Time-dependent effect of glutaraldehyde on the tendency to calcify of both autografts and xenografts

Partial Tracheal Defects Closure using Glutaraldehyde-Treated Autologous Pericardium

BACKGROUND

The usefulness of autologous pericardium treated with glutaraldehyde (GA) for tracheal defect closure is unknown. This study preliminarily evaluated whether a GA-treated autologous pericardial graft can effectively close tracheal defects in a beagle model.

METHODS

Defects of 10 mm × 10 mm were created on the trachea of 10 beagles and divided into a GA-treated group (n = 5), with tracheal reconstruction using GA-treated pericardium, and control group (n = 5), using fresh pericardium. Repair sites were evaluated through bronchoscopy and histology. Blood flows on graft were measured using laser Doppler technique on postoperative days (PODs) 0, 4, 7, 14, 28, and 56. Repair sites were histologically evaluated on POD 56. In addition, GA-treated pericardia of three other beagles were histologically evaluated 12 months postoperatively, for long-term follow-up.

RESULTS

All animals survived; none developed anastomotic insufficiency. The mean suturing time and frequency of additional suture were significantly shorter and lower in the GA-treated group than in the control group (p = 0.002, 0.004). All animals in the control group exhibited graft contraction, whereas the GA-treated group healed with most graft residual and reepithelialization in the bronchoscopic and histological findings (p = 0.01, 0.004). Further, all long-term GA-treated pericardia of three beagles were confirmed as residual grafts with reepithelialization, without contraction, at 12 months postoperatively. Blood flows on graft using laser Doppler technique in the GA-treated group were detected at POD 14 or thereafter.

CONCLUSION

GA-treated pericardium was easier to handle and provided favorable scaffolding, without graft contraction, compared with the nontreated pericardium at short- and long-term follow-up.

Long-term outcome of extensive mitral valve reconstruction with autologous pericardium and artificial chordae for treatment of destructive active infective endocarditis of the mitral valve

Objective

Mitral valve (MV) repair is a well-accepted surgical approach for infective endocarditis (IE). In our hospital, extensive MV reconstruction with fresh autologous pericardium (AP) and artificial chordae (AC) has been performed for patients with profoundly extensive and destructive IE in which valve reconstruction would be extremely challenging, especially in young patients to avoid mechanical valve replacement. Long-term outcome including the future performance of the newly created leaflet has not been established.

Methods

Five patients (54 (38–60) years of age; 3 men, 2 women) underwent this procedure from January 2011 to April 2022. In all patients, preoperative cardiac function was good (left ventricular ejection fraction, 69 (66–75)). After complete debridement of the infective valve tissue, the MV was reconstructed with large, fresh, trimmed AP and AC.

Results

The reconstructed leaflets were anterior in three patients and posterior in four, and AC were placed in four patients. All patients showed an uneventful postoperative course and were discharged to home 36 (28–42) days postoperatively after completion of intravenous antibiotic therapy. Pre-discharge echocardiography revealed no or trivial mitral regurgitation (MR) in all patients. The median follow-up period was 9.6 (6.0–10.4) years, and no patients developed recurrence of the IE. The latest echocardiography in four patients showed trivial/mild MR with good leaflet function. One patient developed recurrence of MR, 5 months postoperatively.

Conclusions

The short- and long-term outcomes of this procedure might be acceptable. This procedure might be considered as an effective and valuable option, especially in young patients.

Biofabrication in Congenital Cardiac Surgery: A Plea from the Operating Theatre, Promise from Science

Despite significant advances in numerous fields of biofabrication, clinical application of biomaterials combined with bioactive molecules and/or cells largely remains a promise in an individualized patient settings. Three-dimensional (3D) printing and bioprinting evolved as promising techniques used for tissue-engineering, so that several kinds of tissue can now be printed in layers or as defined structures for replacement and/or reconstruction in regenerative medicine and surgery. Besides technological, practical, ethical and legal challenges to solve, there is also a gap between the research labs and the patients' bedside. Congenital and pediatric cardiac surgery mostly deal with reconstructive patient-scenarios when defects are closed, various segments of the heart are connected, valves are implanted. Currently available biomaterials lack the potential of growth and conduits, valves derange over time surrendering patients to reoperations. Availability of viable, growing biomaterials could cancel reoperations that could entail significant public health benefit and improved quality-of-life. Congenital cardiac surgery is uniquely suited for closing the gap in translational research, rapid application of new techniques, and collaboration between interdisciplinary teams. This article provides a succinct review of the state-of-the art clinical practice and biofabrication strategies used in congenital and pediatric cardiac surgery, and highlights the need and avenues for translational research and collaboration.

Midterm Results of Mitral Valve Repair With Pericardial Leaflet Augmentation: A Single-Center Experience

In certain pathologies, mitral valve repair is complicated by a paucity of tissue caused by fibrosis or destruction. Utilization of autologous pericardium for leaflet augmentation may be the only option to repair these valves. We present the midterm results of mitral valve leaflet augmentation with glutaraldehyde-fixed autologous pericardium. One hundred thirty consecutive patients undergoing mitral valve repair with glutaraldehyde-fixed pericardial augmentation of leaflets were followed up clinically and by echocardiography at 6-month intervals. Mean age was 24.8 years (range 2-64). The etiology was rheumatic in 75.3%, indeterminate in 8.4%, and other in 16.1%. Out of the rheumatics, 57.1%, 24.4%, and 18.3% had combined mitral stenosis and mitral regurgitation, isolated mitral regurgitation, and mitral stenosis, respectively. About 21.5% had a recent history of rheumatic activity. Eight were operated emergently for intractable heart failure. Majority of the patients required repair of multiple components of the mitral valve apparatus. Leaflet peeling was done in 52.3%. Pericardial patch augmentation of anterior mitral leaflet, posterior mitral leaflet, or both were carried out in 61.5%, 34.6%, and 3.8% patients respectively. Sixty percent got chordal procedures, while 92.3% got annuloplasty. There were no deaths during the mean follow-up period of 28 months. Ninety-three percent of our patients were in New York Heart Association class I and II on follow-up. There were 11 repair failures. Seven patients underwent a reoperation, while 4 patients are being managed conservatively (reoperation rate 5.38%). Augmentation of mitral valve leaflets with autologous pericardium allows many significantly fibrosed and destroyed valves to be reliably repaired with good midterm durability and hemodynamics.

Small Diameter Xenogeneic Extracellular Matrix Scaffolds for Vascular Applications

Currently, despite the success of percutaneous coronary intervention (PCI), coronary artery bypass graft (CABG) remains among the most commonly performed cardiac surgical procedures in the United States. Unfortunately, the use of autologous grafts in CABG presents a major clinical challenge as complications due to autologous vessel harvest and limited vessel availability pose a significant setback in the success rate of CABG surgeries. Acellular extracellular matrix (ECM) scaffolds derived from xenogeneic vascular tissues have the potential to overcome these challenges, as they offer unlimited availability and sufficient length to serve as "off-the-shelf" CABGs. Unfortunately, regardless of numerous efforts to produce a fully functional small diameter xenogeneic ECM scaffold, the combination of factors required to overcome all failure mechanisms in a single graft remains elusive. This article covers the major failure mechanisms of current xenogeneic small diameter vessel ECM scaffolds, and reviews the recent advances in the field to overcome these failure mechanisms and ultimately develop a small diameter ECM xenogeneic scaffold for CABG. Impact Statement Currently, the use of autologous vessel in coronary artery bypass graft (CABG) is common practice. However, the use of autologous tissue poses significant complications due to tissue harvest and limited availability. Developing an alternative vessel for use in CABG can potentially increase the success rate of CABG surgery by eliminating complications related to the use of autologous vessel. However, this development has been hindered by an array of failure mechanisms that currently have not been overcome. This article describes the currently identified failure mechanisms of small diameter vascular xenogeneic extracellular matrix scaffolds and reviews current research targeted to overcoming these failure mechanisms toward ensuring long-term graft patency.

Bioengineered tissue solutions for repair, correction and reconstruction in cardiovascular surgery

The treatment of cardiac alterations is still nowadays a dramatic issue in the cardiosurgical practice. Synthetic materials applied in this surgery have failed in their long-term therapeutic efficacy due to low biocompatibility and compliance, especially when used in contractile sites. In order to overcome these treatment pitfalls, novel solutions have been developed based on biological tissues. Patches in pericardium, small intestinal submucosa, as well as engineered tissues of myocardium, heart valves and blood vessels have undergone a large preclinical investigation in regenerative medicine studies. Clinical translation has been started or reached by several of these new bioengineered treatment alternatives. This review will describe the preclinical and clinical experiences realized so far with the application of biological tissues in cardiovascular surgery. It will depict the progressive steps realized in the evolution of this research, as well as it will point out the challenges yet to face in order to generate the ideal biomaterial for cardiovascular repair, corrective and reconstructive surgery.

Current surgical strategies and techniques of aortic valve diseases in children

While the long-term outcome of surgical aortic valvotomy (SAV) appears to be better than that of balloon aortic valvuloplasty (BAV) as the primary procedure of aortic valve stenosis, the surgical strategies and techniques of treating aortic valve disease in children in other situations remain controversial. Valve repair should be first considered while replacement is still unavoidable in some cases, and new repair techniques developed by innovative surgeons are gradually becoming adopted. Some complex repair procedures such as cusp extension, leaflet replacement/reconstruction have provided satisfactory outcomes. The Ozaki technique replaces aortic valve leaflets with glutaraldehyde-treated autologous pericardium instead of replacing the valve entirely. Special instruments have been developed to make the Ozaki technique more reproducible and standardized. Neonates and infants undergoing aortic valve replacement (AVR) are a high-risk group, where repair should be the primary consideration rather than replacement. Several systematic reviews reveal that all currently available aortic valve substitutes such as pulmonary autograft, mechanical prosthesis, homograft and bioprosthesis are associated with suboptimal results in children, but pulmonary autograft appeared to be superior with high freedom from reintervention and better hemodynamic performance. The strategy for treatment of aortic valve disease should be specifically analyzed based on the brief of being beneficial for children.

Tissue processing techniques for fabrication of covered stents for small-diameter vascular intervention

Animal-derived pericardial tissue is a widely used biomaterial typically treated with glutaraldehyde (GA) to achieve immunological acceptance and long-term durability. However, GA fixation of biological tissue is associated with long-term failure due to degeneration and calcification. In this study, we evaluated two alternative tissue processing methods for the fabrication of pericardial tissue covered stents: detergent-based decellularization (decell) and limited exposure to GA (gentle-glut). Processed pericardial tissues were extensively characterized both in-vitro and in-vivo. Small-diameter covered stents were fabricated and the ability to seal perforation was evaluated in a flow circuit under physiological blood flow conditions. Results indicate that decell-treated tissue appeared with preserved architecture, tissue strength and stability. Gentle-glut tissue appeared with preserved architecture and increased tissue stability, compared to fresh, unprocessed tissue. Reduction of bioburden was demonstrated for both types of alternative treatments, as for GA fixation. Tensile testing demonstrated that both decell- and gentle-glut treated tissues respond better to low strain, as may occur during balloon inflation and stent deployment. Upon subcutaneous implantation in mice, gentle-glut and to a greater degree decell-treated tissue, elicit better host response, with evidence of active tissue remodeling and no detectable calcification, as compared with GA-treated tissue. Small-diameter stents covered with tissues from all groups successfully sealed perforation under physiological blood flow conditions in-vitro, without compromising flow. In summary, covered stents may perform better with pericardial tissue processed according to the methods described in this study. Adopting this methodology to other types of cardiovascular implants and tissues is also suggested.

STATEMENT OF SIGNIFICANCE

Pericardial tissue is a widely used biomaterial for cardiovascular implants, such as covered stents. The use of glutaraldehyde (GA) has become the method of choice for pericardial tissue fixation, making it immunologically acceptable in humans. However, GA-treated tissue is prone to several problems, such as degeneration and calcification that may lead to long-term failure. Here, we studied two alternative tissue processing techniques: fixative-free decellularization and limited exposure to GA. We've shown that both methods achieve better mechanical properties and promote better host acceptance, tissue remodeling and long-term durability. Since the availability of autologous tissue for transplantation is limited, these methods should be adopted for other types of cardiovascular devices, such as bioprosthetic valves, ultimately achieving better long-term results for patients.

Effects of glutaraldehyde concentration and fixation time on material characteristics and calcification of bovine pericardium: implications for the optimal method of fixation of autologous pericardium used for cardiovascular surgery

Objectives

Autologous pericardium, which is widely used in the field of cardiovascular surgery, is usually fixed with glutaraldehyde (GA) to improve handling and provide biomechanical stability. However, an optimal method of GA fixation of autologous pericardium is not known. The objective of this study was to evaluate the effects of GA concentration and fixation time on material characteristics and calcification of bovine pericardium.

Methods

Bovine pericardial tissues were fixed with different concentrations of GA (0.3, 0.4, 0.5 and 0.6%) for different exposure times (10 and 20 min). Material characteristics of the fixed tissues were assessed by mechanical test, thermal stability test and pronase test. The tissues were subcutaneously implanted into 3-week-old rats for 2 months, and the calcium contents of the explanted tissues were measured. Differences between the groups were evaluated by two-way analysis of variance.

Results

Differently treated tissues showed no significant differences in tensile strength. The mean elongation at break of the pericardial tissues fixed with 0.5 and 0.6% was significantly higher compared with 0.3 and 0.4% when fixed for 20 min. The mean elongation at break of the pericardial tissues fixed for 20 min was significantly higher compared with 10 min when fixed with 0.5 and 0.6%. Thermal stability test revealed significantly higher mean shrinkage temperature of the pericardial tissues fixed with 0.6% compared with lower concentrations irrespective of fixation time. The mean shrinkage temperature of the pericardial tissues fixed for 20 min was significantly higher compared with 10 min irrespective of GA concentration. Pronase test revealed significantly lower mean percent remaining weight of the pericardial tissues fixed with 0.3% compared with higher concentrations irrespective of fixation time. The mean percent remaining weight of the pericardial tissues fixed for 20 min was significantly higher compared with 10 min irrespective of GA concentration. The mean calcium content of the pericardial tissues fixed with 0.6% was significantly lower than that of the pericardial tissues fixed with 0.4% irrespective of fixation time.

Conclusions

Fixation of bovine pericardium with 0.5 and 0.6% GA for 20 min produced superior results with regard to material characteristics (mechanical properties, degree of fixation and resistance to enzymatic degradation) and postimplantation calcification. These results may have implications for optimal fixation of autologous pericardium used for cardiovascular surgery.

Mitral Valve Stenosis Progression Due to Severe Calcification on Glutaraldehyde-Treated Autologous Pericardium: Word of Caution for an Attractive Repair Technique

A 42-year-old woman presented with a 6-month history of palpitations and progressive dyspnea on exertion. She had undergone aortic and mitral valve repair using glutaraldehyde-treated autologous pericardium for active infective endocarditis 5 years prior. Transthoracic echocardiography showed mitral valve stenosis with limited movement of the anterior leaflet. At redo surgery, severe calcification of the glutaraldehyde-treated pericardial patch on the anterior mitral leaflet was observed. Double valve replacement was performed with pulmonary vein isolation. Pathologic examination showed calcification of the glutaraldehyde-treated autologous pericardium. The patient was discharged on postoperative day 11 with oral anticoagulant therapy.

Biostability, durability and calcification of cryopreserved human pericardium after rapid glutaraldehyde-stabilization versus multistep ADAPT(R) treatment in a subcutaneous rat model

OBJECTIVES

Autologous pericardium rapidly fixed with glutaraldehyde (GA) in theatre is considered in many cardiac surgery centres the best material currently available for intracardiac, valvular or vascular repair. Implanted non-fixed autologous tissues suffer rapid degeneration, shrinkage and absorption whereas standard xenotypic fixed tissues cause local cytotoxicity and calcification. In the present study, using a subcutaneous rat model, we tested the biostability, durability and calcification potential of four different pericardium patches treated with GA and relevant to current clinical practice.

METHODS

Pericardium samples were divided into four groups according to the method of treatment. Group I consisted of bovine pericardium (BP) fixed with 0.6% GA (control), Group II cryopreserved human pericardium (CHP) rapidly fixed with 0.6% GA for 4 min and detoxified with MgCl2, Group III CHP treated with the multistep ADAPT(®) process (delipidized, decellularized with Tx-100, deoxycholate, IgePal CA-630 and denucleased, fixed in 0.05% monomeric GA and detoxified) and Group IV BP treated with the multistep ADAPT(®) process (CardioCel(®)). Biostability was determined by shrinkage temperature which measures the degree of cross-linking, and durability assessed by resistance to a mixture of proteinases (pronase digestion). Treated pericardium samples (n = 10 in each of Groups I-IV) were implanted in the subcutaneous rat model for 8 and 16 weeks, followed by histology and calcium analysis (atomic absorption spectrophotometry).

RESULTS

The biostability and the durability of both CHP and BP after the multistep ADAPT(®) treatment remained stable without any microscopic calcification. Extractable calcium levels of CHP were significantly (P < 0.01) reduced in Group II (1.89 ± 0.77 μg Ca/mg tissue) compared with Group I (64.37 ± 6.25 μg/mg) after 8 weeks. Calcification of CHP (Group III) and BP (Group IV) after the multistep ADAPT(®) treatment was significantly reduced (1.43 ± 0.48 µg/mg and 0.75 ± 0.10 μg/mg, respectively) compared with Group I (282.52 ± 18.26 μg/mg) and the rapidly treated CHP in Group II (11.32 ± 3.21 μg/mg) after 16 weeks.

CONCLUSIONS

Improved biostability and durability with reduced calcification of tissues after the multistep ADAPT(®) tissue treatment suggest improved alternative substitutes to autologous pericardium.

Is the degeneration of aortic valve bioprostheses similar to that of native aortic valves? Insights into valvular pathology

Aortic stenosis (AS) is the most common valvular disease requiring valve replacement with a prevalence of 2-4% in adults greater than or equal to 65 years of age. There is increasing evidence that AS is an active inflammatory process that is highly regulated, displaying multiple hallmarks of atherosclerosis. Clinically, the definite therapy of advanced AS is prosthetic valve replacement. Herein, bioprosthetic tissue valves (BPs) possess superior thromboresistant and hemodynamic properties compared with mechanical valves. However, cusp degeneration and calcification also limit their long-term outcome. The pathogenesis of BP calcification as well as that of native valves is still poorly understood. Recent studies suggest a similar valvular pathology, that underlies both types of valvular degeneration, but also an even more important role of inflammatory and repair processes in the case of BP degeneration.

Aortic Cusp Extension for Surgical Correction of Rheumatic Aortic Valve Insufficiency in Children

Surgical management of aortic insufficiency in the young is problematic because of the lack of an ideal valve substitute. Potential advantages of aortic valve repair include low incidences of thromboembolism and endocarditis, avoiding conduit replacements, the maintenance of growth potential, and improved quality of life. Aortic valve repair is still far from fulfilling the three key factors that have allowed the phenomenal development of mitral valve repair (standardization, reproducibility, and stable long-term results); however, techniques of aortic valve repair have been refined, and subsets of patients amenable to repair have been identified. We have focused on the oldest technique of aortic valve repair, cusp extension, focusing on children with rheumatic aortic insufficiency. Among 77 children operated from 2003 to 2007, there was one early death from ventricular failure and one late death from sudden cardiac arrhythmia. During a mean follow-up of 12.8 ± 5.9 years, there were 16 (20.5%) reoperations on the aortic valve, at a median of 3.4 years (range, 2 months to 18.3 years) from repair. Freedom from aortic valve reoperation was 96.2% ± 2.2% at 1 year, 94.9% ± 2.5% at 2 years, 88.5% ± 3.6% at 5 years, 81.7% ± 4.4% at 10 years, 79.7% ± 4.8% at 15 years, and 76.2% ± 5.7% at 20 years. Although aortic cusp extension is technically more demanding, it remains particularly more suitable in the context of evolving rheumatic aortic insufficiency in children with a small aortic annulus as a bridge surgical approach to late aortic valve replacement with a larger valvular prosthesis.

Time-dependent change in fresh autologous pericardium applied for posterior mitral annuloplasty: degree of calcification and its influence on the repaired mitral valve

OBJECTIVE

To investigate the degree of calcification of fresh autologous pericardium applied for posterior mitral annuloplasty and its influence on the repaired mitral valve.

METHODS

Thirty-nine patients (31 degenerative and 8 infective endocarditis; mean age at surgery: 62 ± 11 years) were enrolled in this study. Sixteen-slice multi-detector computed tomography was performed to identify calcification of autologous pericardium. The mean clinical follow-up was 4.6 ± 2.6 years (maximum 8.8 years) and the mean computed tomography follow-up period was 3.6 ± 2.5 years (maximum 7.6 years) after surgery.

RESULTS

Pericardial calcification was detected in 15 patients. The earliest detection of calcification was 2.5 years after surgery. There was a weak correlation between pericardial calcification and postoperative years (Pearson's product correlation coefficient: 0.476; p = 0.0019). However, severe calcification of autologous pericardium did not occur in any case. There was no association between pericardial calcification and recurrent mitral regurgitation (p = 0.1145). The mean mitral valve orifice area and the mean transmitral pressure gradient in the 15 patients with calcification were 3.0 ± 0.6 cm(2) and 2.1 ± 1.0 mmHg, respectively.

CONCLUSIONS

Calcification of the fresh autologous pericardium increased with postoperative years. It had no adverse effects on repaired mitral valve in the short-term follow-up period. We will report the findings once again when the follow-up reaches 10 years.

[Heart valve and myocardial tissue engineering]

Cardiac function, including the heart muscle and valves, can be severely altered by congenital and acquired heart diseases. Several graft materials are currently used to replace diseased cardiac tissue and valvular segments. Implantable grafts are either non-vital or can trigger an immune response which leads to graft calcification and degeneration. None of the existing grafts have the ability to remodel and grow in tandem with the physiological growth of a child and therefore require re-operation. Novel approaches such as tissue engineering have emerged as possible alternatives for cardiac reconstruction. The main concept of tissue engineering includes the use of biological and artificial scaffolds that form the shape of the organ structures for subsequent tissue replacement, which will provide absolute biocompatibility, no thrombogenicity, no teratogenicity, long-term durability and growth.Heart valve tissue engineering represents an important field especially in pediatric patients with valve pathologies. In order to create an autologous valve equivalent myofibroblasts and/or endothelial cells are seeded on specially designed scaffolds. Here we describe the different types of cell sources and different types of matrices currently used in heart valve tissue engineering. Valve manufacture is carried out in specially designed bioreactors providing physiological conditions. The number of clinical studies using tissue engineered valves is still limited; however, several promising results have already demonstrated their durability and ability to grow.Myocardial tissue engineering aims to repair, replace and regenerate damaged cardiac tissue using tissue constructs created ex vivo. Conceivable indications for clinical application of tissue engineered myocardial-implant substitutes include ischemic cardiomyopathies, as well as right ventricular outflow tract reconstruction in patients with congenital heart diseases. Therapeutic application of functional (contractile) tissue engineered heart muscle appears feasible once key issues such as identification of the suitable human cell source, large scale expansion and suitable scaffolds are solved. In addition, the present article discusses the importance of vascularization as an important prerequisite for successful bio-artificial myocardial tissue.Further experimental and clinical research on cardiovascular tissue engineering is felt to be of great importance for others as well as for us in order to create an ideal heart valve/myocardial substitute and help our patients with advanced cardiac pathologies.

Fixation of vascular grafts with increased glutaraldehyde concentration enhances mechanical properties without increasing calcification

Our objective was to study the effect of glutaraldehyde (GLU) concentration, heat, and photooxidation on mechanical properties and calcification of bovine pericardium grafts in an in vivo model. Fresh pericardia were treated as follows: 0.625% GLU for 7 days (standard); 0.625%, 1%, and 3% GLU at 4 degrees C for 20 days and 50 degrees C for additional 20 days; irradiation in cross-linking medium with metilene blue at 0 degrees C for 8 hours. Tissues were subjected to tensile mechanical tests (n = 76). Fixed patches were subcutaneously implanted in mice for 50 days (n = 16 per treatment). Calcification was assessed by atomic absorption spectrophotometry (n = 55) and von Kossa staining (n = 28). Analysis of variance and Tukey's test were used for statistical analysis. The 3% GLU and 3% GLU + heat treatments showed an enhancement of the mechanical properties above standard treatment. No significant difference was found in calcification between treatments. The 3% GLU treatment enhances the mechanical properties of the tissue above standard treatment without increasing calcification and without applying heat; therefore it is recommended for high-strength applications. Supplementary treatments to decrease calcification could be combined with this methodology to obtain a high-strength-low-calcification biomaterial for manufacturing of long-term cardiovascular grafts.

Bioprosthetic valve degeneration due to cholesterol deposition in a patient with normal lipid profile

Hypercholesterolemia has been identified as a risk factor for bioprosthetic valvular degeneration, and it has been suggested that statin therapy reduces this risk. The case of a 77-year-old man with low levels of low-density lipoprotein cholesterol (LDL-C) and apolipoprotein B who developed marked LDL-C crystal deposition and a severe foreign body giant cell reaction 21.5 years after aortic bioprosthetic replacement is reported. This observation confirms that cholesterol deposition contributes to bioprosthetic valve degeneration, but that this can occur even in patients with low levels of LDL-C. It suggests that the characteristics of the valve are more critical than the patient's level of LDL-C.

In vivo study of the effects of cryopreservation on heart valve xenotransplantation

BACKGROUND

Recent reports have suggested that cryopreservation reduces the immunogenicity of donor tissue. The immunomodulation by cryopreservation might influence on the tissue durability after xenotransplantation. We investigated the in vivo morphologic changes in cryopreserved xenograft (CXG) heart valves.

MATERIAL AND METHOD

We transplanted a fresh (fresh xenograft; FXG) and a cryopreserved (CXG) porcine aortic root and a cryopreserved canine (cryopreserved allograft; CAG) aortic root into the abdominal aorta of a dog without any immunosuppressive agents. Explanted grafts on the 21st to 49th days after implantation were analyzed morphologically with light microscopy using some special stains, immunohistochemical analysis, and scanning electron microscopy (SEM).

RESULT

Light microscopy showed the absence of smooth muscle cells in the media of the aorta in any group after transplantation. FXG valves did not maintain any cellularity after transplantation. CXG valves contained cellular infiltration in themselves. CAG valves contained numerous fibroblasts, which showed the maintenance of tissue integrity without allowing cellular infiltration. The structure of elastic fibers was well maintained, even in the part of CXG valve with cellular infiltration. Immunohistochemical studies documented the infiltration of T lymphocytes in CXG valves that were labeled by anti-CD3 antibodies. SEM demonstrated that no endothelia were seen on the surface of the valves in any group after transplantation.

CONCLUSION

We concluded that the cryopreservation method might provide an immunomodulation of xenogeneic heart valves for transplantation.

Dynamics of proteins in Golgi membranes: comparisons between mammalian and plant cells highlighted by photobleaching techniques

In less than a decade the green fluorescent protein (GFP) has become one of the most popular tools for cell biologists for the study of dynamic processes in vivo. GFP has revolutionised the scientific approach for the study of vital organelles, such as the Golgi apparatus. As Golgi proteins can be tagged with GFP, in most cases without altering their targeting and function, it is a great substitute to conventional dyes used in the past to highlight this compartment. In this review, we cover the application of GFP and its spectral derivatives in the study of Golgi dynamics in mammalian and plant cells. In particular, we focus on the technique of selective photobleaching known as fluorescence recovery after photobleaching, which has successfully shed light on essential differences in the biology of the Golgi apparatus in mammalian and plant cells.

Porcine stentless bioprostheses: prevention of aortic wall calcification by dye-mediated photo-oxidation

PURPOSE

Aortic wall calcification is problematic in stentless porcine valves. We evaluated the possible anticalcification effect of photo-oxidation on the aortic wall portion of porcine stentless bioprostheses. A comparison with glutaraldehyde-fixed tissue was made.

METHODS

Six Photofix and six Freestyle valves were implanted in juvenile sheep in pulmonary position. Valves were explanted after 3 or 6 months and examined macroscopically, by x-ray, light, and transmission electron microscopy. Calcium content was determined by atomic absorption spectrometry.

RESULTS

The aortic wall portion of all Photofix valves remained free from calcification, while the wall portion of glutaraldehyde-fixed valves calcified strongly, both after 3 and 6 months. Calcium content of the aortic wall portion was: 0.71 +/- 1.27 in the Photofix valves versus 10.78 +/- 77.22 in the Freestyle valves (P < 0.05).

CONCLUSION

Photo-oxidation of a porcine stentless valve prevents calcification not only in the cusps but also in the aortic wall portion.

Bovine pericardium for dural graft: clinical results in 22 patients

BACKGROUND

Bovine pericardium has widely been used for grafts in cardiac surgery and seems to have suitable properties for use as a dural graft. We report our experience of using locally processed bovine pericardium for dural grafts in 22 patients undergoing cranial operations.

METHODS

22 patients were analysed prospectively and followed-up for a maximum 3 years. All available records and information regarding the indication for grafting, graft size, complications and outcome were collected and analysed.

RESULTS

Indications for grafting included neurosurgical, tumour, congenital and trauma patients. Outcomes were classified as good or excellent in 20 patients, whereas in two patients death was not related to surgical closure but more to malignant intracranial hypertension. In no patient was the dural graft a significant factor in the outcome. Bovine pericardium was found to be easily sutured and watertight using standard 4-0 silk suture. This material is relatively inexpensive compared to other non-synthetic grafts.

CONCLUSION

In this clinical assessment, our bovine pericardium better known as Lyolemb was found to be an excellent dural graft material for local and eventual international consumption.

Crosslink formation in porcine valves stabilized by dye-mediated photooxidation

Bovine pericardial and porcine valve materials stabilized by dye-mediated photooxidation have shown potential for bioprosthetic valve use. Previously, in vitro and in vivo stability of these materials was demonstrated through enzymatic, chemical, extraction, rat subcutaneous, and functional challenges. Here, we examine the stability of photooxidized porcine aortic valves through amino acid, crosslink, and hydrothermal isometric tension analysis. Photooxidation reduced intact histidine residues from 17.0 to 0 residues per 1000, indicating the photooxidative alteration of this amino acid. Diphenyl borinic acid-derivitized hydrolyzates of proteins were separated by high-performance liquid chromatography, which identified several amino acid crosslinks that appeared with photooxidation that were absent in untreated controls. Thermal relaxation analysis indicated a significantly higher (p < 0.0002) thermal stability for photooxidized porcine cusps than that of untreated controls, with mean relaxation times for untreated cusps of 14,000 +/- 4650 versus 22,900 +/- 2480 s for photooxidized cusps. In summary, porcine aortic valve tissue treated by dye-mediated photooxidation contains new chemical species and exhibits properties consistent with intermolecular crosslink formation, which explain the increased biostability of this material and its potential for use in bioprosthetic devices.

Valves in development for autogenous tissue valve replacement

Currently available valve and conduit artery substitutes have one or more significant disadvantages including limited durability, thrombogenicity, susceptibility to infection, and a lack of growth potential. Prior attempts to use autologous tissues in the construction of valve or arterial substitutes to overcome some of these limitations have not been successful. The use of tissue engineering techniques to construct valve and arterial substitutes from individual autologous cell lines and biodegradable polymer scaffolds are now under investigation in the laboratory, and the initial short term results in animals have been encouraging. These tissue engineering techniques offer the possibility of creating structures for replacement of valves and conduit arteries which are viable and have the capacity for self-repair and therefore greater durability. In addition, these structures should be non-thrombogenic and less susceptible to infection, and will have growth potential. Copyright 1999 by W.B. Saunders Company

Valvuloplasty with glutaraldehyde-treated autologous pericardium in patients with complex mitral valve pathology

BACKGROUND

Severe mitral regurgitation associated with complex mitral valve disease often precludes successful surgical repair. The feasibility and the results of valvuloplasty with glutaraldehyde-treated autologous pericardium remain largely unknown.

METHODS

The cases of 63 patients who underwent operation within an 11-year period were studied. A pretreated autologous pericardial patch was used for leaflet extension plasty, for paracommissural plasty, as a substitute for part of the leaflet, and for reimplantation of ruptured papillary muscles to eliminate severe mitral regurgitation. Patients with a severely calcified annulus after en bloc decalcification had straddling endoventricular pericardial patch annuloplasty for reconstruction of the affected atrioventricular groove. Chordal replacement with a strip of pericardium was chosen if no suitable chordae were available. Pericardium-reinforced suture annuloplasty was used in patients with acute endocarditis resistant to medical therapy. Associated valvuloplasty procedures with Carpentier techniques were also employed.

RESULTS

There were no operative deaths in this series. At a mean follow-up of 61.1 months (range, 4 to 132 months), mitral regurgitation was absent or trivial in 92.1% of patients by echocardiography. Freedom from reoperation was 95.2% at 1 year and 5 years. Thromboembolic events have not been detected. Thirty percent of patients returned to sinus rhythm. Two patients required valve replacement.

CONCLUSIONS

Our beneficial results indicate that glutaraldehyde-treated autologous pericardium is suitable for valvuloplasty. It provides durable and predictable repair of valves that might otherwise need to be replaced because of the complex mitral valve disease. The technique is reliable, allows further efficacious repair possibilities, and improves postoperative outcomes. Whether it can prevent late deterioration and calcification requires more investigation.

Midterm results after aortic valve replacement with the autologous tissue cardiac valve

OBJECTIVE

To assess midterm results after aortic valve replacement (AVR) with an autologous tissue cardiac valve (ATCV). This new technique was developed to construct a tissue prosthesis for AVR using the patients pericardium, harvested at the time of operation with negligible effect on operating time.

METHODS

Briefly, glutaraldehyde tanned pericardium is mounted on a stent requiring no suturing. Between March 1994 and December 1996, 87 patients, 44/43 M/F and aged 70 +/- 6 years had AVR for aortic stenosis (80%), aortic insufficiency (6%) and combined lesions (14%), one patient suffered from endocarditis. Additional coronary artery bypass was done in 25%, aortic root enlargement in 7%. Aortic cross clamp and cardiopulmonary bypass times were 69 +/- 21 and 93 +/- 29 min. All patients were followed by clinical examination and color flow Doppler echocardiography in 3-12 months interval. Follow up was 99% complete.

RESULTS

There were five perioperative deaths (6%), none of them valve related. Eighty-one patients were followed up to a period of 52 months (mean interval 37.5 +/- 1.3 months), one patient was lost for follow up. Overall survival was 86, 81, 79 and 71% at 12, 24, 36 and 48 months, respectively. There were 14 late deaths with eight (10%) valve related (four cerebral deaths, four sudden deaths). Sixteen patients (20%) had to be re-operated due to severe valve incompetence. Freedom from reoperation was 98, 97, 90 and 63% at 12, 24, 36, and 48 months, respectively. Valve incompetence occurred suddenly, without previous signs in the follow-up examinations. Selection and preparation of the pericardium, the way of fixation of the tissue--brief immersion in glutaraldehyde--and engineering problems might be responsible for this disastrous outcome.

CONCLUSION

Due to these results we must state, that the ATCV did not fulfill our expectations and presently we can not recommend it as an aortic valve substitute.

Polypeptide resurfacing method improves fibroblast's adhesion to hyaluronan strands

Hyaluronic acid (hyaluronan, HyA) is a matrix component that takes part in cell adhesion and growth in normal and repaired tissues. Since it is soluble in water, HyA has been of limited use in tissue engineering of artificial matrices. Recent studies demonstrate that polypeptides have the twin advantages of reducing solubility of HyA and improving cellular attachment via cell surface adhesion molecule receptors. This paper describes a new approach of using a polypeptide resurfacing method to enhance the attachment of cells to HyA strands. HyA strands were crosslinked by glutaraldehyde and then resurfaced with poly-D-lysine, poly-L-lysine, glycine, or glutamine. After inoculation with fibroblasts in vitro, modified HyA was evaluated with histological and immunohistochemical staining methods for cell adhesion and proliferation. Modified HyA with fibroblast cells also were implanted in vivo. The results show that (1) both polylysines enhanced fibroblast adhesion to crosslinked HyA strands; (2) HyA strands were able to be crosslinked well by 3 days of treatment in glutaraldehyde, and as a biomaterial they could resist biodegradation; (3) modified HyA has good biocompatibility, both in vitro and in vivo. The results demonstrate that HyA material resurfaced by polypeptides has positive advantages for cellular adhesion. Resurfaced HyA has much potential as an improved biomaterial for clinical usage.

Aortic valve repair by cusp extension with the use of fresh autologous pericardium in children with rheumatic aortic insufficiency

OBJECTIVES

Our goal was to evaluate the midterm results of aortic valve repair by a more sophisticated tailoring of cusp extension-taking into account the dimensions of the native aortic cusps-with the use of fresh autologous pericardium.

PATIENTS AND METHODS

Forty-one children who had severe rheumatic aortic insufficiency (mean age 11.5 +/- 2.7 years) underwent aortic valve repair by means of this cusp extension technique over a 5-year period. Twenty-four of them underwent concomitant mitral valve repair for associated rheumatic mitral valve disease. All children were then followed up by transthoracic echocardiography before discharge, at 3 and 6 months after the operation, and at yearly intervals thereafter.

RESULTS

Follow-up was complete in all patients and ranged from 3 months to 5 years (median 3 years). No operative and no early postoperative deaths occurred. Only 1 patient died, 9 months after the operation, of septicemia and multiple organ failure. Actuarial survival was 97% at 1 year and has remained unchanged at 3 years. On discharge, the degree of aortic insufficiency was grade 0 for 27 children and grade I for 14. Exacerbation of aortic insufficiency from grade I to grade II was observed in only 1 patient, and none of the children required reoperation for aortic insufficiency during the follow-up period. Mean peak systolic aortic valve gradients at discharge were lower than preoperative values (P =.04), and no significant increase in the peak systolic transvalvular gradient was detected thereafter during the follow-up period. Mean left ventricular dimensions were significantly reduced at discharge when compared with preoperative values (P <.0001).

CONCLUSIONS

Functional results of aortic valve repair with cusp extension using fresh pericardium have been satisfactory at medium term, particularly in children with a small aortic anulus at the time of initial repair, because the expansion potential of fresh autologous pericardium is equivalent to that of the growing sinotubular junction and aortic anulus diameters.

Evaluation of porcine valves prepared by dye-mediated photooxidation

BACKGROUND

Previous studies demonstrated that dye-mediated photooxidation can stabilize bovine pericardium. Here, photooxidized porcine valve cusp and root tissue were assessed in comparison to fresh and glutaraldehyde-treated samples.

METHODS AND RESULTS

In an in vitro tissue solubility test, both photooxidized and glutaraldehyde-treated tissues were resistant to protein extraction compared to fresh tissue. A rat subcutaneous model was used to test in vivo stability and calcification potential. In this study, four of the six fresh leaflets were not visible because of resorption while both photooxidized and glutaraldehyde-treated tissues were biostable. Mineral contents of the rat explants were much lower for both fresh and photooxidized leaflets when compared with glutaraldehyde-treated leaflets. Also, the aortic root calcified whether treated or not with the most mineral being associated with glutaraldehyde-treated root. Analysis of photooxidized porcine valves explanted from the mitral position in sheep indicated a material that was biostable and contained only minor calcification, perhaps due to deformed stents.

CONCLUSIONS

Porcine valve tissue treated by dye-mediated photooxidation is biostable and resistant to calcification, and has potential for use in heart valve bioprostheses.

Assessment of glutaraldehyde crosslinking efficiency with an amine-specific fluorescent probe

BACKGROUND

Crosslinking of heart valves with glutaraldehyde involves the binding of amine groups. We have developed a technique that provides an inverse measure of the degree of tissue fixation by quantifying the amount of unbound amines.

METHODS

Whole aortic valves were exposed to 0.5% glutaraldehyde solution for 0, 1, 15, and 60 minutes, 6 hours, and 1 and 7 days. Frozen sections were exposed to carboxyfluorescein succinimidyl ester, a fluorescent amine-reactive probe. Images were acquired from each section and processed to separate pixels representing tissue from those representing background. An average fluorescent intensity for each image was calculated and related to the number of unbound amines by comparing with standards.

RESULTS

The amount of uncrosslinked amines was observed to decrease exponentially with fixation time and achieved a plateau at 1 day of fixation. A significant difference in the amount of unbound amines also exists between valve leaflets fixed while connected to the root and those excised from the root before fixation.

CONCLUSIONS

This amine measurement technique, being sensitive to spatially varying differences in chemical fixation, should be useful in evaluating the efficacy of new fixation protocols.

Reticulação progressiva de pericárdio bovino com glutaraldeído para confecção de válvulas cardíacas biológicas

Este trabalho descreve um novo processo para a reticulação de matrizes de colágeno com glutaraldeído para a preparação de materiais para a confecção de válvulas cardíacas biológicas, e consiste no tratamento do pericárdio bovino com concentrações progressivamente crescentes com este reagente no intervalo de concentração entre 0,005 e 0,5% em tampão fosfato, pH 7,4. O perfil da reação com glutaraldeído, quando comparado com o procedimento convencional, foi mais homogêneo e os materiais obtidos apresentaram propriedades térmicas e mecânicas similares. Entretanto, mostraram-se significativamente mais estáveis à degradação enzimática, principalmente em relação à tripsina (17 x), que é devido provavelmente à formação de ligações de reticulação mais homogêneas e/ou em maior densidade. Os resultados mostram que metodologia seqüencial estudada, associada ao tratamento convencional, pode constituir-se em uma técnica de pré-tratamento promissora para a preparação de materiais mais eficientes para confecção de biopróteses.