Mitral valve replacement in the baboon (Papio ursinus) and the human with the University of Stellenbosch mitral valve prosthesis

To study the problem of thromboembolism that occurs following the use of prosthetic valves, the mitral valve was replaced in 20 Cape Chagma baboons with the University of Stellenbosch (U.S.B.) mitral valve prosthesis. In the absence of anticoagulants massive thrombus invariably formed on the metal portion of the prosthesis when the latter was left uncovered by material that allows for tissue ingrowth. Smooth, fairly well controlled tissue ingrowth occurred when the prosthetic ring was covered by Dacron velour material. Massive thrombus formation was never encountered although small fibrin thrombi, a potential source of emboli, became loosely attached to the Dacron velour covered prosthetic ring during the first eight post-operative weeks. Thereafter the smooth ingrowth of living tissue into the prosthesis appears capable of preventing thromboembolism. The clinical use of anticoagulants during the initial 3-4 post-operative months is recommended in view of our experimental findings and clinical experience of early embolism that occurred in 3 of 10 patients in whom the U.S.B. Dacron velour covered prosthesis was used in the absence of anticoagulants. This is the first reported study in which a sub-human primate was used to study the problem of thromboembolism associated with prosthetic valve replacement. The baboon can be highly recommended for this purpose.     

In Vitro Evaluation of a Novel Autologous Aortic Valve (Biovalve) With a Pulsatile Circulation Circuit

We have used in‐body tissue architecture technology to develop an autologous valved conduit with intact sinuses of Valsalva (biovalve). In this study, we fabricated three different forms of biovalves and evaluated their function in vitro using a mock circulation model to determine the optimal biovalve form for aortic valve replacement. A cylindrical mold for biovalve organization was placed in a dorsal subcutaneous pouch of a goat, and the implant that was encapsulated with connective tissue was extracted 2 months later. The cylindrical mold was removed to obtain the biovalve (16 mm inside diameter) that consisted of pure connective tissue. The biovalve was connected to a pulsatile mock circulation system in the aortic valve position. The function of the three biovalves (biovalve A: normal leaflets with the sinuses of Valsalva; biovalve B: extended leaflets with the sinuses of Valsalva; biovalve C: extended leaflets without the sinuses of Valsalva) was examined under pulsatile flow conditions using saline. In addition, the mock circuit was operated continuously for 40 days to evaluate the durability of biovalve C. The regurgitation rate (expressed as a percent of the mean aortic flow rate during diastole) was 46% for biovalve A but only 3% for biovalves B and C. The durability test demonstrated that even after biovalve C pulsated more than four million times (heart rate, 70 bpm; mean flow rate, 5.0 L/min; mean aortic pressure, 92 mm Hg), stable continuous operation was possible without excessive reduction of the flow rate or bursting. The developed biovalve demonstrated good function and durability in this initial in vitro study.     

An investigation of a compliant interface for press-fit joint replacement

Earlier in vitro studies showed that a compliant layer between a metal surface and trabecular bone improved the load distribution. In this study, the behavior of a compliant layer of Dacron velour was investigated in vivo using a patella resurfacing in a sheep as a model. Bilateral cases were used to compare the velour interface with a direct metal-to-bone interface. For the metal patellas, a fibrous layer developed adjacent to the metal while the underlying bone formed a new subchondral-like layer. With the velour interface, fibrous tissue invaded the velour, followed later by bone, which sometimes reached the metal surface. For follow-ups of 8 months or more, the load across the interface was transferred over localised patches, for both the press-fit and velour interfaces. There was no significant difference in the areas of contact. There was evidence that this was due to the irregularity of the bony surface beneath the fibrous layer, or to bone nodules actually growing up to the metal. It was concluded that in this in vivo model, the velour layer did not retain a more uniform load distribution compared with the press-fit joint, due to the nature of the bone and fibrous tissue that formed at the interfaces.     

Tissue engineering of heart valves: in vitro experiences

BACKGROUND: Tissue engineering is a new approach, whereby techniques are being developed to transplant autologous cells onto biodegradable scaffolds to ultimately form new functional tissue in vitro and in vivo. Our laboratory has focused on the tissue engineering of heart valves, and we have fabricated a trileaflet heart valve scaffold from a biodegradable polymer, a polyhydroxyalkanoate. In this experiment we evaluated the suitability of this scaffold material as well as in vitro conditioning to create viable tissue for tissue engineering of a trileaflet heart valve. METHODS: We constructed a biodegradable and biocompatible trileaflet heart valve scaffold from a porous polyhydroxyalkanoate (Meatabolix Inc, Cambridge, MA). The scaffold consisted of a cylindrical stent (1 x 15 x 20 mm inner diameter) and leaflets (0.3 mm thick), which were attached to the stent by thermal processing techniques. The porous heart valve scaffold (pore size 100 to 240 microm) was seeded with vascular cells grown and expanded from an ovine carotid artery and placed into a pulsatile flow bioreactor for 1, 4, and 8 days. Analysis of the engineered tissue included biochemical examination, enviromental scanning electron microscopy, and histology. RESULTS: It was possible to create a trileaflet heart valve scaffold from polyhydroxyalkanoate, which opened and closed synchronously in a pulsatile flow bioreactor. The cells grew into the pores and formed a confluent layer after incubation and pulsatile flow exposure. The cells were mostly viable and formed connective tissue between the inside and the outside of the porous heart valve scaffold. Additionally, we demonstrated cell proliferation (DNA assay) and the capacity to generate collagen as measured by hydroxyproline assay and movat-stained glycosaminoglycans under in vitro pulsatile flow conditions. CONCLUSIONS: Polyhydroxyalkanoates can be used to fabricate a porous, biodegradable heart valve scaffold. The cells appear to be viable and extracellular matrix formation was induced after pulsatile flow exposure.     

New practical sizer for ATS medical open pivot valve]

The sewing cuff of the ATS Medical valve is made from double velour polyester, making the sewing cuff diameter larger than the tissue anulus diameter of this prosthetic heart valve. The ATS valve sizer, with the diameter marked in millimeters, has a ring which allows for an easy measurement of the patient's tissue anulus. However, the diameters of this ring and the prosthetic valve (tissue anulus diameter) are made to equal in size. Therefore, if the valve size is determined by using this sizer, the sewing cuff diameter will be considerably larger than the patient's tissue anulus diameter. In order to also take into account the diameter of the sewing cuff, we added a flange around the sizer in the shape of the sewing cuff. The new and more practical sizer allows us to avoid sizing trouble in valve replacement surgery.     

组织工程骨膜异体体内成骨修复兔骨缺损的初步观察

目的探讨以兔BMSCs和猪SIS复合构建的组织工程骨膜，在异体兔体内成骨的可行性。方法取新西兰大白兔BMSCs与SIS复合构建组织工程骨膜。选2月龄新西兰大白兔12只，制备双侧桡骨1．5～2．0cm缺损模型。随机选一侧植入组织工程骨膜，作为实验组；另一侧仅植入单纯SIS，作为对照组。术后观察动物一般情况，4周后摄X线片观察，取骨缺损中段标本行HE及Masson染色观察。结果两组动物术后饮食及日常活动基本正常：伤口无红肿、溢脓等：伤肢基本能负重行走。x线片观察：实验组骨缺损处有长条状新生骨形成，密度与正常骨相同，新生骨桥接骨缺损；对照组骨缺损无骨形成征象，骨缺损处密度与周围软组织影相近。组织学观察：实验组骨缺损处有新骨形成，骨组织中可见血管腔及不规则髓腔样结构；未见明显异物巨噬细胞及淋巴细胞浸润征象：对照组骨缺损处仅为胶原瘢痕组织，无骨组织形成。结论以SIS和BMSCs构建的组织工程骨膜在同种异体体内可以成骨，有修复骨缺损的可行性。     

Viability of autologous fascia lata in heart valve replacements

A histological and radioautographic examination of 11 autologous fascia lata heart valves used in man is described. There was a significant decrease, exponential with time, in the number of fibroblasts per unit volume (P<0·001). The collagen bundles were grossly disorganized and separated, suggesting a breakdown of the cross-linkage in the tissue. Redundant connective tissue on the surface of the valve cusp became oedematous and contained many trapped cells. A pseudoendothelium was formed within 10 days. Incorporation of tritium-labelled thymidine in the nuclei of the fibroblasts showed a sixfold reduction over 9 to 12 weeks following implantation, suggesting a failure of metabolism in these cells. The suitability of fascia lata for human heart valve replacement is discussed.     

Operative indication for aortic valvuloplasty by rasping procedure from the point of histopathologic evaluation

Rasping procedure is proposed by the author as one of the methods of aortic valvuloplasty and defined as shaving the surface of rheumato-degenerative aortic valve by using the electric rasp. Materials were the removed rheumato-degenerative aortic valves as specimen, and classified into 3 groups. The first group (type I) was valve lesion limited to valve free edge, second (type II) was mild thickening entirely, third (type III) was severe thickening with calcified degeneration. Rasping procedure was performed for the thickened portion of the valve specimen by the electric rasp. Morphologic examinations after rasping procedure were evaluated by histopathologic study. Histopathologically, there was hyaline degenerative connective tissue in superficial layer above the collagen fiber's layer in rheumato-degenerative thickened valve in type I. This hyaline degenerative connective tissue was considered to be fragile and pathologic in the tissue structure. Rasping procedure could remove this connective tissue layer. Type II, there was the similar finding to the type I from the free edge to the mid portion of the cusp. So, Rasping procedure was effective for type I and type II valve degeneration. On the contrary, the calcified lesion (type III), rasping procedure was not effective in valve coaptation and the pathological findings showed the fragmentation in the calcified layer. In the pathological comparison with the slicing procedure for type II by the surgical knife, there was a crack and cleft in the collagen fiber's layer in the case of slicing procedure. It can be concluded the results of histopathological study of the rasping procedure proved to be superior to the conventional aortic valvuloplasty (slicing method).     

Seeding endothelium onto canine arterial prostheses. The effects of graft design.

To identify prosthetic characteristics that support the proliferation of an endothelial lining, 14 different graft designs were studied in dogs. The grafts were prepared by the use of a technique of endothelial seeding that we described previously. They were studied two and four weeks after their implantation. Weft-knit Dacron grafts (water porosity from 1,400 to 1,650 mL/min/sq cm) were the most successful. A velour index (velour stitch frequency times velour loop height) was computed. When the internal velour index (IVI) was greater than 60,000 loop-mu/sq cm, the percentage of clot-free surface was 17.2 +/- 14.5%, compared with 62.0 +/- 26.9% when the IVI less than 60,000 loop-mu/sq cm. Endothelium could be detected on 61.5% of the grafts when the IVI less than 60,00 loop-mu/sq cm, compared with 0% when the IVI greater than 60,000 loop-mu/sq cm. The cells that formed the outer capsule were better organized and more adherent to the graft when an external velour was present, but external velour did not affect the inner lining. We conclude that weft-knit Dacron grafts with water porosities from 1,400 to 1,650 mL/min/sq cm and with limited internal velour (IVI less than 60,000 loop-mu/sq cm) are suitable substrates for single-staged endothelial-cell seeding.     

Dacron velour arteriovenous fistula for hemodialysis access

Dacron velour arteriovenous fistulas were created in the necks of 12 dogs. Sham dialysis was performed three times per week for one month in six animals, and for six months in an additional six animals. One prosthesis became infected, and perigraft bleeding occurred twice. There were no false aneurysms, and all prostheses remained patent. Dacron velour appears to be a satisfactory prosthetic material for use as an arteriovenous fistula for chronic hemodialysis access. The enhanced fibrous tissue adherence of Dacron velour may account for the few complications encountered.     

Histopathology of the A1 pulley in adult trigger fingers

The histopathology of the central parts of 40 A1 pulleys from adult patients with primary trigger fingers was studied using light and transmission electron microscopes and the findings were compared with those in a control series of 10 normal A1 pulleys. The evaluation of the normal A1 pulley revealed a bi-laminar structure. The deepest layer was composed of dense normal connective tissue. The outermost layer was formed by loose connective tissue. In trigger digits, it was possible to identify a tri-laminar structure. The deepest layer was composed of irregular connective tissue, formed by small collagen fibres and abundant extracellular matrix. A considerable amount of chondroid-metaplasia was present in this layer. The middle layer contained dense, normal connective tissue with some fibrocytes. The outermost layer was formed of loose connective tissue. In conclusion, there was an additional layer in the A1 pulley in pathological cases which was not present in normal pulleys.     

Reoperation for a Starr-Edwards aortic valve implanted 28 years earlier

A 56-year-old man admitted with dyspnea had undergone aortic valve replacement using a Starr-Edwards ball valve to treat aortic regurgitation 28 years earlier. Chest radiography showed moderate cardiomegaly, moderate pulmonary edema, and mild pleural effusion. Echocardiographic examination showed severe mitral regurgitation. The mitral valve was replaced using a St. Jude Medical prosthesis, and the Starr-Edwards aortic valve was replaced using a CarboMedics prosthetic valve. The cloth covering on the Starr-Edwards valve had worn away and pannus had formed. The patient's postoperative course was uneventful, and he was discharged on postoperative day 35.     

Homologous dura mater cardiac valves. Study of 533 surgical cases.

A group of 533 patients had cardiac valves replaced with homologous dura mater valves. The dura mater was preserved in a solution of 98 per cent glycerol and antibiotics for a period of 12 days before used. The leaflets were mounted in a stainless steel ring covered by Dacron velour. Two hundred forty-five patients had mitral valve replacement; 205 patients, aortic valve replacement; 17 patients, tricuspid valve replacement; and 2 patients, pulmonary valve replacement. Sixty-four patients were subjected to multivalvular replacements. The patients were followed for a period of 1 to 40 months after surgery with satisfactory clinical and hemodynamic results. Because 2 patients developed endocarditis produced by fungii, fungicidal drugs were added to the preservative solution. No bacterial endocarditis has been observed. No pressure gradient through the valve has been noted at rest. Anticoagulant drugs have not been used in the postoperative period.     

Implications of late morphology of Braunwald-Cutter mitral heart valve prostheses

Interrelationships among silicone poppet wear, cloth wear, and tissue ingrowth were investigated in 14 retrieved Braunwald-Cutter heart valve prostheses following implantation of 37 to 118 (mean 83) months. Six aortic valves (mean 81 months) had severe cloth and poppet wear. In three the poppet had escaped. The lesser wear of the strut covering on the eight mitral valves (mean 84, range 37 to 108 months) was generally functionally insignificant. Mean decrease in mitral poppet diameter was 0.4% (range 0% to 1.5%), in contrast to a mean of 5.8% for aortic poppets. Histologic examination of the cloth/tissue complex demonstrated well-collagenized tissue ingrowth in areas of intact fabric with focal endothelial lining. Functionally trivial calcific deposits were often noted deep in the tissue coating, adjacent to cloth fibers or the strut metal. These results suggest that the mitral Braunwald-Cutter prosthesis need not be electively replaced without specific indication. A model is presented which explains the favorable clinical course demonstrated for mitral recipients and provides a rationale for the disparate clinicopathological behavior of mitral and aortic Braunwald-Cutter prostheses. Although inconsequential in this setting, the focal microcalcification noted in all mitral prostheses implanted for more than 72 months may have implications for the development of clinical cardiac assist devices for long-term application.     

Section of tissue or prosthetic valve. A five-year prospective, randomized comparison.

After considerable experience, controversy persists between the selection of a tissue or prosthetic valve. In order to provide a nonbiased comparison, we designed a prospective, randomized study in September of 1970. Ninety-nine consecutive patients with isolated primary single valve replacement were randomized to tissue or prosthetic valves. The Tissue Bank supplied homografts which were either mounted for mitral replacement or used as free grafts for patients with small aortic roots. Starr-Edwards clot-covered prostheses were used for comparison. There was an even distribution of patients by age, sex, valve lesion, and New York Heart Classification attesting to the accuracy of the random selection. Anticoagulants were used in 33 patients who had operative or embolic evidence of atrial cloth or else history of thromboembolism. Thirty-five patients have undergone postoperative catheterization. Causes of death and valve failure are presented on an actuarial basis. Death in the Starr-Edwards patient group was sudden or due to fabric wear with subsequent thromboembolism, hemorrhage, or infection. We conclude that the tissue valve is a better choice for valve replacement. While there is no significant functional or hemodynamic apparent difference between the tissue and prosthetic valve, there is improvement in patient morbidity and mortality rate with the use of homografts, particularly in the aortic position. The primary cause of complications in the homograft is tissue deterioration, and this problem has been markedly reduced with advent of glutaraldehyde fixation. No such advance in solving the problem of host incompatability with the prosthesis has been forthcoming.     

Reoperation for a Starr-Edwards ball valve prosthesis implanted in mitral position 31 years ago

The patient is a 61-year-old woman who had undergone mitral valve replacement with the Starr-Edwards cloth-covered ball valve 31 years ago. She had dyspnea on effort 1 month before admission. The echocardiography revealed mitral and tricuspid regurgitation. Re-replacement of the mitral prosthetic valve with an ATS valve and tricuspid annuloplasty were successfully performed without any complication. The cloth wear of the Starr-Edwards ball valve cage was recognized and no thrombus was found at operation. To our knowledge, there has been no such a reoperative case who underwent so long postoperative period after initial implantation of the Starr-Edwards ball valve in Japan. This experience made us realize again the importance of attention to the complications related to a prosthetic valve like a cloth wear during long-term follow-up for the Starr-Edwards ball valve.     

Connective tissue framework of the greater omentum

Tissue samples of the greater omentum were intraoperatively collected from 17 patients on whom laparotomy was performed for different indications. The connective tissue framework of the unstained omentum was investigated, using a stereomicroscope. Histological sections were prepared from large saw-cuts of the plastinated omentum. The greater omentum of man was found to possess a connective tissue framework with blood and lymphatic vessels and was also found to be embedded in adipose tissue. The latter is made up of fatty organs differentiated in size. Round to oval organs are formed by fat cells. These organs are delimitated from their environment by a tender connective tissue capsule and are connected, through a pedunculated structure, to a vascular cord of the connective tissue framework. Connective tissue fibres radiate from the framework into the capsule which is made up of a submesothelial connective tissue layer and the mesothelium. The peduncle of a fatty organ consists of connective tissue as well as of supplying blood and lymphatic vessels. Fatty organs surrounded by connective tissue fibres were visualised even in highly adipose regions by means of plastinated saw-cuts of the greater omentum.     

The influence of inner wall filamentousness on the performance of small- and large-caliber arterial grafts

Dacron prostheses with differing degrees of inner wall filamentousness were implanted in the canine descending thoracic aorta for 56 days (n = 14) and the carotid arteries for 21 days (n = 40). In the thoracic aorta the healed inner capsule of 8 mm internal velour grafts was approximately three times as thick as the inner capsule of external velour knitted prostheses. However, the early patency and rapidity of healing of these two types of prostheses were essentially the same. In the carotid arteries the patency of the 4 mm external velour prostheses was greater than that of the internal velour prostheses and the mean thrombus-free surface area of the external velour grafts was significantly greater than that of the internal velour grafts. These observations suggest that an internal velour surface is not deleterious to early patency in a large-caliber, high-flow artery but that it may be in a small-caliber, low-flow artery.     

Bone ingrowth in the presence of particulate polyethylene. Synergy between interface motion and particulate polyethylene in periprosthetic tissue response

We have investigated whether the presence of polyethylene (PE) alone is sufficient to cause an aggressive periprosthetic tissue response, or whether certain mechanical interface conditions can allow bone to grow while in the presence of PE. An experimental implant was loaded in the presence and absence of particulate PE under stable and unstable conditions. Bone with a thin, discontinuous fibrous membrane formed in both groups of stable implants, either in the presence or absence of PE. By contrast, a continuous fibrous membrane consistently formed in both groups of unstable implants. The membrane consisted of loose fibrous connective tissue when PE was absent, and dense connective tissue with macrophages and a synovial lining when PE was present. In this model, if the interface was stable, the presence of PE was not sufficient to prevent the formation of bone or to produce a phagocytic tissue response. Only when the interface was unstable did a fibrous membrane form, and only then in the presence of PE.     

Reoperation for a patient 25 years after a Starr-Edwards ball mitral valve was installed.

A 45-year-old female suffered from increasing dyspnea during exercise and edema of lower extremities from January 2000. She had undergone mitral valve replacement with Starr-Edwards ball prosthesis (model 6320) due to mitral valve regurgitation 25 years ago. The cardiac catheterization and echocardiography documented mitral, aortic and tricuspid valves regurgitation grade III. Left ventricular ejection fraction rate was 49% and the pressures of CVP, RA, RV and PA were also increased. Laboratory examination showed slight hemolytic anemia. Double valve replacement (ATS valve) and tricuspid annuloplasty were carried out in April 2000. Strut cloth wear was confirmed at operation. Her postoperative course was uneventful. We hereby review the published paper of all cases with an implanted Starr-Edwards ball valve who required redo valve replacement with over 15 years follow-up. We consider that cloth injury is the main cause for reoperation and it usually associated with hemolytic anemia; cloth wear not only involves the aortic position but also frequently involves the mitral position for over 15 years follow-up patients and can be corrected by reoperation. Cloth wear should be concerned for those surviving patients who have received the Starr-Edwards ball valve during long-term follow-up.