.
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Affiliation(s)
- Peter Zilla
- Chris Barnard Division of Cardiothoracic Surgery, Cape Heart Center, University of Cape Town, Cape Town, South Africa.
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Fittkau MH, Zilla P, Bezuidenhout D, Lutolf MP, Human P, Hubbell JA, Davies N. The selective modulation of endothelial cell mobility on RGD peptide containing surfaces by YIGSR peptides. Biomaterials 2005; 26:167-74. [PMID: 15207463 DOI: 10.1016/j.biomaterials.2004.02.012] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2003] [Accepted: 02/04/2004] [Indexed: 10/26/2022]
Abstract
The ability of the biomimetic peptides YIGSR, PHSRN and RGD to selectively affect adhesion and migration of human microvascular endothelial cells (MVEC) and vascular smooth muscle cells (HVSMC) was evaluated. Cell mobility was quantified by time-lapse video microscopy of single cells migrating on peptide modified surfaces. Polyethylene glycol (PEG) hydrogels modified with YIGSR or PHSRN allowed only limited adhesion and no spreading of MVEC and HVSMC. However, when these peptides were individually combined with the strong cell binding peptide RGD in PEG hydrogels, the YIGSR peptide was found to selectively enhance the migration of MVEC by 25% over that of MVEC on RGD alone (p<0.05). No corresponding effect was observed for HVSMC. This suggests that the desired response of specific cell types to tissue engineering scaffolds could be optimized through a combinatory approach to the use of biomimetic peptides.
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Affiliation(s)
- M H Fittkau
- Cardiovascular Research Unit, Christian Barnard Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town, Anzio Road, 7925 Observatory, Cape Town, South Africa
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Abstract
More than 250,000 bioprosthetic heart valves are being implanted annually. Although the majority of recipients are elderly developed-world patients, the most urgent need for tissue valves is in younger patients, where rapid degeneration of contemporary prostheses remains a serious obstacle. After decades of empirical and mostly futile attempts to extend the longevity of tissue valve prostheses, new insights and solutions are on the horizon. Aetiologically, a shift of focus from mineralization to immune responses and inflammation emerges. On the development side, new engineering approaches to both selective extraction of tissue components and cross-links are increasingly defining the new direction. In order to dramatically improve the performance of bioprosthetic heart valves, these new developments need to lead to a broad consensus for a paradigm shift in a hitherto rather stagnant field of medical research.
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Affiliation(s)
- Peter Zilla
- Christiaan Barnard Department of Cardiothoracic Surgery, University of Cape Town Medical School and Groote Schuur Hospital, Christian Barnard Building, Anzio Road, 7925 Observatory/Cape Town, South Africa.
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Trantina-Yates AE, Human P, Zilla P. Detoxification on top of enhanced, diamine-extended glutaraldehyde fixation significantly reduces bioprosthetic root calcification in the sheep model. J Heart Valve Dis 2003; 12:93-100; discussion 100-1. [PMID: 12578343] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/28/2023]
Abstract
BACKGROUND AND AIM OF THE STUDY Increased concentrations of glutaraldehyde (GA), diamine-extension (DA) of crosslinks and subsequent extraction of excess GA all reduce bioprosthetic calcification in the subdermal rat model. The study aim was to demonstrate the combined effect of all three treatments in a circulatory sheep model. METHODS Two fixation treatments were used for GA detoxification (urazole in acetate buffer, 0.1 M; pH 4.5; 37 degrees C; 7 days): (i) conventional 0.2% GA fixation (4 degrees C; 7 days); and (ii) enhanced 3.0% GA fixation (4 degrees C; 2 days, followed by a DA interim step; 100 mM L-lysine; 37 degrees C; 2 days, followed by GA; 3.0%; 37 degrees C; 5 days). Entire porcine root prostheses were implanted in the distal aortic arch of young sheep for 12 weeks (n = 5 per group). Non-detoxified 0.2% GA-treated roots served as controls (n = 5). Calcium analysis was based on atomic absorption spectrophotometry; morphology was assessed using light and transmission electron microscopy. RESULTS Detoxification alone resulted in an 83% reduction of leaflet calcification (p = 0.086), but achieved only 23% (p = 0.145) and 12% (p = 0.362) mitigation of calcification in aortic wall and sinus tissue, respectively. When combined with DA-enhanced 3% GA fixation, detoxification led to a 95% reduction in leaflet calcification (p = 0.057), followed by 79% in sinus (p = 0.003) and 79% in aortic wall tissue (p = 0.0003). Morphologically, detoxification primarily affected leaflets and the subadventitial layer of aortic wall tissue, whereas enhanced fixation seemed to affect all structures. CONCLUSION It was shown in a circulatory sheep model that a combination of DA-enhanced fixation with an extraction process of excess GA leads to a distinct mitigation of leaflet and aortic wall calcification.
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Affiliation(s)
- Ameli E Trantina-Yates
- Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town, South Africa
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Bracher M, Simionescu D, Simionescu A, Davies N, Human P, Zilla P. Matrix metalloproteinases and tissue valve degeneration. J Long Term Eff Med Implants 2002; 11:221-30. [PMID: 11921665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
Bioprosthetic heart valves have been used as replacements for diseased heart valves for over 30 years. More than 50% of bioprosthetic valves fail within 15 years because of structural deterioration. The role of proteolytic degradation, with particular reference to the matrix metalloproteinases (MMPs) in the degeneration of aortic bioprostheses, is appraised in this minireview. It is clear that both the intrinsic and host-derived proteolytic activities present in heart-valve bioprostheses may combine with mechanical stress to bring about valve failure.
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Affiliation(s)
- M Bracher
- Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town Medical School, Cape Town, South Africa
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Human P, Zilla P. Inflammatory and immune processes: the neglected villain of bioprosthetic degeneration? J Long Term Eff Med Implants 2002; 11:199-220. [PMID: 11921664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
In an attempt to avoid the destructive process of bioprosthetic heart-valve calcification associated with the use of glutaraldehyde, valves are today prepared using low concentrations of the crosslinking reagent. In this review, we summarize our findings and those of others that confirm that the immunogenicity of such tissue is not sufficiently masked and that a defined humoral response is indeed mounted against a repertoire of antigens unrelated to those associated with vascularized and non-cross-linked xenograft organs. We demonstrate the need for increased cross-linking of tissue to satisfactorily mitigate that response; furthermore, we examine the impact of increased cross-link density on the macrophage as antigen presenting cell with respect to its involvement in both tissue erosion and pannus overgrowth. Finally we present evidence for a role of circulating antibodies in bioprosthesis calcification.
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Affiliation(s)
- P Human
- Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town Medical School, Cape Town, South Africa
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Abstract
BACKGROUND Increasing concentrations of glutaraldehyde (GA) lead to a decreased rather than increased calcification of bioprosthetic aortic wall tissue. This study determined to what extent the benefit of better cross-linking is masked by the intrinsic propensity of GA towards calcification. MATERIALS AND METHODS Porcine aortic roots were immediately fixed at the abattoir at three different concentrations of GA (0.2%, 1.0%, and 3.0% for 1 week at 4 degrees C). Subsequently, roots underwent a GA extraction process using high volumes of Urazole solution (acetic acid buffer, pH 4.5, 37 degrees C, 1 week) followed by NaBH4 reduction (2 days, 37 degrees C). Roots were implanted in the distal aortic arch of young sheep for 6 weeks and 6 months. Calcium analysis was quantitatively done by atomic absorption spectrophotometry and qualitatively assessed by light microscopy on Von Kossa stains. RESULTS There was a distinct anticalcification effect of GA detoxification after 6 weeks (56.8% to 97.9%; 95% confidence interval [CI]), which stabilized on a more moderate level after 6 months of implantation (19.1% to 31.6%; 95% CI). The most pronounced effect of GA extraction was seen in 0.2% fixed tissue, where aortic wall calcification was mitigated by 97% and 32% after 6 weeks and 6 months, respectively. Mitigation of aortic wall calcification was 71% (6 weeks) and 21% (6 months) in the 3.0% GA group. The combined effect of higher cross-link density and detoxification achieved an 82% (6 weeks) and 48% (6 months) reduction of calcium levels in the 3.0% GA group. In long-term implants (6 months), detoxification alone on top of standard 0.2% GA fixation was as effective (from 174.1 +/- 11.9 microg/mg without detoxification to 119.3 +/- 19.3 microg/mg with detoxification) as 3.0% fixation (114.8 +/- 10.0 microg/mg without detoxification to 91.3 +/- 11.5 microg/mg with detoxification). CONCLUSION We were able to determine in the circulatory sheep model to what degree the intrinsic procalcific effect of GA counteracts the protective effect of higher cross-link density. Our study also established that the effect of detoxification is particularly pronounced in commercial low-grade fixation.
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Affiliation(s)
- P Zilla
- Department of Cardiothoracic Surgery, Cape Heart Center, University of Cape Town, South Africa.
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Human P, Weissenstein C, Trantina A, Zilla P. Fixation-related autolysis and bioprosthetic aortic wall calcification. J Heart Valve Dis 2001; 10:656-65. [PMID: 11603606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Abstract
BACKGROUND AND AIM OF THE STUDY It has been established previously that immediate fixation and increased glutaraldehyde (GA) concentrations are required to prevent severe autolytic tissue damage during bioprosthetic aortic root production. The study aim was to verify that structure-preserving fixation also reduces aortic wall calcification. METHODS Porcine aortic roots were fixed either instantly or after being kept on ice for 48 h (phosphate-buffered saline, PBS). Two concentrations of GA (0.2% and 3.0%) were chosen (4 degrees C, seven days, PBS). Discs of aortic wall tissue (1.2 cm diameter) were implanted subcutaneously in rats for 60 days (n = 10 per group), while aortic roots were implanted in the distal aortic arch of sheep for six weeks (n = 3 per group) and six months (n = 4 per group). Calcification was assessed by atomic absorption spectrophotometry and light microscopy. Fixation-related tissue damage was determined by transmission electron microscopy, and correlated with calcification. RESULTS No significant difference in calcification was found between immediate and delayed fixation if tissue was fixed with 0.2% GA. In the 3.0% GA group, both animal models showed a significantly lower level of calcification if tissue was immediately fixed. In the subcutaneous rat model, immediate fixation reduced calcification by 26% (p <0.0001). In the circulatory sheep model immediate fixation did not affect calcification in the short-term six-week implants, but markedly lowered it by 37% (p = 0.035) after six months. Ultrastructurally, there was a significant correlation between membrane damage, vacuolization and vesicle shedding on the one hand, and calcification on the other. CONCLUSION Coincidental fixation-related ultrastructural damage and increased calcification was demonstrated in bioprosthetic aortic wall tissue.
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Affiliation(s)
- P Human
- Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town Medical School, South Africa
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Trantina-Yates AE, Human P, Bracher M, Zilla P. Mitigation of bioprosthetic heart valve degeneration through biocompatibility: in vitro versus spontaneous endothelialization. Biomaterials 2001; 22:1837-46. [PMID: 11396888 DOI: 10.1016/s0142-9612(00)00365-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
BACKGROUND Glutaraldehyde-related cytotoxicity and transanastomotic ingrowth inhibition prevent the spontaneous endothelialization of bioprosthetic heart valves. In order to evaluate the ability of improved biocompatibility to reduce tissue degeneration, conventionally fixed aortic root prostheses were both glutaraldehyde-detoxified and in vitro endothelialized. METHODS Entire aortic roots were fixed in 0.2% glutaraldehyde (GA) (control group) and either detoxified in acetic acid-buffered urazole (0.1 M) or detoxified and in vitro lined with cultured, autologousjugular vein endothelial cells. The valved roots were inserted in the distal aortic arch of 15 juvenile Merino sheep for a period of 12 weeks. Upon explant, leaflets, sinuses and aortic wall of the prostheses were analysed by SEM to assess the surface endothelium, histologically regarding tissue inflammation, and by atomic absorption spectrophotometry to determine the content of tissue calcium. RESULTS There was no endothelium on control grafts, except for a short anastomotic pannus. The detoxified group showed an incomplete patchy endothelium on the aortic wall but hardly any on the leaflets, whereas, the in vitro lined group had aortic wall, sinuses and most of the leaflets confluently endothelialized. Tissue inflammation was prominent in the control group and least expressed in the endothelialized group (p < 0.05). Detoxification significantly reduced leaflet calcification. In the aortic wall, both detoxification and endothelial lining were required to significantly mitigate calcification. CONCLUSION In the 12 week circulatory sheep model, the calcium mitigating effect of detoxification was more pronounced than that of in vitro endothelialization. Nevertheless, there was a distinct overall benefit if detoxification was combined with endothelialization.
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Affiliation(s)
- A E Trantina-Yates
- Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town Medical School, South Africa
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Human P, Zilla P. The possible role of immune responses in bioprosthetic heart valve failure. J Heart Valve Dis 2001; 10:460-6. [PMID: 11499591] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Affiliation(s)
- P Human
- Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town Medical School, South Africa
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Zilla P, Bezuidenhout D, Weissenstein C, van der Walt A, Human P. Diamine extension of glutaraldehyde crosslinks mitigates bioprosthetic aortic wall calcification in the sheep model. J Biomed Mater Res 2001; 56:56-64. [PMID: 11309791 DOI: 10.1002/1097-4636(200107)56:1<56::aid-jbm1068>3.0.co;2-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We previously have been able to show that fixation at increasing concentrations of glutaraldehyde (GA) leads to mitigated rather than facilitated tissue calcification. The purpose of the present study was to introduce additional crosslinks and provide evidence that crosslink density may be an underlying inhibitory principle. Entire aortic roots were chosen to verify the concept on the challenging aortic wall tissue. Porcine aortic roots were crosslinked with 0.2% GA, 3%GA, and 3% GA containing an interim step that introduced diamine bridges. Crosslink efficiency was determined on the basis of shrinkage temperature (SrT degrees ), resistance to protease digestion (RPD), residual amine analysis (RA), and tensile modulus (E(10)). Calcium levels, calcification patterns, and inflammation were assessed after 6 and 24 weeks of implantation in a sheep circulatory model. Crosslink efficiency in aortic wall tissue was moderately affected by increasing the fixative concentration from 0.2% GA to 3% GA (SrT degrees from 85.7 degrees +/- 0.3 degrees to 87.5 degrees +/- 0.3 degrees C, p < 0.002; RPD from 24.2 +/- 1.2 to 29.1 +/- 0.7%, p < 0.003; RA from 0.069 +/- 0.004 to 0.058 +/- 0.003 micromol/mg, p < 0.03, and E(10) from 1.9 +/- 0.11 to 2.94 +/- 0.34 MPa, p < 0.01), but it was distinctly enhanced when diamine bridges were introduced (SrT degrees from 87.5 degrees +/- 0.3 degrees to 93.4 degrees +/- 0.3 degrees C, p << 0.0001; RPD from 29.1 +/- 0.7 to 68.4 +/- 1.8%, p << 0.0001; and E(10) from 2.94 +/- 0.34 to 6.80 +/- 0.61 MPa, p < 0.0003). Aortic wall calcification was reduced significantly by increasing the GA concentration from 0.2 to 3% [37.8%, p = 0.076 (6 weeks) and 34.0%, p = 0.008 (24 weeks)] and further reduced by the introduction of additional diamine [84.0%, p = 0.006 (6 weeks) and 29.8%, p = 0.037 (24 weeks)]. The combined effect of increased GA concentration plus an interim diamine step on aortic wall tissue resulted in a 90% and 53.7% reduction of calcification after 6 weeks and 24 weeks, respectively. The correlation coefficients between calcification and SrT degrees, RDP, and E(10) was -0.9767, -0.9460, and -0.9740, respectively (6 weeks). The inflammatory host reaction regularly found in 0.2% fixed tissue was practically abolished through the introduction of diamine bridges. Our study demonstrated a distinct correlation between the mitigation of aortic wall calcification and three parameters used to assess crosslink density.
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Affiliation(s)
- P Zilla
- Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town Medical School, SAMIOT Building, Anzio Road, ZA 7925 Observatory, Cape Town, South Africa.
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Abstract
BACKGROUND The mild inflammatory response against stented bioprosthetic heart valves in the sheep model is often opposed by a more distinct response in failing human implants. With the emergence of stentless root prostheses with their significantly larger proportion of tissue interacting with the immune system of the host, a more relevant animal model than the sheep may be needed. METHODS Valved, porcine aortic roots of 5 cm length were fixed in 0.2% glutaraldehyde and implanted in the upper descending aorta of Merino sheep (n = 5; 43+/-3 kg) and Chacma baboons (n = 5; 17+/-3 kg). After 6 weeks of tissue calcification, pannus outgrowth and inflammation were assessed by atomic absorption spectrophotometry, histologic damage scoring (0 to 3), image analysis, and transmission electron microscopy. RESULTS The main difference between the two animal models was in aortic wall calcification (64.8+/-39.8 microg/mg in the sheep model versus 4.1+/-5.9 microg/mg in the primate model; p > 0.005). In both models, leaflet calcification was negligible (2.6+/-2.4 microg/mg in the sheep versus 2.5+/-1.9 microg/mg in the primate), and the overall extent of inflammation was comparable (1.2+/-0.8 versus 0.98+/-0.7; p = 0.18 in the sheep and the primate, respectively). Qualitatively, the sheep demonstrated a macrophage-dominated reaction whereas the inflammatory demarcation often resembled a granulocyte-dominated xenograft response in the primate. Pannus outgrowth was comparable in length (8.4+/-2.3 mm versus 9.1+/-4.3 mm proximally and 7.1+/-3.4 mm versus 7.4+/-5.1 mm distally, in the sheep and baboon, respectively; p > 0.05). CONCLUSIONS Our results confirm the sheep as a significantly stronger calcification model for stentless aortic heart valves than the primate. Remaining antigenicity of porcine tissue as a result of incomplete cross-linking, however, elicits a distinctly stronger xenograft-type reaction in the primate model.
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Affiliation(s)
- A Trantina-Yates
- Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town Medical School, South Africa
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Abstract
BACKGROUND The role of an immune response in the failure of bioprosthetic heart valves is poorly understood and disregarded by many. To elucidate the nature of the immune response to glutaraldehyde-treated tissue and the possible role of graft-specific antibody in graft mineralization, we performed immune-calcification studies in the rabbit and correlated those results with the analysis of specific antibodies. METHODS Aortic wall buttons (6 mm) were punched from porcine aortic wall tissue fixed with 0.2% glutaraldehyde and detoxified with urazole and then subsequently perforated under sterile conditions. The perforated buttons were then incubated with either immune serum prepared by immunization of New Zealand White rabbits (n = 5) with Freund's incomplete adjuvant emulsions of tissue homogenates of similarly treated aortic wall tissue, or incubated with the corresponding control preimmune sera obtained before immunization of the same animals. The tissue was then implanted subdermally on the back of unrelated New Zealand White rabbits (n = 8) for a period of 3 weeks. After the buttons were explanted, tissue calcium levels were determined by atomic absorption spectroscopy. RESULTS Tissue calcium was increased in all five immune serum-treated replicates (range, 61.8% to 431.2%; mean, 225.9%+/-73.2%) when compared with control samples treated with preimmune sera. Overall, the mean calcium level was significantly increased (p < 0.0001) when tissue was treated with immune sera (66.0+/-10.0 microg/mg versus 22.6+/-4.8 microg/mg in control tissue). Graft specificity of immune sera was confirmed by Western blot analysis. CONCLUSIONS These results strongly suggest a role of circulating graft-specific antibody in the disease of bioprosthetic graft calcification.
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Affiliation(s)
- P Human
- Department of Cardiothoracic Surgery, Cape Heart Center, University of Cape Town Medical School, South Africa.
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Human P, Zilla P. Bioprosthetic Tissue Degeneration Inflammatory and Immune Processes: The Neglected Villain of Bioprosthetic Degeneration? J Long Term Eff Med Implants 2001. [DOI: 10.1615/jlongtermeffmedimplants.v11.i34.80] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Abstract
BACKGROUND Fixation at high glutaraldehyde (GA) concentrations mitigated bioprosthetic calcification in the rat model. The present study intended to verify this observation in the circulatory sheep model. METHODS Porcine aortic roots were either fixed in 0.2%, 1.0%, or 3.0% GA. Eight roots per group were implanted in the distal aortic arch of sheep. After six weeks and six months calcification and inflammation were quantitatively and qualitatively assessed. RESULTS By increasing the GA concentration from 0.2% to 3.0%, aortic wall calcification could be reduced by 38% after 6 weeks and 34% after 6 months of implantation (p < 0.01). Mineralization coincided with the presence of elastin although calcium was predominantly found in cell nuclei and membranes. Leaflet calcification was absent in all groups after 6 weeks but in a few leaflets presented as heterogeneous, nodular spongiosa deposits after 6 months. Overall, differences between 0.2%-, 1.0%-, and 3.0%-fixed tissue were quantitative but not qualitative regarding distribution patterns. There was no significant difference in inflammatory host reaction between all groups. CONCLUSIONS We have shown in the circulatory sheep model that the anticalcific effect of better cross-linking seems to outweigh the intrinsic pro-calcific effect of GA accumulation in bioprosthetic aortic wall tissue.
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Affiliation(s)
- P Zilla
- Department of Cardiothoracic Surgery, University of Cape Town Medical School, South Africa.
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Weissenstein C, Human P, Bezuidenhout D, Zilla P. Glutaraldehyde detoxification in addition to enhanced amine cross-linking dramatically reduces bioprosthetic tissue calcification in the rat model. J Heart Valve Dis 2000; 9:230-40. [PMID: 10772041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
BACKGROUND AND AIM OF THE STUDY Enhanced fixation of bioprosthetic tissue by both increased concentrations of glutaraldehyde (GA) and the introduction of additional cross-links with L-lysine significantly reduces calcification. We have previously reported that prolonged exposure to high-volume amino-compounds under warm, acidic conditions leads to thorough, non-rebounding GA detoxification. The aim of the present study was to prove that removal of excess GA can amplify the benefits of enhanced GA cross-linking with regard to bioprosthetic tissue calcification. METHODS Porcine ascending aortas and leaflet tissue, and bovine pericardium were immediately fixed using three GA concentrations (0.2%, 1.0%, 3.0% (v/v)) for seven days at 4 degrees C. Samples were allocated to nine groups. Groups I to III received no further treatment (one at each GA concentration); groups IV to IX underwent an additional L-lysine interim step (48 h/37 degrees C/0.1 M) two days before completion of standard seven-day GA fixation; and groups VII to IX were additionally treated with a GA extraction process using high-volume urazole solution (acetic acid buffer, pH 4.5, 37 degrees C, one week) followed by NaBH4 reduction (2 days, 37 degrees C). Samples were implanted subcutaneously in rats (six per group) for six weeks. Tissue calcium was measured by atomic absorption spectrophotometry and examined histologically after von Kossa staining. RESULTS Calcification was reduced in all three tissue types by enhanced cross-linking and by extraction of excess GA. Increasing the GA concentration from 0.2% to 3.0% led to a reduction in calcification of 11.5% (p = 0.074; Student's t-test) in leaflets; 63.6% (p <0.0001) in pericardium; and 17.5% (p = 0.034) in aortic wall tissue. The introduction of additional cross-links with L-lysine resulted in a significant reduction of calcium in all tissues (maximally 42.5%, p = 0.0003 in leaflets; 79.3%, p = 0.005 in pericardium; and 49.6%, p <0.0001 in aortic wall; Student's t-test). Optimal reduction in calcification could be achieved with the combined effect of 3.0% GA fixation, L-lysine enhancement and urazole detoxification. When compared with 0.2% GA-fixed tissue, calcification could be reduced by 99.1% in leaflets, 95.9% in pericardium, and 90.8% in aortic wall tissue (p <0.0001 for all tissue types; Student's t-test). CONCLUSION Removal of excess GA from fixed bioprosthetic tissue was capable of markedly improving the anti-calcific effect of enhanced GA cross-linking.
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Affiliation(s)
- C Weissenstein
- Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town Medical School, South Africa
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Zilla P, Weissenstein C, Bracher M, Zhang Y, Koen W, Human P, von Oppell U. High glutaraldehyde concentrations reduce rather than increase the calcification of aortic wall tissue. J Heart Valve Dis 1997; 6:502-9. [PMID: 9330172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND AND AIMS OF THE STUDY This study was performed in order to: (i) determine whether a similar reduction of tissue calcification as seen after prolonged storage can be achieved through higher concentrations of glutaraldehyde (GA); and (ii) verify that well-preserved tissue integrity can suppress calcification. METHODS Before fixation in 0.2% GA (PBS, 4 degrees C, seven days) porcine aortas were kept on ice for 48 h. Alternatively, tissue was immediately fixed at the abattoir in 0.2%, 1.0% or 3% glutaraldehyde (PBS, 4 degrees C, seven days). A second group of immediately fixed tissue (0.2%, 1.0%, 3.0% GA) (PBS, 4 degrees C, two days) had an interim step of L-lysine treatment (0.1M, 37 degrees C, acetic acid buffer, two days) in order to enhance cross-linking followed by warm-temperature fixation (PBS, 37 degrees C, five days). Two animal models were compared: subcutaneous implantation in rats (12 weeks) and vascular implantation in non-human primates, Chacma baboons (six weeks). RESULTS In both animal models the highest level of calcification was found in the group with delayed fixation in 0.2% GA. In the rat model there was an inverse correlation between tissue calcification and the GA concentration used, with 3% GA-fixed tissue showing the lowest level of tissue calcium. Overall, increasing GA concentration had a significant benefit on calcification (p < 0.0001; two-factor analysis of variance). Enhancement of cross-linking with L-lysine further abrogated tissue calcium levels at all GA concentrations (p < 0.0001; two- factor analysis of variance). Although the short-term baboon model showed lower tissue calcium levels, the trend seen in the rat model was confirmed. CONCLUSIONS Our results demonstrate the detrimental effect of delayed fixation and further suggest that, against previous beliefs, fixation at higher glutaraldehyde concentrations reduces the calcification tendency of cross-linked aortic tissue.
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Affiliation(s)
- P Zilla
- Department of Cardiothoracic Surgery, University of Cape Town, South Africa
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Zilla P, Fullard L, Trescony P, Meinhart J, Bezuidenhout D, Gorlitzer M, Human P, von Oppell U. Glutaraldehyde detoxification of aortic wall tissue: a promising perspective for emerging bioprosthetic valve concepts. J Heart Valve Dis 1997; 6:510-20. [PMID: 9330173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND AND AIMS OF THE STUDY Due to its superb crosslinking activity, glutaraldehyde (GA) is still the most widely used fixative for bioprosthetic heart valves. At the same time, however, GA is also believed to be partly responsible for tissue calcification and the lack of surface re-endothelialization, both of which may contribute to valve degeneration. Although excess GA has previously been extracted from thin leaflet tissue, this treatment proved insufficient for the detoxification of thick aortic wall tissue of stentless valves or root prostheses. METHODS In order to establish a detoxification procedure which thoroughly extracts biologically active GA from aortic wall tissue, we used a highly sensitive bioassay where endothelial cells were seeded onto glutaraldehyde-fixed aortic wall discs following various detoxification procedures. Absolute cell numbers and morphologic shape were correlated with shrinkage temperature and shrinkage extent of the tissue to determine the potential of the treatments to reverse crosslinks. To optimize treatment conditions, pH (3.2 versus 4.5), temperature (22 degrees C versus 37 degrees C) and incubation time (48 h versus one week) were varied. In order to identify an optimal detoxification agent, 12 different amino-reagents from four chemical groups were compared: low pKa aromatic amines, amino acids, low pKa N-heterocyclic compounds and amino sugars. RESULTS Amino-reagent treatment required warm temperature (37 degrees C), prolonged reaction time (one week) and a pH of 4.5 to achieve long-term cell growth on glutaraldehyde-fixed aortic wall. All 12 amino-reagents were able to detoxify aortic tissue satisfactorily; and all mildly reversed crosslinks, although there were differences between candidates. When summarized data were ranked correlating cell growth and quality with shrinkage temperature and shrinkage extent, seven reagents had a rank sum above the overall mean value, and five below with statistically significant differences between candidates. The additional stabilization of the detoxification reaction through borohydride-reduction had no further effect on tissue biocompatibility and crosslinks. CONCLUSIONS Efficient detoxification of thick aortic wall tissue is possible if a one-week incubation in an acetic acid buffer-based amino-reagent is carried out at 37 degrees C.
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Affiliation(s)
- P Zilla
- Department of Cardiothoracic Surgery, University of Cape Town, South Africa
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Zilla P, Zhang Y, Human P, Koen W, von Oppell U. Improved ultrastructural preservation of bioprosthetic tissue. J Heart Valve Dis 1997; 6:492-501. [PMID: 9330171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND AND AIMS OF THE STUDY Poor ultrastructural tissue preservation of bioprosthetic heart valves is associated with a higher propensity for calcification. In spite of this realization, commercial valve fixation remains suboptimal. METHODS In an attempt to maintain tissue integrity through improved cross-linking procedures, transmission electron microscopy and a 21-point damage score were applied to assess the ultrastructural preservation of aortic wall tissue-the main component of contemporary aortic valve bioprostheses. An ideal glutaraldehyde (GA) concentration was assessed by immediate tissue fixation at 4 degrees C comparing 0.2%, 0.5%, 0.65%, 1.0%, 2.0%, 3.0% and 4.0% GA in phosphate-buffered saline (PBS). Subsequently, an optimal concentration of 3.0% GA was used to determine the effect of fixation temperature (4 degrees, 22 degrees and 37 degrees C). Finally, the superior glutaraldehyde concentration (3.0%) and cross-linking temperature (4 degrees C) were used to assess tolerance towards delayed fixation. RESULTS When different GA concentrations were used almost identical damage scores of 6.3 and 5.8 were found for 0.2% and 0.65% fixation. The first significant improvement was found at a concentration of 1.0% (score 3.3; p < 0.01) followed by a further improvement at 3.0% (score 2.6; p = 0.05). The optimal fixation temperature was 4 degrees C (3.7) with the worst results obtained at room temperature (score 9.2; p < 0.03). When fixation was delayed, the most significant damage occurred during the initial 30 min after slaughter (from 2.3 to 7.4; p < 0.02) followed by another significant deterioration between 4 and 16 h (from 5.6 to 9.7; p < 0.02). CONCLUSIONS In summary, the prerequisites for an ideal ultrastructural preservation of bioprosthetic aortic wall tissue are immediate fixation (within 30 min), high GA concentrations (> 1.0%) and cold-temperature fixation (4 degrees C).
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Affiliation(s)
- P Zilla
- Department of Cardiothoracic Surgery, University of Cape Town, South Africa
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Hildebrandt A, Meiser B, Human P, Reichenspurner H, Rose A, Odell J, Reichart B. FK 506: short- and long-term treatment after cardiac transplantation in nonhuman primates. Transplant Proc 1991; 23:509-10. [PMID: 1703694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- A Hildebrandt
- Department of Cardio-Thoracic Surgery, University of Munich, West Germany
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McDonogh M, Human P, Odendaal W. Mucorsinusitis in diabetes. S Afr Med J 1985; 67:78. [PMID: 3917580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
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