Calcification characteristics of porcine stentless valves in juvenile sheep

Evaluation of Supercritical CO2-Assisted Protocols in a Model of Ovine Aortic Root Decellularization

One of the leading trends in the modern tissue engineering is the development of new effective methods of decellularization aimed at the removal of cellular components from a donor tissue, reducing its immunogenicity and the risk of rejection. Supercritical CO₂ (scCO₂)-assisted processing has been proposed to improve the outcome of decellularization, reduce contamination and time costs. The resulting products can serve as personalized tools for tissue-engineering therapy of various somatic pathologies. However, the decellularization of heterogeneous 3D structures, such as the aortic root, requires optimization of the parameters, including preconditioning medium composition, the type of co-solvent, values of pressure and temperature inside the scCO₂ reactor, etc. In our work, using an ovine aortic root model, we performed a comparative analysis of the effectiveness of decellularization approaches based on various combinations of these parameters. The protocols were based on the combinations of treatments in alkaline, ethanol or detergent solutions with scCO₂-assisted processing at different modes. Histological analysis demonstrated favorable effects of the preconditioning in a detergent solution. Following processing in scCO₂ medium provided a high decellularization degree, reduced cytotoxicity, and increased ultimate tensile strength and Young’s modulus of the aortic valve leaflets, while the integrity of the extracellular matrix was preserved.

A novel restorative pulmonary valved conduit in a chronic sheep model: Mid-term hemodynamic function and histologic assessment

OBJECTIVE

To evaluate the safety and the short-term function of a novel pulmonary valved conduit (Xeltis Pulmonary Valved Conduit; XPV) up to 12 months in a sheep model.

METHODS

XPV and Hancock bioprosthetic valved conduits (H, used as control) were implanted in adult sheep in the pulmonary artery position. Animals were killed at 2 months (n = 6 XPV), 6 months (n = 6 XPV and n = 3 H), and 12 months (n = 6 XPV) and examined histologically. During follow-up, function of the device as well as diameter of both XPV and H were assessed by transthoracic echocardiography.

RESULTS

Of 18 animals that received an XPV, 15 survived until they were killed; 3 animals that received H survived the planned observational interval. XPV showed mild neointimal thickening and degradation beginning at 2 months with an ongoing process until 12 months. Only 1 of the 18 animals with XPV had significant calcification at 6 months. Pathologic specimen did not show any significant narrowing of the conduit whereas neointimal thickness showed a peak at 6 months. Inflammatory process reached a maximum at 6 months and the degradation process at 12 months. Gel permeation chromatography analysis showed molecular weight loss beginning at 2 months with a peak at 12 months for the conduit with slower absorption for the leaflets. The wall of the H conduits showed more neointimal thickening, narrowing, and calcification compared with XPV, but the leaflets demonstrated minimal changes.

CONCLUSIONS

Both conduits demonstrated an acceptable safety and functionality. Significant calcification was rarely observed in the XPV, whereas the H developed more neointimal thickness with calcification of the porcine aortic root portion of the wall.

Evolving Bioprosthetic Tissue Calcification Can Be Quantified Using Serial Multislice CT Scanning

Background. We investigated the value of serial multislice CT scanning for in vivo determination of evolving tissue calcification in three separate experimental settings. Materials and Methods. Bioprosthetic valve tissue was implanted in three different conditions: (1) glutaraldehyde-fixed porcine stentless conduits in pulmonary position (n = 6); (2) glutaraldehyde-fixed stented pericardial valves in mitral position (n = 3); and (3) glutaraldehyde-fixed pericardial tissue as patch in the jugular vein and carotid artery (n = 16). Multislice CT scanning was performed at various time intervals. Results. In stentless conduits, the distribution of wall calcification can be reliably quantified with CT. After 20 weeks, the CT-determined mean calcium volume was 1831 ± 581 mm³, with a mean wall calcium content of 89.8 ± 44.4 μg/mg (r² = 0.68). In stented pericardial valves implanted in mitral position, reliable determination of tissue mineralization is disturbed by scattering caused by the (continuously moving) alloy of the stent material. Pericardial patches in the neck vessels revealed progressive mineralization, with a significant increase in mean HU and calcium volume at 8 weeks after implantation, rising up to a level of 131.1 ± 39.6 mm³ (mean calcium volume score) and a mean calcium content of 19.1 ± 12.3 μg/mg. Conclusion. The process of bioprosthetic tissue mineralization can be visualized and quantified in vivo using multislice CT scanning. This allows determination of the kinetics of tissue mineralization with intermediate in vivo evaluations.

ECM-based materials in cardiovascular applications: Inherent healing potential and augmentation of native regenerative processes

The in vivo healing process of vascular grafts involves the interaction of many contributing factors. The ability of vascular grafts to provide an environment which allows successful accomplishment of this process is extremely difficult. Poor endothelisation, inflammation, infection, occlusion, thrombosis, hyperplasia and pseudoaneurysms are common issues with synthetic grafts in vivo. Advanced materials composed of decellularised extracellular matrices (ECM) have been shown to promote the healing process via modulation of the host immune response, resistance to bacterial infections, allowing re-innervation and reestablishing homeostasis in the healing region. The physiological balance within the newly developed vascular tissue is maintained via the recreation of correct biorheology and mechanotransduction factors including host immune response, infection control, homing and the attraction of progenitor cells and infiltration by host tissue. Here, we review the progress in this tissue engineering approach, the enhancement potential of ECM materials and future prospects to reach the clinical environment.

Stentless valves treated by the L-hydro process in the aortic position in sheep

Calcification of glutaraldehyde-treated bioprosthetic heart valves is a major cause of long-term failure. We studied porcine aortic valves treated by the L-Hydro process and implanted into 14 juvenile sheep (group 1). Another 10 sheep were implanted with glutaraldehyde-treated porcine bioprostheses (group 2). The animals were sacrificed after 150 days and the explanted valves were analyzed for calcification. Hemodynamic measurements by echocardiography and angiography were carried out prior to sacrifice. Macroscopic analysis showed calcification and loss of mobility of the leaflets in all group 2 implants and in one group 1 implant. Light microscopy showed foci of calcification in all group 2 implants and in 3 valves from group 1. A significant reduction in the level of calcification was found in porcine bioprostheses treated by the L-Hydro process and implanted into the juvenile sheep model.

An Intra-Aortic Shunt Prevents Paralysis During Aortic Surgery in Sheep

INTRODUCTION

Sheep are recommended by the United States Food and Drug Administration as a model for testing cardiovascular tissue, but are particularly prone to spinal cord ischemia and subsequent paralysis during aortic cross-clamping.

METHODS

A shunt consisting of a 9 cm long phosphorylcholine coated 1/4 in. (i.d.) polyvinylchloride tube was inserted through the aortotomy into the aorta to provide blood flow across the operative site. Blood pressure and flow in the distal aorta were measured continuously with an indwelling femoral artery catheter and an ultrasonic aortic flow probe. The hemodynamic effects were measured in seven 45 to 55 kg Suffolk sheep. This shunt was then used to implant decellularized pulmonary artery patches into 25 animals.

RESULTS

Occlusion of the aorta reduced the distal mean aortic pressure from 86.4 +/- 4.6 mmHg to 1.79 +/- 0.4 mmHg (P < 0.001) and opening the intra-aortic shunt restored the distal mean aortic pressure to 67.9 +/- 7.3 mmHg (P = 0.053). Blood flow in the distal aorta was 2.35 +/- 0.37 L/min at baseline and was reduced to -0.01 +/- 0.01 L/min (P < 0.001) with the aorta cross-clamped and returned to 2.49 +/- 0.36 L/min (P = 0.945) when the shunt was opened. Use of this shunt prevented hind leg paralysis in all 24 animals surviving the procedure.

CONCLUSIONS

A simple intra-aortic shunt was effective in restoring blood pressure and flow in the aorta distal to the operative site and prevented hind leg paralysis associated with aortic clamping.

Inbred or outbred? An evaluation of the functional allogenicity of farm sheep used in cardiac valve studies

OBJECTIVE

Cryopreserved allograft cardiovascular tissue elicits a strong cellular and humoral response in recipients; this may accelerate the deterioration of the allograft and complicate future heart transplantation. Juvenile sheep are the standard model for in vivo valve research and have been used to investigate the allogeneic immune response to cardiac valve and vascular tissue transplantation. Studies to date have not considered the extent of allogenicity of sheep used in transplantation studies.

METHODS

Functional allogenicity was assessed by standard one-way mixed lymphocyte reaction assay using peripheral blood mononuclear cells. Responder cells were stimulated with irradiated stimulator cells and cultured at 37 degrees C in 95% air and 5% carbon dioxide for 3, 4, 5, and 6 days. Cultures were pulsed with tritiated thymidine for 24 hours and harvested onto filtermats.

RESULTS

The allogeneic response, measured as counts per minute, demonstrated a bimodal distribution. Fifty-nine (36.9%) of 160 pairs fell within the first peak (counts per minute < 10,000) and were defined as weak responders. The remaining 101 (63.1%) of 160 pairs of animals demonstrated a strong allogeneic response (counts per minute > or = 10,000) that followed a normal distribution.

CONCLUSIONS

More than 1 in 3 pairs of sheep is too closely related to elicit an immune response when cross-reacted. This finding may alter the interpretation of studies that base their findings on allogeneic transplantations in sheep without ascertaining the genetic similarities of the animals. Valve transplantation studies in a sheep model should assess the extent of allogenicity of donor and recipient sheep.

Decellularized Xenogenic Heart Valves Reveal Remodeling and Growth Potentialin Vivo

We have developed an advanced tissue processing technique on porcine pulmonary heart valves for pulmonary valve replacement and its initial clinical application during the autograft operation according to Ross. The novel concept consists of a cell-free matrix achieved by deoxycholic acid treatment that is repopulated by host cells in vivo. Molecular biology, radioligand binding, and electron microscopy consistently showed that these valves are almost free of cellular components. Animal experiments and clinical investigations revealed excellent hemodynamic properties of the valves, no need for antithrombotic therapy, and repopulation by host cells without any signs of calcification. In juvenile sheep the internal diameter of the implanted valves significantly increased in growing animals by approximately 10 mm. The repopulation of the decellularized heart valves was found not only in sheep but also in humans, which indicates that the underlying mechanisms, presumably repair mechanisms, might be common in mammals. If these findings can be confirmed by others, they will lead to new concepts in the field of cardiovascular tissue engineering that will eliminate the need for in vitro construction of autologous heart valves.

Factors influencing calcification of cardiac bioprostheses in adolescent sheep

OBJECTIVE

We determined the possible effects of age, antimineralization treatments, circulatory implant conditions, prosthesis design, and valve-related structural aspects on valve calcification in adolescent sheep.

METHODS

Calcium content was measured by means of atomic absorption spectrometry in bioprostheses implanted in 120 sheep (age <1 year) for a period of 3 or 6 months.

RESULTS

Bioprostheses calcified significantly in adolescent sheep, but the extent of calcification was multifactorial. Multivariate analysis of the calcium content reveals that age, mitral or pulmonary implant position, prosthesis design (stented or stentless), structure (porcine or pericardial, wall portion or cusp), and antimineralization treatment are independent factors influencing calcification; implant duration beyond 3 months was not. In juvenile sheep (age 5 months) the wall portion, as well as the cusps of the prosthesis, calcified significantly more than in adolescent sheep (age 11 months). Irrespective of age, the cusps of valves implanted in the mitral position calcified more than those in the pulmonary position. The wall portion of stentless valves calcified more than that of stented valves, and pericardial valves calcified less than porcine valves. The surfactant (Tween 80, No-React, and alpha-amino-oleic acid) and alcohol (ethanol and octanediol) treatment significantly reduced cusp calcification; sodium dodecylsulfate did not. None of the anticalcification treatments was able to prevent wall calcification in stentless porcine valves.

CONCLUSION

These findings suggest that tissue valve calcification is determined by many independent factors, which can be identified by using adolescent sheep as a preclinical in vivo model.

Prevention of Calcification of Bioprosthetic Heart Valve Cusp and Aortic Wall With Ethanol and Aluminum Chloride

BACKGROUND

Calcification is frequently associated with device failure of bioprostheses fabricated from either glutaraldehyde pretreated porcine aortic valves or bovine pericardium. It was hypothesized that differential pretreatment with ethanol-aluminum chloride will prove safe and efficacious for inhibiting the calcification of both the porcine aortic valve bioprosthetic cusp and the aortic wall.

METHODS

Glutaraldehyde-fixed porcine aortic valves were subjected to differential aluminum chloride (AlCl3) and ethanol pretreatment; aortic wall segments were treated exclusively with AlCl3 (0.1 moles/L) for 45 minutes, 6 hours, or 8 hours (groups 3A, B, and C, respectively), followed by valve cusp incubations in ethanol (80%, pH 7.4). Nontreated control bioprosthetic valves were either stent-mounted porcine aortic valve bioprostheses (Carpentier-Edwards, group 1) (Edwards, Santa Anna, CA) or St. Jude Toronto SPV valves (St. Jude Medical, St. Paul, MN) (group 2). Mitral valve replacements were carried out in juvenile sheep for 150 days.

RESULTS

Calcium in cusps from group 3A was 2.84 +/- 0.62 mg calcium/g tissue versus control, 22.79 +/- 8.46 mg calcium/g tissue, p = 0.04. Valves pretreated with AlCl3 for 45 minutes, 6 hours, and 8 hours had significantly lower levels of calcium in the aortic wall compared to controls (40.38 +/- 5.66, 26.77 +/- 4.02, and 28.94 +/- 8.25 mg calcium/g tissue for groups 3A, 3B, and 3C, respectively, vs 95.47 +/- 17.14 mg calcium/g tissue for group 1, p < 0.001, and 133.42 +/- 3.96 mg calcium/g tissue for group 2, p < 0.001).

CONCLUSIONS

Differentially applied ethanol and aluminum chloride pretreatment significantly inhibited calcification of both the glutaraldehyde-fixed porcine aortic valve bioprosthetic cusp and the aortic wall.

Modified stentless porcine valve enhances accelerated cuspal calcification in the juvenile sheep model

OBJECTIVE

Stent mounting of any bioprosthesis, induces a loss of mobility and reduces the effective valve orifice. By contrast, for stentless procedures, the higher surgical technicality remains a major obstacle for many surgeons. In an attempt to facilitate the insertion of the stentless porcine aortic valve (Toronto SPV), we tried to alter the design by lowering the invasive profile at the depth of the sinuses on both coronary sites. This could theoretically facilitate the implant of the modified stentless valve with an easygoing single layer suture at the challenging subcoronary level and make it more attractive for every surgeon.

METHODS

Modifications of the standard model were done by lowering the profile at the depth of the sinuses on both coronary sites, whether by plication or excision of the protruding porcine aortic wall at the nadir of each coronary sinus. Nine juvenile sheep underwent implantation of stentless porcine aortic valves in pulmonary position: 3 standard Toronto SPV, 3 plicated Toronto SPV and 3 excised Toronto SPV. In each series, valves were explanted after 3 months. Valves were analyzed.

RESULTS

The cusps of standard Toronto SPV were perfectly functioning and pliable, without visible calcification after three months. The calcium content of the cusps was less than those in the plicated and excised Toronto SPV (2.4 +/- 0.7 microg/mg versus 10.8 +/- 5.9 and 6.7 +/- 3.4 microg/mg). In the plicated and excised valves, calcification of the cusp was more pronounced in the commissural region (3.9 +/- 1.9, 29.0 +/- 16.7, 13.8 +/- 9.5 microg/mg in the standard, plicated and excised Toronto SPV, respectively). On the other hand, the aortic wall from the plicated Toronto SPV had more calcium than that from the other groups (53.6 +/- 6.3, 41.2 +/- 7.1, 45.2 +/- 7.4 microg/mg in the plicated, standard and excised Toronto SPV, respectively).

CONCLUSIONS

The modification of stentless porcine valve enhanced accelerated cuspal calcification in the commissural region. It accentuated that the correct implantation technique for stentless procedures is extremely important in order to prevent early degeneration.

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.

Calcification resistance with aluminum-ethanol treated porcine aortic valve bioprostheses in juvenile sheep

BACKGROUND

Calcification of glutaraldehyde fixed bioprosthetic heart valve replacements frequently leads to the clinical failure of these devices. Previous research by our group has demonstrated that ethanol pretreatment prevents bioprosthetic cusp calcification, but not aortic wall calcification. We have also shown that aluminum chloride pretreatment prevents bioprosthetic aortic wall calcification. This study evaluated the combined use of aluminum and ethanol to prevent both bioprosthetic porcine aortic valve cusp and aortic wall calcification in rat subcutaneous implants, and the juvenile sheep mitral valve replacement model.

METHODS

Glutaraldehyde fixed cusps and aortic wall samples were pretreated sequentially first with aluminum chloride (AlCl3) followed by ethanol pretreatment. These samples were then implanted subdermally in rats with explants at 21 and 63 days. Stent mounted bioprostheses were prepared either sequentially as previously described or differentially with AlCl3 exposure restricted to the aortic wall followed by ethanol pretreatment. Mitral valve replacements were carried out in juvenile sheep with elective retrievals at 90 days.

RESULTS

Rat subdermal explants demonstrated that sequential exposure to AlCl3 and ethanol completely inhibited bioprosthetic cusp and aortic wall calcification compared with controls. However the sheep results were markedly different. The differential sheep explant group exhibited very low levels of cusp and wall calcium. The glutaraldehyde group exhibited little cusp calcification, but prominent aortic wall calcification. All sheep in the two groups previously described lived to term without evidence of valvular dysfunction. In contrast, animals in the sequential group exhibited increased levels of cusp calcification. None of the animals in this group survived to term. Pathologic analysis of the valves in the sequential group determined that valve failure was caused by calcification and stenosis of the aortic cusps.

CONCLUSIONS

The results clearly demonstrate that a combination of aluminum and ethanol reduced aortic wall calcification and prevented cuspal calcification. Furthermore, this study demonstrates that exclusion of aluminum from the cusp eliminated the cuspal calcification seen when aluminum and ethanol treatments were administered in a sequential manner.

Valved jugular vein segments for right ventricular outflow tract reconstruction in young sheep

OBJECTIVE

This study was undertaken to investigate the degeneration and calcification of valved bovine jugular vein segments for right ventricular outflow tract reconstruction in juvenile sheep.

METHODS

Seven valved bovine jugular vein conduits (Contegra model 220; VenPro Corporation, Irvine, Calif) and 3 control conduits (MH100; Medtronic, Inc, Minneapolis, Minn) were implanted in the pulmonary artery in young sheep. After 20 weeks the conduits were explanted and qualitatively analyzed by epicardial echocardiography, gross examination, x-ray analysis, light microscopy, and transmission electron microscopy. Calcification was determined quantitatively by flame atomic absorption spectrometry.

RESULTS

Two Contegra conduits could not be analyzed because of endocarditis. All other Contegra conduits functioned well, with preserved structure and minimal calcification. The control MH100 conduits exhibited extensive fibrous sheathing, with calcification of the aortic wall portion and the commissural part of the Hancock valve.

CONCLUSIONS

The Contegra conduit's performance was clearly superior to that of the control MH100 conduit when implanted in the pulmonary artery position in juvenile sheep for 5 months.

Tissue engineering of an auto-xenograft pulmonary heart valve

To improve the durability of stentless valves without losing their excellent hemodynamic function, a new-generation auto-xenograft was developed and evaluated. A piece of vein was harvested from 3 juvenile sheep 6 weeks before implantation of the valve. Endothelial cells from the vein material were cultivated and used to reendothelialize a decellularized porcine pulmonary valve. The tissue-engineered valve was implanted into the right ventricular outflow tract of the juvenile sheep. It was explanted after 100 days and assessed macroscopically as well as by x-ray, light microscopy (hematoxylin and eosin staining and von Kossa staining), and scanning electron microscopy. Calcium content of the cusps was determined quantitatively by atomic absorption spectrometry. The sheep implanted with the valve recovered quickly without any problems during the observation period. X-ray examination of the 3 explanted valves showed no cusp calcification, which was confirmed by histological study. Atomic absorption spectrometry showed low tissue calcium content. A clinical safety and feasibility trial with an allograft valve prepared the same way showed excellent short-term results in 6 patients.

Aluminum chloride pretreatment of elastin inhibits elastolysis by matrix metalloproteinases and leads to inhibition of elastin-oriented calcification

Calcification of elastin occurs in many pathological cardiovascular diseases including atherosclerosis. We have previously shown that purified elastin when subdermally implanted in rats undergoes severe calcification and aluminum chloride (AlCl(3)) pretreatment of elastin inhibits calcification. In the present study we investigated whether matrix metalloproteinase (MMP) binding to elastin and elastin degradation is prevented by AlCl(3) pretreatment. Subdermal implantation of AlCl(3)-pretreated elastin showed significantly lower MMP-9 and MMP-2 activity surrounding the implant as compared to the control implants. AlCl(3) pretreatment also significantly inhibited elastin implant calcification at the seven-day implant period (AlCl(3)-pretreated 4.07 +/- 1.27, control 23.82 +/- 2.24 microg/mg; p<0.0001). Moreover, elastin gel zymography studies showed that gel pretreatment with AlCl(3) inhibited elastolysis by MMP-9. We also demonstrate significant suppression of MMP-2 activity in aortic wall segments of AlCl(3)-pretreated porcine bioprosthetic heart valve implants as compared to control valve implants in sheep mitral valve replacement studies. AlCl(3) pretreatment also significantly inhibited calcification of elastin in this model. Thus, we conclude that aluminum ion binding to elastin prevents MMP-mediated elastolysis and thus prevents elastin calcification.

Stentless bioprosthetic heart valve research: sheep versus primate model

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.

Calcification characteristics of porcine stented valves in a juvenile sheep model

BACKGROUND

Different antimineralization treatments of stented porcine bioprostheses were evaluated: ethanol (Epic), alpha-amino-oleic acid (AOA) (Mosaic), and sodium dodecyl sulfate (SDS) (Hancock II). A nontreated, glutaraldehyde-fixed valve (Labcor) served as control.

METHODS

For each treatment, six valves were implanted in juvenile sheep in the pulmonary position. Valves were explanted after 3 and 6 months and examined macroscopically, by roentgenogram and light and transmission electron microscopy. Calcium content (microg/mg) was determined by atomic absorption spectrometry.

RESULTS

The Labcor valves revealed small calcium deposits in the cusps, although calcium content remained low (median value 0.4+/-0.8 microg/mg). SDS did not prevent cusp calcification as assessed by histology and calcium content measurement, which was higher than in all other valves: 1.9+/-4.6 microg/mg (p < 0.05). Cusp retraction and rupture were occasionally found in the Hancock. The Mosaic and Epic valves showed no cusp calcification and had low calcium contents (0.3+/-2.4 microg/mg and 0.7+/-0.6 microg/mg, respectively). Epic showed less pannus formation, but had hematoma or iron staining in the cusps.

CONCLUSIONS

SDS is inefficient as an antimineralization treatment, in contrast to ethanol or AOA. Cusp hematoma after ethanol treatment needs further investigation.

Electron beam tomography for cusp calcification in homograft versus Freestyle xenografts

BACKGROUND

We have previously shown, by means of electron beam tomography, the pattern of calcification of the aortic root wall of homografts and porcine xenografts after aortic root replacement. However, application of similar methods for cusp calcification raises specific problems that have not been addressed before.

METHODS

A new method for localizing and quantifying calcification of the aortic valve cusps has been evolved. Intravenous contrast-enhanced electron beam tomography was introduced to visualize the aortic cusps. This technique was applied to quantify cusp calcification in 37 patients after aortic root replacement with a homograft (group H) or a Medtronic Freestyle valve (group F) at set intervals between 6 months and 2 years. A calcification score in Hounsfield units (HU) and a calcified volume score in cubic millimeters were calculated.

RESULTS

The aortic leaflets were clearly visualized in all patients. The mean calcium score in the cusps was 28.8+/-64.4 HU in group F and 62.4+/-66.9 HU in group H (p = not significant). The mean calcified volume score was 327.0+/-425.9 mm3 in group F and 642.0+/-443.0 mm3 in group H (p = not significant).

CONCLUSIONS

Contrast enhancement electron beam tomography is a useful tool for quantification of calcium in the aortic valve leaflets. Our preliminary results show a tendency toward more calcification in the homografts. This needs to be studied further in a bigger cohort of patients followed up for longer periods.

Influence of ischemic time and temperature on endothelial cell growth after transport

Background

The preparation of tissue-engineered material is a complex procedure. The possibility to transport tissue between laboratories without loosing endothelial cell (EC) function was examined.

Methods

In 3 month old juvenile sheep (n=6) a piece of vein (n = 14) was harvested and transported over 900 km to the tissue laboratory in Dulbecco's Modified Eagle's Medium (=DMEM). Vein material of each animal was transported at 4°C (Group I, n = 6) and 25°C (Group II, n = 8). EC growth potential was evaluated in function of the medium temperature and the ischemic time (between 8–24 hours). At the end of the first passage the EC of Group I and II were put together to save autologous serum of the sheep. After the 2nd passage the EC were cryopreserved at −80°C to evaluate if EC viability would change.

Results

The growth potential of hypothermic Group I was equal in 16.7% (n = 1), higher in 33.3% (n = 2) and lower in 50% (n = 3) than Group II which had the same ischemic time during transport. Increase in ischemic time up to 24 hours showed no decrease of growth potential. Cryopreservation had no significant influence on EC viability. Viability at the end of the second passage, after recultivation and at the end of the third passage was 97.4% ± 1.52, 95.5%±1.34 and 94.5% ± 1.08 respectively.

Conclusions

In sheep there is no need to transport the EC at a temperature of 4°C. Up to 24 hours growth potential and viability are maintained also at 25°C.

Calcification and degeneration characteristics of the Biocor no-react bovine internal mammary artery (BIMA) - in vivo evaluation in a sheep model

OBJECTIVE

The No-React process for biomaterials was suggested to prevent calcification and degeneration. We examined in vivo in a chronic sheep model the performance of a Biocor bovine internal mammary artery (BIMA) graft after No-React processing.

METHODS

'No-React' processing consists of aldehyde cross-linkage following a detoxification process with multiple physical variables and incubation with surfactant. Biocor BIMA No-React treated grafts have been interposed in the carotid artery in seven sheep with a Dacron graft as control. Grafts were explanted after 3 or 6months and were grossly examined, by X-ray, histology, transmission and scanning electron microscopy, and atomic absorption spectrophotometry.

RESULTS

In the BIMA, good healing was found with a smooth intimal surface, minimal inflammatory reaction, and a well preserved ultrastructure. Calcification increased progressively. In the Dacron grafts, a fibrous covering the inner surface and infiltration with fibroblasts, histiocytes and macrophages was noted. Calcium content was stable.

CONCLUSION

Calcification increased progressively in Biocor BIMA No-React grafts. Minimal inflammatory changes, a smooth inner surface and well preserved ultrastructure were noted.