Bovine Pericardial Xenograft Research Articles

Duraplasty Type as a Predictor of Meningitis and Shunting After Chiari I Decompression

Expansile duraplasty is frequently performed during Chiari I decompression. Aseptic and bacterial meningitis are possible complications of this procedure. We sought to compare the rates of meningitis and subsequent need for cerebrospinal fluid (CSF) diversion with duraplasty using bovine pericardial (BPC) xenograft and allograft. We conducted a retrospective review of 112 patients who underwent Chiari I decompression. All patients underwent duraplasty with either allograft or BPC. Occurrence of postoperative lumbar punctures and associated data were recorded to determine rates of meningitis. Rates of subsequent shunting were also recorded. Overall, 112 patients were included in the study: 30 underwent duraplasty with allograft (27%) and 82 received BPC (73%). A total of 26 patients developed postoperative meningitis (23 cases of chemical meningitis and 3 of bacterial meningitis). Rates of meningitis were higher in patients who received BPC than patients who received allograft (28% vs. 10%, respectively; P= 0.047). The rate of shunting was greater in patients with meningitis compared with patients without meningitis (56.5% vs. 5.75%, respectively; P < 0.0001). Moreover, 13 of the 15 patients (87%) in the BPC cohort who were shunted were found to have meningitis compared with 0 of the 3 shunted patients (0%) in the allograft cohort (P= 0.044). We found that rates of total meningitis were greater in patients who underwent Chiari I decompression and duraplasty with BPC compared with an allograft. The rate of shunting was significantly higher for patients who developed meningitis after decompression compared with patients without meningitis.

“Less Stented” Bovine Pericardial Xenograft: A New Concept

The in vitro hemodynamic behavior of a bovine pericardium xenograft with discontinuity of the annular support, named the "Less Stented" bovine pericardial xenograft, was analyzed. A "Less Stented" bovine pericardial xenograft consisting of a glutaraldehyde-treated bovine pericardium prosthesis manufactured in Braile Biomédica Ltd, São José do Rio Preto, São Paulo, Brazil, was used according to the same protocols of the stented bioprosthesis manufacturer. Bovine pericardial xenografts were tested in a pulse simulator and analyzed in a cardiac simulator, with respect to the transvalvular gradient, regurgitant fraction and leakage volume, discharge coefficient, performance, and efficiency index. Analyses were performed by Pearson's correlation test and simple linear regression. The transvalvular gradients ranged between 6.37 and 11.62 mm Hg with a mean flow between 4.39 and 7.96 L/min, giving a good correlation (0.8291) on the regression curve with an increase in flow. The regurgitant fraction ranged between 10.95 and 17.94% and leakage volume between 4.49 and 7.87%. The discharge coefficient, performance, and efficiency index showed favorable behavior with the flow increase, with good correlation coefficient (0.9385, 0.9332, and 0.9024, respectively). The initial results of the "Less Stented" bovine pericardial xenograft size 25 analyses demonstrated a satisfactory in vitro performance. Evaluations of the hemodynamic performance of small size "Less Stented" bovine pericardial xenograft should be made to clarify the biological behavior of this new xenograft.

Biaxial mechanical/structural effects of equibiaxial strain during crosslinking of bovine pericardial xenograft materials

We have investigated the effect of biaxial constraint during glutaraldehyde crosslinking on the equibiaxial mechanical properties of bovine pericardium. Crosslinking of cruciate samples was carried out with: (i) no applied load, (ii) an initial 25 g (∼30 kPa) equibiaxial load, or (iii) an initial 200 g (∼250 kPa) equibiaxial load. All loading during crosslinking was done under a defined initial equibiaxial load and subsequently fixed biaxial strain. Load changes during crosslinking were monitored. Mechanical testing and constraint during crosslinking were carried out in a custom-built biaxial servo-hydraulic testing system incorporating four actuators with phase-controlled waveform synthesis, high frame-rate video dimension analysis, and computer-interfaced data acquisition. The paired biaxial stress–strain responses under equibiaxial loading at 1 Hz (before and after treatment) were evaluated for changes in anisotropic extensibility by calculation of an anisotropy index. Scanning electron microscopy (SEM) was performed on freeze-fractured samples to relate collagen crimp morphology to constraint during crosslinking. Fresh tissue was markedly anisotropic with the base-to-apex direction of the pericardium being less extensible and stiffer than the circumferential direction. After unconstrained crosslinking, the extensibility in the circumferential direction, the stiffness in the base-to-apex direction, and the tissue’s anisotropy were all reduced. Anisotropy was preserved in the tissue treated with an applied 25 g load; however, tissue treated with an applied 200 g load became extremely stiff and nearly isotropic. SEM micrographs correlated well with observed extensibility in that the collagen fibre morphology changed from very crimped (unconstrained crosslinking), to straight (200 g applied load). Biaxial stress-fixation may allow engineering of bioprosthetic materials for specific medical applications.

Effect of molecular structure of poly(glycidyl ether) reagents on crosslinking and mechanical properties of bovine pericardial xenograft materials

With the identification of the exacerbating effect of glutaraldehyde on calcification of heart valve materials, there exists a renewed interest in both alternative reagents and the effects of crosslinking on connective tissues. One potentially useful class of reagents are poly(glycidyl ether) compounds. We have examined 5 of these reagents with different molecular sizes and functionalities for their effects on mechanical properties and collagen denaturation (shrinkage) temperature. Samples of bovine pericardium were tested fresh or after 48 h fixation in one of the five compounds for denaturation temperature, stress-strain response, stress relaxation, plastic deformation, and fracture properties. Of the compounds tested, those with intermediate length backbones and 4 or 5 epoxide groups were most effective in producing intrahelical crosslinking and increased denaturation temperature over 48 h. However, in samples examined after 17 months of fixation, all reagents had equivalently increased the denaturation temperature. Examination of mechanical results revealed two distinct mechanisms for mechanical change. Observed shifting of the stress-strain curve to the right (due to shrinkage), increased plastic deformation, and some reduction of stress relaxation are all unrelated to denaturation temperature (and hence to changes in intrahelical crosslinking). An alternate mechanism, perhaps formation of intermolecular crosslinks may be responsible. Intrahelical crosslinking produces only lesser reductions in stress relaxation. Cross-comparison of reagents of differing molecular structure provides a useful tool toward increased understanding of the mechanical consequences of tissue crosslinking.

Anesthetic and Postoperative Protocols for a Canine Model of Reversible Left Ventricular Volume Overload

The purpose of this study was to develop anesthetic and postoperative methods that could be used in a canine model of reversible left ventricular volume overload (LVVO). LVVO was created by inducing mitral regurgitation (MR) in adult conditioned dogs. Using fluoroscopy, MR was induced by passing urologic grasping forceps into the left ventricle through a carotid artery and rupturing one or more chordae tendinea. Cardiac catheterization was performed after significant cardiac dysfunction developed (3 months after creation of MR) in order to collect data to confirm reduced contractile function. The MR was repaired by replacing the damaged valve with a bovine pericardial xenograft. Dogs were followed with sequential cardiac catheterizations to determine if the valvular replacement reversed the cardiac dysfunction. To develop this model, unique anesthetic and post-operative care protocols had to be instituted. In order not to exacerbate the existing cardiac dysfunction, a high dose narcotic anesthetic regimen using a sufentanil infusion at 9-13 microgram/kg h-1 was developed in association with cardiopulmonary bypass and hypothermia for the mitral valve replacement surgery. Intensive postoperative care protocols that involved major personnel and pharmaceutic interventions were necessary. Using our methods 11/17 dogs survived the procedure and were included in the protocol for study of mechanisms involved in reversal of cardiac dysfunction.

The bovine pericardial xenograft: II. Effect of tethering or pressurization during fixation on the tensile viscoelastic properties of bovine pericardium.

Our previous article suggested that control of the extensibility of aldehyde-fixed pericardium could be achieved by controlling shrinkage during fixation. Therefore, to prevent shrinkage, we have used sandpaper-lined plexiglass plates to clamp circular samples of bovine pericardium during fixation in glutaraldehyde, tethering them at their original dimensions. As well, we have applied transmural pressures of 50 or 100 mm Hg during fixation using a hydraulic column of glutaraldehyde solution. Strips cut at 0 degree, 30 degrees, 60 degrees, and 90 degrees to the base-to-apex cardiac direction have been examined for cyclic stress-strain response, stress relaxation, plastic deformation, and fracture behavior. Under physiological stresses, tethered and pressure-fixed materials were both nearly isotropic. Tethering during fixation produced a material with extensibility nearly identical to that of fresh tissue. Plastic deformation during cyclic loading was reduced below that seen in simple fixation while stress relaxation was unchanged. Pressure-fixation produced reduced extensibility similar to that produced in porcine aortic valve leaflets. Plastic deformation and stress relaxation were both markedly reduced. Pressure-fixation reduced the strain at fracture, but fracture behavior was otherwise unaffected. Tethering and pressure-fixation offer attractive means to control the mechanical behavior of bovine xenograft materials.

The bovine pericardial xenograft: III. Effect of uniaxial and sequential biaxial stress during fixation on the tensile viscoelastic properties of bovine pericardium.

Our previous two articles have shown that glutaraldehyde-fixed bovine pericardium is nearly isotropic, whether fixed without constraints, with tethering, or with pressure. In this study, we have used uniaxial stress during fixation to produce bovine pericardial material with marked tensile anisotropy. Rectangular and cruciate pericardial samples have been mechanically examined after one of four treatments: (i) fixation under 88-kPa uniaxial stress, (ii) fixation under 176-kPa uniaxial stress, (iii) 3 h of 176-kPa uniaxial stress in saline followed by 24-h fixation under the same stress, (iv) fixation under 176-kPa uniaxial stress followed by a second fixation under 176-kPa stress in a direction normal to the first. Strips of material were cut at 0 degree, 30 degrees, 60 degrees, and 90 degrees to direction of the initial stress, and tested for response to cyclic loading, stress relaxation, plastic deformation, and fracture properties. Fixation under uniaxial stress produced anistropy similar to that seen in porcine aortic valve leaflets; however, the overall extensibility of the material depended on the applied stress and the aspect ratio of the stressed sample. While loading in saline produced no change, the sequential biaxial stressing produced a reduction in anisotropy, suggesting exposure of additional crosslinking sites. Uniaxial stress during fixation may be a useful method for construction of anisotropic heart valve leaflets.

Ten-year experience with pericardial xenograft valves

Five hundred fifty-three pericardial xenografts were inserted in 520 patients during a 9-year period at the Fu Wai Hospital in Beijing. The bovine pericardial xenograft was modeled after a similar type of prosthesis manufactured by Shiley Inc. (Irvine, Calif.). The late mortality rate in this series was only 1.8% per annum and the actuarial survival rate was 73.0% +/- 12% at 10 years. There was a very acceptable low incidence of thromboembolism of 0.41% per annum without the need for permanent anticoagulation. This is similar to the clinical reports with other tissue valves. The main question is the durability of the tissue prosthesis or, in other words, the freedom from valve-related clinical complications. In this series, the expected actuarial valve durability rate was 75.0% +/- 8.8% at 10 years. Whether this will continue to hold up over the next follow-up period is unclear. Certainly other tissue prostheses have shown significant degeneration rates beginning after the sixth year that have risen progressively thereafter. In any case, given the relatively low probability of thromboembolic phenomenon without anticoagulation, the trade-off of a prosthesis that may not be as durable as the mechanical ones is certainly acceptable.

Frequency analysis of Ionescu-Shiley prosthetic closing sounds in patients with normally functioning prostheses.

To document the frequency distribution of lonescu-Shiley (IS) bovine pericardial xenograft valve sounds, a study was conducted on three groups of clinically stable subjects with valves implanted for less than 5 years. These groups consisted of 61 subjects with aortic IS valves, 28 subjects with mitral IS valves and 18 subjects with mitral Hancock porcine xenograft valves. Multiple comparisons with a Scheffe with mitral Hancock porcine xenograft valves. Multiple comparisons with a Scheffe test at level a=0.01 showed that the spectral characteristics of closing sounds produced by normal IS and Hancock xenografts implanted in the mitral position were both significantly different from those of IS xenografts implanted in the aortic position but not significantly different from each other. In addition, the spectral distribution of IS closing sounds was highly reproducible and very slightly affected by the duration of the implant up to 5 years.

Autologous pericardium versus a xenograft substitute in myocardial wound healing

This study compared repair of myocardial wounds covered with autologous pericardium to healing of wounds covered with gluteraldehyde-preserved bovine pericardium in an experimental canine model. Right (RV) and left (LV) full thickness ventriculotomies were made and closed. In the control group ( n = 12), the pericardium was closed over the wound; in the experimental group ( n = 12), wounds were covered with bovine pericardium. Animals were sacrificed at 14, 21, 28, and 42 days. After excising the pericardium, 6 mm punch biopies of normal RV, RV wound, normal LV, and LV wound were assayed for hydroxyproline (HPro). Both autologous and bovine pericardium became densely adherent to the wounds. Bovine pericardium was mildly adherent over unwounded areas, while autologous pericardium was usually free. Normal RV contained more than twice as much HPro as normal LV (5.4 ± 0.57 μg/mg vs 1.7 ± 0.35 μg/mg, P < 0.0002). A gradual rise in HPro over time was seen in both groups, but this increase was statistically significant only at 42 days ( P < 0.05). There was no significant difference in HPro between wounds covered with autologous pericardium and those covered with bovine grafts ( P = 0.13) at any of the sample times in this study. In this experimental canine model, the pericardium does not appear to play a prominent role in myocardial wound healing by contributing collagen-producing fibroblasts. Furthermore, the bovine pericardial xenograft becomes densely adherent to LV and RV incisions. In the clinical setting, such may make reoperation more hazardous when the heart has been previously incised or coronary bypass grafts have been constructed.

Prevention of retrosternal adhesions after pericardiotomy

Because repeat sternotomies are becoming much more prevalent with repeat coronary bypass operations, prevention of direct adhesions of the heart and grafts to the back of the sternum by use of synthetic or xenograft material to close the pericardiotomy has become a matter for investigation. In this study bovine and equine glutaraldehyde-processed xenografts were implanted bilaterally in dogs for implant intervals of 6 weeks and 3, 6, 9, and 12 months. The bovine and equine xenografts both performed well in resisting the adhesion of the heart to their inner surfaces and less well in resisting adhesion of the lung and chest wall to their outer surfaces. The bovine xenograft had a higher percentage of adhesion-free surface on all the surfaces evaluated; however, one of our 12-month bovine pericardial xenograft implants exhibited significant multifocal calcific degeneration. Although pericardial xenografts generally have performed well when implanted in the dog, Gallo, Artiñano, and Duran recently expressed concern about their performance in humans. Along with our finding of calcification, their concern suggests a cautious approach to clinical application.

Two-dimensional echocardiographic assessment of complications involving the ionescu-shiley pericardial valve in the mitral position

The function of the Ionescu-Shiley bovine pericardial xenograft in the mitral position was investigated in 70 patients by two-dimensional echocardiography. Echocardiographic data from 21 patients with suspected bioprosthetic dysfunction and 49 patients with normal clinical findings were analyzed in a double-blind fashion. Confirmation of cardiovascular status was obtained by means of cardiac catheterization, surgery, autopsy or other techniques in 19 of the 21 symptomatic patients. Two-dimensional echocardiography correctly evaluated bioprosthetic function in 98% of the patients. Six of the seven patients with proven xenograft dysfunction demonstrated echocardiographic evidence of malfunction. There was one false negative evaluation but no false positive results. Valve dysfunction included endocarditic mass lesions, mitral regurgitation resulting from dehiscence of a leaflet or the sewing ring or mitral stenosis due to calcification or malposition of the valve. This experience indicates that two-dimensional echocardiography is useful for assessing the Ionescu-Shiley mitral bioprosthesis, particularly in those patients who develop nonspecific symptoms.

僧帽弁位に用いたIonescu-Shiley(IS)弁の弁サイズによる術後血行動態の検討

僧帽弁位に用いたIonescu-Shiley(IS)弁の弁サイズによる術後血行動態の検討