In Vitro Calcification of Bioprosthetic Heart Valves: Method Validation by Comparative Heart Valve Calcification Testing.

Tissue calcification is a major cause of failure of bioprosthetic heart valves. Aim of this study was to examine whether surface heparin treatment of the decellularized porcine heart valve reduces tissue calcification. Fresh porcine aortic heart valves were dissected as tissue discs and divided into four groups. Group A: controls without treatment, Group B: decellularization only, Group C: decellularization and glutaraldehyde cross-linking, Group D: decellularization and glutaraldehyde cross-linking followed by surface heparin treatment. After implantation in New Zealand White rabbits for 60 days, the explanted heart valve discs from the different study groups underwent a series of histological examinations as well as determination of calcium content by the methyl thyme phenol blue colorimetric method. Results of the explanted heart valve discs for the Von Kossa staining demonstrated that in Group A the heart valve tissue was the most severely stained with black color, whereas in Group D there was hardly any area that was stained black after implantation indicating the least tissue calcification. Furthermore, the inflammatory cells identified by the Hematoxylin-eosin staining appeared to be the least in Group D. The average tissue calcium content was highest in Group A (0.197 ± 0.115 μmolmg-1 ), modest in Group B (0.113 ± 0.041 μmolmg-1 ), and Group C (0.089 ± 0.049 μmolmg-1 ), and the lowest in Group D (0.019 ± 0.019 μmolmg-1 , p < 0.05). These results suggest that surface heparin treatment tends to reduce tissue calcification of the dellellularized porcine heart valve in a rabbit intramuscular implantation model. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 400-405, 2017.

Calcification is a major reason for the failure of bioprosthetic heart valves. Therefore, several attempts towards an accelerated in vitro model were undertaken in order to provide a cost- and time-saving method for the analysis of calcification processes. Due to the problem of superficial or spontaneous precipitation, which occurred in the fluids applied, we focused our study on the development of a near-physiological calcification fluid. The desired fluid should not precipitate spontaneously and should neither promote nor inhibit calcification. Eleven different fluid compositions were tested without contact to potentially calcifying materials. Crucial factors regarding the fluid properties were the ionic product, the ionic strength, and the degree of supersaturation concerning dicalciumphosphate-dihydrate, octacalciumphosphate, and hydroxyapatite. The fluids were kept in polyethylene bottles and exposed to a slight vibration within a durability tester at 37°C. The precipitation propensity was monitored optically and colorimetrically. A structural analysis of the deposits was carried out by x-ray powder diffraction and IR-spectroscopy, which showed the development of the crystal phases that are relevant in vivo. Only two of the fluids did not precipitate. Resulting from the computations of the effective fluid contents, the saturation degree concerning dicalciumphosphate-dihydrate seems to be the key factor for spontaneous precipitation.

Reoperation for structural failure of bioprosthetic heart valves carries considerable surgical risk. In this report, investigators describe the results of transcatheter heart valve implantation in 24 patients with degenerating bioprostheses. The failing valves were aortic in 10 patients, mitral in 7, pulmonary in 6, and tricuspid in …

Bioprosthetic heart valves have been used since the 1960s, starting with the use of homograft aortic valves obtained from human cadavers. Today prosthetic heart valves are used widely, and bioprostheses account for close to 40% of all heart-valve replacements. Although most bioprosthesis are still stented porcine aortic valves, the introduction of stentless valves and the increasing use of cryopreserved homograft valves has led to an upsurge of interest in bioprosthesis. There have been significant changes in the handling and fixation of porcine aortic valves; however, their modes of failure remain virtually unchanged, although many bioprosthetic valves now last for considerably longer periods. This article reviews the modes of failure of bioprosthetic heart valves.

Relevance of immunologic reactions for tissue failure of bioprosthetic heart valves

In this issue of Circulation , Dr Manji and colleagues1 from the University of Alberta (Canada) report a series of animal experiments designed to test the mythic role of gluteraldehyde in preventing recognition of bioprosthetic heart valve antigenicity with subsequent rejection and failure. Gluteraldehyde–cross-linked xenograft tissues (initially porcine) have been used in the manufacturing of stented (and now stentless) heart valves since 1970. Original theories for the clinical efficacy of gluteraldehyde were based on its ability to irreversibly cross-link collagen and thus to increase mechanical strength and durability over fresh untanned cardiovascular tissues. Porcine valve leaflets, bovine pericardium, equine pericardium, and bovine jugular vein, among other structures, have been treated this way for clinical applications. Since its introduction, however, limitations and unexpected consequences of gluteraldehyde and similar chemical treatments have been recognized clinically. As pointed out by the authors, durability is quite variable, tending to be better in older patients whereas younger patients suffer early deterioration, calcification, and fibrocalcific failure.2,3 The good news has been that the failures tend to be progressive rather than catastrophic, leading to semielective reoperations. Additionally, the xenograft bioprostheses have been extremely helpful in avoiding warfarin in the very young and the very old, reducing the risk of thromboembolism. The traditional explanation for the fibrocalcific degeneration of the nonvital gluteraldehyde-treated bioprosthetic heart valves has been a combination of physical and chemical effects leading to calcification and a fixation of the structural proteins that prevent protein recycling and renewal. Mechanical theories of fatigue-induced wear resulting in calcification have been proposed, especially along the flexion lines of the cusps. Others have proposed that the gluteraldehyde has serendipitously “masked” the antigenicity of xenograft proteins, retained cells, and cellular debris, thus prolonging the period to calcification. This well-designed series of studies buttresses other studies demonstrating that gluteraldehyde fixation …

Prevention of Calcification of Bioprosthetic heart Valve Leaflets by Ca2+ Diphosphonate Pretreatment

Calcification is the principal cause of the clinical failure of bioprosthetic heart valves (BHV). Calcification occurs through an interaction of host and implant factors, mainly younger age and glutaraldehyde pretreatment, respectively. The hypothesis of this work was that an impaired balance between positively and negatively charged amino acids, due to the reaction with Lys and Hyl tissue-collagen residues, expose affinity sites to Ca++. We further hypothesized that regardless of the cause(s) of BHV calcification, positive charge modification of the tissues will prevent their propensity to calcify. Modification of BHV tissue was obtained by covalently binding protamine sulfate, a polybasic peptide, via formaldehyde and subsequent glutaraldehyde tissue crosslinking. Protamine-bound tissue exhibited stability properties (shrinkage temperature and resistance to collagenase digestion) similar to BHV tissue. Protamine-treated tissue was less permeable to Ca++, and reduced staining was observed with positively charged dyes, indicating the presence of positively charged functional groups in the modified tissue. Significant prevention of calcification was exhibited by the p-bound tissue in comparison to BHV tissue, 30.9 and 109 micrograms/mg calcium, respectively, after 30 days of subdermal implants in rats. The modification procedure resulted in stable, covalent links of approximately 10% w/w protamine with undiminished anticalcification properties, even after 1 year storage. The results support our hypotheses, and orthotopical heart valve replacements are required in order to completely evaluate the treatment efficacy and biocompatibility.

Calcification is the principal cause of the clinical failure of bioprosthetic heart valves (BHV). The hypothesis of this work was that an impaired balance between positively and negatively charged amino acids, due to the reaction with Lys and Hyl tissue-collagen residues, expose affinity sites to Ca++. We further hypothesized that regardless of the cause(s) of BHV calcification, positive charge modification of the tissue will prevent their propensity to calcify. Modification of BHV tissue was obtained by covalently binding protamine sulfate, a polybasic peptide, via glutaraldehyde. The modification procedure resulted in stable, covalent links of approximately 5.3% w/w protamine with undiminished anticalcification properties, even after long storage. Significant prevention of calcification was exhibited by the p-bound tissue in comparison to BHV tissue, 66.0 and 106.5 micrograms/mg calcium, respectively, after 30 days of subdermal implants in rats. The results support our hypotheses, and orthotopical heart valve replacements are required in order to completely evaluate the treatment efficacy and biocompatibility.

Generally, the dysfunction or failure of bioprosthetic heart valves (BHVs) is managed by replacement surgery. In the case of tricuspid valve dysfunction, re-do surgery is rarely attempted because of the critically high risk of developing pulmonary hypertension, pulmonary embolism, and intraoperative mortality. Hence, transcatheter tricuspid repair and replacement procedures are preferred. More recently, transcatheter valve-in-valve (ViV) treatments have gained importance because of their less invasiveness, especially for patients with prior surgeries. Encouraging evidence of the safety and effectiveness of a novel balloon-expandable (BE) transcatheter heart valve (THV)—the Myval THV—has been reported for ViV procedures. Here, we present a case-series of 5 patients, in whom tricuspid ViV procedure was performed using BE Myval THV, implanted supra-annularly by anchoring onto the deteriorated BHV. This case-series details the procedural steps to prevent in-hospital adverse events and early (30-day) mortality and the challenges during tricuspid ViV interventions.

Cardiovascular implant mineralization involving bioprosthetic materials, such as glutaraldehyde cross linked porcine aortic valves or synthetic materials such as polyurethanes, is an important problem that frequently leads to clinical failure of bioprosthetic heart valves, and complicates long-term experimental artificial heart device implants. Novel, proprietary, calcification resistant polyetherurethanes (PEU) as an alternative to bioprosthetic materials were the subject of these investigations. A series of PEU was derivatized through a proprietary reaction mechanism to achieve covalent binding of 100 to 500 nM/mg of bisphosphonate (2-hydroxyethane bisphosphonic acid, HEBP). The stability of HEBP (physically dispersed or covalently bound) verified by studying the release kinetics in physiological buffer (pH 7.4) at 37 degrees C, demonstrated the covalent binding reaction to be stable, efficient, and permanent. Surface (FTIR-ATR, ESCA, SEM/EDX) and bulk (solubility, GPC) properties demonstrated that the covalent binding of HEBP occurs in the soft segment of the PEU, reduces surface degradation, and does not affect the original material properties of the PEU (prior to derivatization). In vitro calcium diffusion of the derivatized PEU showed a decrease in calcium permeation as the concentration of HEBP covalent binding was increased. In vivo properties of underivatized and derivatized PEU (containing 100 nM of covalently bound HEBP) were studied with rat subdermal implants for 60 days. Explants demonstrated calcification resistance due to the covalently bound HEBP without any side effects. It is concluded that a PEU containing HEBP might serve as a calcification resistant candidate material for the fabrication of a heart valve prosthesis and other implantable devices.

It has been hypothesized that repetitive flexural stresses contribute to the fatigue-induced failure of bioprosthetic heart valves. Although experimental apparatuses capable of measuring the bending properties of biomaterials have been described, a theoretical framework to analyze the resulting data is lacking. Given the large displacements present in these bending experiments and the nonlinear constitutive behavior of most biomaterials, such a formulation must be based on finite elasticity theory. We present such a theory in this work, which is capable of fitting bending moment versus radius of curvature experimental data to an arbitrary strain energy function. A simple finite element model was constructed to study the validity of the proposed method. To demonstrate the application of the proposed approach, bend testing data from the literature for gluteraldehyde-fixed bovine pericardium were fit to a nonlinear strain energy function, which showed good agreement to the data. This method may be used to integrate bending behavior in constitutive models for soft tissue.

Reoperation for bioprosthetic heart valve failure is associated with significant morbidity and mortality, particularly in high-risk patients. Transcatheter valve-in-valve (VIV) implantation may offer a less invasive alternative. The aim of this study was to report our initial experience with transcatheter VIV implantation to treat degenerated tissue valves. VIV implantation with the Edwards SAPIEN transcatheter heart valve (THV; Edwards Lifesciences Inc, Irvine, CA, USA) was performed in 18 high-risk patients (STS 8.2±5.2%; logistic EuroSCORE 37.4±20.8%) with symptomatic bioprosthetic failure (17 aortic, one mitral). Valve Academic Research Consortium (VARC) definitions were applied for endpoint adjudication. Transfemoral access was the preferred vascular approach (16 patients, with the mitral VIV delivered anterogradely through the femoral vein; one transaxillary and one transapical). The majority (83%) of procedures were performed under local anaesthesia and sedation. Device success was achieved in all but one patient who had a final transaortic gradient ≥20mmHg. Acute kidney injury occurred in three patients (Stage 3 in 1), life-threatening or major bleeding in four patients, while major vascular complications occurred in one patient. Permanent pacemaker implantation was required in two patients. There were no deaths or neurological events at 30-day follow-up. At a median follow-up of 11 months (interquartile range 6-16), the mortality rate was 5.6% and all patients were in NYHA class II or lower. Transcatheter implantation of the Edwards THV within a degenerated aortic bioprosthesis, performed predominantly via the transfemoral route, is feasible and associated with good periprocedural and clinical outcomes in high-risk surgical patients.

Controlled-Release Drug Delivery of Diphosphonates to Inhibit Bioprosthetic Heart Valve Calcification: Release Rate Modulation with Silicone Matrices Via Drug Solubility and Membrane Coating

Triglycidyl Amine Crosslinking Combined With Ethanol Inhibits Bioprosthetic Heart Valve Calcification