A Bioreactor with Compliance Monitoring for Heart Valve Grafts

The drawbacks of state-of-the-art heart valve prostheses lead researchers to explore the prospect of using tissue-engineered constructs as possible valve substitutes. It is widely accepted that the mechanical properties of the construct are improved with mechanical stimulation during in vitro growth. We designed a new dynamic bioreactor with the perspective of using decellularized valve homografts as scaffolds in order to produce tissue-engineered valve substitutes. The design guidelines were (a) compatibility with the procedures for the treatment of homografts; (b) delivery of finely controlled pulsatile pressure loads, which induce strain stimuli that may drive cells toward repopulation of and integration with the natural scaffold; and (c) monitoring the construct’s biomechanical status through a comprehensive index, i.e., its compliance. The handling needs during the set-up of the homograft and the use of the bioreactor were minimized. The bioreactor and its automated control system underwent tests with a compliant phantom valve. The estimated compliances are in good agreement with the measured ones. Tests were also carried out with porcine aortic samples in order to assess the hydrodynamic and biomechanical reliability. In the future, monitoring the construct’s compliance might represent a key factor in controlling the recellularization of the valve homografts, which provides awareness of the construct’s biomechanical status by real-time, non-destructive, and non-invasive means.     

Simultaneous morphological and stress-strain studies of the fibrous components in wet heart valve leaflet tissue.

Simultaneous morphological and stress-strain studies have been carried out on heart valve leaflet tissue maintained in its unaltered functional condition. A microtensile tissue testing device is described which inserts directly into the stage of an optical microscope fitted with a Nomarski interference contrast facility. Glutaraldehyde fixation of tissue subjected to different levels of loading reveals that the current stressed state of the collagen fibers is "frozen" in by crosslinking process, and as a consequence marked alterations in the preserved tissue properties are produced. This is shown to be relevant to the preparation of the glutaraldehyde treated heterograft heart valve. The mechanical roles of the collagen and elastin components are investigated and a "complementation" mechanism is postulated whereby the widely different mechanical properties of the two types of fibers are combined in a non-competing manner to produce a diversity of composite tissue characteristics.     

组织工程心脏瓣膜的构建：现状与前景

背景：目前临床上应用的心脏生物瓣和机械瓣都存在一些缺陷和不足,而组织工程心脏瓣膜有可能避免这些问题的出现,成为瓣膜替代物的理想选择。 目的：探讨构建组织工程心脏瓣膜的实验研究进展。 方法：应用数据库检索的方法分析关于组织工程心脏瓣膜的实验研究文献,组织工程心脏瓣膜的三大要素为种子细胞、支架材料和细胞种植。 结果与结论：心脏瓣膜修复和置换是目前治疗心脏瓣膜性疾病的主要外科手段。目前,主要用于构建组织工程心脏瓣膜的种子细胞有血管内皮细胞、内皮祖细胞以及骨髓间充质干细胞等。经脱细胞处理的支架具有良好的生物力学性能和组织相容性,细胞种植后支架表面会形成一层连续的细胞层,其构建的组织工程心脏瓣膜是可行的。组织工程心脏瓣膜有着良好的应用前景,但目前还有很多问题需要解决,还处于研究的初级阶段。 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程全文链接：     

Mechanical valve replacement in congenital heart defects in the era of international normalized ratio self-management

As the number of patients with congenital heart defects requiring heart valve replacement increases, the need for durable valve substitutes with good hemodynamic performance and a low incidence of complications becomes more apparent. The use of porcine xenografts is burdened with early fibrocalcific degeneration, whereas the use of mechanical heart valves led to an increased number of thromboembolic events, especially when implanted in the right side of the heart. We report on our experiences implanting bileaflet heart valves in congenital heart defects since the introduction of international normalized ratio (INR) self-management. The data of 68 long-term survivors (33 males, 35 females) who underwent mechanical heart valve replacement in congenital heart defect were reviewed. Patient age at the time of valve replacement ranged from 5 months to 61 years (mean 21 years). Underlying diagnoses were tetralogy of Fallot (n=33), morbus Ebstein (n=4), atrioventricular canal (n=13), truncus arteriosus communis (n=5), transposition of the great arteries (n=10), and congenitally corrected transposition of the great arteries (n=3). In all patients, bileaflet valves were implanted (St. Jude Medical n=40, Carbomedics n=28). Anticoagulation was performed using dicumarol (Marcumar) and INR self-management in all cases. The mean follow-up was 72 months (range 6-132 months; 409 patient-years). Valve thrombosis developed in 3 of 68 patients (4.4%, all three had tetralogy of Fallot, mean age 9.8 years) after a mean follow-up of 3.5 years. In two of these three patients, re-pulmonary valve replacement was necessary, whereas the third patient was treated by thrombolysis. From our experience, we conclude that mechanical heart valve replacement is a good therapy option with a low complication rate for patients with congenital heart defects requiring valve replacement, especially when INR self-management is performed.     

Daily transient discontinuation of extracorporeal LVAD to prevent thromboembolism of mechanical aortic valve prosthesis

Patients with mechanical aortic valves are generally contraindicated for left ventricular assist device (LVAD) insertion because the prosthetic valve often becomes fixed in closed position. A 41-year-old woman with mechanical aortic valve prosthesis experienced sudden chest pain and developed cardiogenic shock. A paracorporeal pulsatile LVAD and a monopivot centrifugal pump as a right VAD (RVAD) were implanted. The mechanical aortic valve was intentionally left in place. Soon after the operation, LVAD support was discontinued daily for few seconds to allow the mechanical aortic valve to open and to avoid thrombus formation. The patient was successfully weaned off RVAD and received anticoagulation therapy with warfarin. On postoperative day 141, she was transferred to a university hospital where a HeartMate II LVAD was implanted, and the aortic valve was successfully replaced with a bioprosthetic valve. The patient is currently awaiting heart transplantation.     

Axial flow pump support in a Marfan patient with an aortic mechanical heart valve: case report and literature review

The presence of a mechanical heart valve in the aortic position is usually considered a contraindication for the use of cardiac assist devices. Only a few cases with the combination of mechanical circulatory support and valve prostheses have been reported in the literature to date, and the experience is even more limited in the new generation of miniaturized axial flow pumps. We present a case report of a patient with a mechanical aortic heart valve who was successfully supported with a continuous flow pump and discuss the literature available on this problem. Further on, the patient was weaned from his ventricular assist device after 456 days of support.     

The first successful DeBakey VAD child implantation as a bridge to transplant

A 14-year-old boy with repaired transposition of the great arteries and ventricular septal defect presented with atrial flutter and severe congestive heart failure. Despite successful cardioversion and optimal medical therapy, the patient deteriorated and was supported with extracorporeal membrane oxygenation (ECMO). Two days after initiating ECMO support, we implanted the DeBakey VAD Child ventricular assist device (MicroMed Technology, Inc., Houston, TX) under the Humanitarian Device Exemption program. Later, he was able to pursue normal daily activities including physical rehabilitation and ambulation in the hospital. After 56 days, he underwent a successful cardiac transplantation. After 3 months, he had good cardiac function and no evidence of rejection. The DeBakey VAD Child device is a valuable option for cardiac support as a bridge to transplantation.     

纳米羟基磷灰石薄膜与人脐静脉血管内皮细胞的增殖

背景：合肥大学材料系和中国科学院安徽光学密精机械研究所联合研究应用脉冲激光沉积合成技术制备出一种新型的纳米羟基磷灰石人工心脏机械瓣膜。 目的：观察纳米羟基磷灰石人工心脏机械瓣膜与人脐静脉血管内皮细胞的相容性。 方法：将体外分离培养的传2-4代人脐静脉血管内皮细胞悬液接种于纳米羟基磷灰石人工心脏机械瓣膜上,培养3,7,21 d后,扫描电子显微镜下观察细胞在纳米羟基磷灰石人工心脏机械瓣膜上的生长情况。分别采用纳米羟基磷灰石人工心脏机械瓣膜常温浸提液、纳米羟基磷灰石人工心脏机械瓣膜高温浸提液、高密度聚乙烯浸提液及苯酚溶液培养人脐静脉血管内皮细胞,72 h后采用MTT法检测细胞增殖情况。 结果与结论：扫描电镜观察培养3 d时,人脐静脉血管内皮细胞呈梭形或多边形,伸出突起黏附于纳米羟基磷灰石人工心脏机械瓣膜上;7 d时,可见瓣膜表面细胞伸展充分,连接融合;21 d时,细胞成片融合,牢固覆盖于瓣膜表面,部分区域形成细胞外基质。MTT检测结果显示,纳米羟基磷灰石人工心脏机械瓣膜对人脐静脉血管内皮细胞无细胞毒性,具有良好的细胞相容性。中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程全文链接：     

Static and dynamic stresses during valve closure of a bileaflet mechanical heart valve prosthesis.

The effect of contact geometry and component compliance on the magnitude, distribution, and state of various types of stresses on a bileaflet mechanical heart valve prosthesis during valve closure was analyzed using an Edwards-Duromedics mitral valve as example. Static and dynamic stresses developing on both the leaflet and pivot ball during valve closure were modeled using finite element analysis (FEA). Uniform contact between the leaflet and housing as well as between the pivot ball and pivot slot can significantly reduce both static and dynamic stresses around the contact area. The level of the dynamic flexural stresses can be an order of magnitude higher than that of the static stresses. When both the radial and axial compliance of the housing are taken into consideration, peak dynamic stress was more than 40% less than that generated through the impact between a moving leaflet and a non-compliant rigid housing.     

Development of artificial neural network-based algorithms for the classification of bileaflet mechanical heart valve sounds

Objectives: As is true for all mechanical prostheses, bileaflet heart valves are prone to thrombus formation; reduced hemodynamic performance and embolic events can occur as a result. Prosthetic valve thrombosis affects the power spectra calculated from the phonocardiographic signals corresponding to prosthetic closing events. Artificial neural network-based classifiers are proposed for automatically and noninvasively assessing valve functionality and detecting thrombotic formations. Further studies will be directed toward an enlarging data set, extending the investigated frequency range, and applying the presented approach to other bileaflet mechanical valves. Methods: Data were acquired for the normofunctioning St. Jude Regent valve mounted in the aortic position of a Sheffield Pulse Duplicator. Different pulsatile flow conditions were reproduced, changing heart rate and stroke volume. The case of a thrombus completely blocking 1 leaflet was also investigated. Power spectra were calculated from the phonocardiographic signals and used to train artificial neural networks of different topologies; neural networks were then tested with the spectra acquired in vivo from 33 patients, all recipients of the St. Jude Regent valve in the aortic position. Results: The proposed classifier showed 100% correct classification in vitro and 97% when applied to in vivo data: 31 spectra were assigned to the right class, 1 received a false positive classification, and 1 was "not classifiable." Conclusion: Early malfunction detection is necessary to prevent thrombotic events in bileaflet mechanical heart valves. Following further clinical validation with an extended patient database, artificial neural network-based classifiers could be embedded in a portable device able to detect valvular thrombosis at early stages of formation: this would help clinicians make valvular dysfunction diagnoses before the appearance of critical symptoms.     

Stability and function of glycosaminoglycans in porcine bioprosthetic heart valves

Glycosaminoglycans (GAGs) are important structural and functional components in native aortic heart valves and in glutaraldehyde (Glut)-fixed bioprosthetic heart valves (BHVs). However, very little is known about the fate of GAGs within the extracellular matrix of BHVs and their contribution to BHV longevity. BHVs used in heart valve replacement surgery have limited durability due to mechanical failure and pathologic calcification. In the present study we bring evidence for the dramatic loss of GAGs from within the BHV cusp structure during storage in saline and both short- and long-term Glut fixation. In order to gain insight into role of GAGs, we compared properties of fresh and Glut-fixed porcine heart valve cusps before and after complete GAG removal. GAG removal resulted in significant morphological and functional tissue alterations, including decreases in cuspal thickness, reduction of water content and diminution of rehydration capacity. By virtue of this diminished hydration, loss of GAGs also greatly increased the "with-curvature" flexural rigidity of cuspal tissue. However, removal of GAGs did not alter calcification potential of BHV cups when implanted in the rat subdermal model. Controlling the extent of pre-implantation GAG degradation in BHVs and development of improved GAG crosslinking techniques are expected to improve the mechanical durability of future cardiovascular bioprostheses.     

Engineering analysis of the effects of bulging sinuses in a newly designed pediatric pulmonary heart valve on hemodynamic function

The purpose of this study was to examine the hemodynamic characteristics of expanded polytetrafluoroethylene (ePTFE) pulmonary valves with bulging sinuses quantitatively in a pediatric pulmonary mechanical circulatory system designed by us, in order to propose the optimal design for clinical applications. In this study, we developed a pediatric pulmonary mock circulation system, which consisted of a pneumatic right ventricular model, a pulmonary heart valve chamber, and a pulmonary elastic compliance tubing with resistive units. The hemodynamic characteristics of four different types of ePTFE valves and a monoleaflet mechanical heart valve were examined. Relationships between the leaflet movements and fluid characteristics were evaluated based on engineering analyses using echocardiography and a high-speed video camera under the pediatric circulatory conditions of the mock system. We successfully performed hemodynamic simulations in our pediatric pulmonary circulatory system that could be useful for quantitatively evaluating the pediatric heart valves. In the simulation study, the ePTFE valve with bulging sinuses exhibited a large eddy in the vicinity of the leaflets, whereas the straight tubing exhibited turbulent flow. The Reynolds number obtained in the valve with bulging sinuses was calculated to be 1667, which was smaller than that in the straight tubing (R (e) = 2454).The hemodynamic characteristics of ePTFE pediatric pulmonary heart valves were examined in our mock circulatory system. The presence of the bulging sinuses in the pulmonary heart valve decreased the hydrodynamic energy loss and increased the systolic opening area. Based on an in vitro experiment, we were able to propose an optimal selection of pulmonary valve design parameters that could yield a more sophisticated pediatric ePTFE valve shape.     

Aortic root compliance influences hemolysis in mechanical heart valve prostheses: an in-vitro study

Mechanical heart valve prostheses are known to activate coagulation and cause hemolysis. Both are particularly dependent on the leaflet dynamics, which in turn depends on the flow field in the aortic root influenced by the aortic root geometry and its compliance. Compliance reduction of large vessels occurs in aging patients, both in those who have atherosclerotic diseases and those who do not. In this study we investigated the correlation between hemolysis and the compliance of the proximal aorta in a novel, pulsatile in vitro blood tester using porcine blood. Two mechanical heart valves, the St Jude Medical (SJM) bileaflet valve and a trileaflet valve prototype (Triflo) were tested for hemolysis under physiological conditions (120/80 mm Hg, 4.5 l/min, 70 bpm) and using two different tester setups: with a stiff aorta and with a compliant aorta. Valve dynamics were subsequently analyzed via high-speed videos. In the tests with the Triflo valve, the free plasma hemoglobin increased by 13.4 mg/dl for the flexible and by 19.3 mg/dl for the stiff setup during the 3-hour test. The FFT spectra and closing speed showed slight differences for both setups. Free plasma hemoglobin for the SJM valve was up by 22.2 mg/dl in the flexible and 42.7 mg/dl in the stiff setup. Cavitation induced by the higher closing speed might be responsible for this, which is also indicated by the sound spectrum elevation above 16 kHz.     

Mechanical heart valve cavitation: valve specific parameters

Several aspects of mechanical heart valve cavitation, in particular of "severe" vapor cavitation, have been investigated in order to describe the phenomenon of cavitation itself and to classify various mechanical heart valves with respect to their tendency to cavitation. Furthermore, following the results of the measurements, a model for determination of time-dependent physical properties and dynamics of cavitation bubbles, such as size, pressure and temperature was developed. In order to classify the cavitation tendency of mechanical valves, a pulsatile hydraulic-driven circularly mock loop was used. Besides measurements of the relevant hemodynamic parameters, the leaflet velocities of the valves were also determined. In addition, numerous high-resolution pressure measurements, in particular the pressure drops necessary for the initiation of cavitation (local atrial pressure drop), were performed. For the investigation of bubble dynamics, a second pulsatile electro-magnetically-driven tester was used. The influence of density, viscosity and temperature of the fluid on the onset of cavitation was investigated. Cavitation events were recorded with a digital high-speed video camera (up to 40,500 frames/sec) for all investigated heart valves and under different conditions. A critical local upstream pressure drop (located within the model atrium after valve closure) of 450 mmHg was found for all valves as well as a valve specific correlation between left ventricular pressure gradient and local upstream pressure drop. Also, a valve dependent correlation between left ventricular pressure gradient and the local upstream pressure drop was provided. Finally, valve specific parameters were found to predict the cavitation tendency for a specific heart valve. The implementation of a suitable theoretical model allowed conclusions on bubble physics. High pressures (up to 800 bar) and temperatures (up to 1,300 degrees C) at bubble collapse have been determined. The influence of fluid parameters such as density, viscosity and temperature on the onset of cavitation is negligible within physiological range. Critical regions for cavitation for all mechanical heart valves were detected. All mechanical heart valves investigated show cavitation under different conditions (dp/dt) associated with high pressures and temperatures at bubble collapse. Cavitation bubble occurrence depends on valve design and location.     

Serious hemolytic anemia after mitral valvuloplasty

A patient with mitral insufficiency is described who developed severe hemolytic anemia six months after mitral valvuloplasty. Various laboratory tests suggested that the cause of the hemolysis was mechanical. A second heart operation was therefore performed which revealed intact valve function. With respect to the mechanical cause of hemolysis a bioprosthesis was implanted, but the patient died shortly after this operation. Since similar cases are not reported in the literature the authors invite for discussion of this case.     

Glycosaminoglycan entrapment by fibrin in engineered heart valve tissues

Tissue engineered heart valves (TEHVs) may provide a permanent solution to congenital heart valve disease by permitting somatic valve growth in the pediatric patient. However, to date, TEHV studies have focused primarily on collagen, the dominant component of valve extracellular matrix (ECM). Temporal decreases in other ECM components, such as the glycosaminoglycans (GAGs), generally decrease as cells produce more collagen under mechanically loaded states; nevertheless, GAGs represent a key component of the valve ECM, providing structural stability and hydration to the leaflets. In an effort to retain GAGs within the engineered constructs, here we investigated the utility of the protein fibrin in combination with a valve-like, cyclic flexure and steady flow (flex–flow) mechanical conditioning culture process using adult human periodontal ligament cells (PLCs). We found both fibrin and flex–flow mechanical components to be independently significant (p < 0.05), and hence important in influencing the DNA, GAG and collagen contents of the engineered tissues. In addition, the interaction of fibrin with flex–flow was found to be significant in the case of collagen; specifically, the combination of these environments promoted PLC collagen production resulting in a significant difference compared to dynamic and statically cultured specimens without fibrin. Histological examination revealed that the GAGs were retained by fibrin entrapment and adhesion, which were subsequently confirmed by additional experiments on native valve tissues. We conclude that fibrin in the flex–flow culture of engineered heart valve tissues: (i) augments PLC-derived collagen production; and (ii) enhances retention of GAGs within the developing ECM.     

Artificial valves “up to date” in Japan

We have many choices when selecting artificial valves for valve replacement surgery. It is necessary to know the characteristics of the various prosthetic valves to make an appropriate decision for each valvular heart disease patient. In this review paper, we describe the features and benefits of the artificial valves available in Japan. Standard and new generation bioprostheses and mechanical prostheses are reviewed. The new technology of the catheter-delivery heart valve is also mentioned in this paper.     

Mechanical valve replacement of the systemic atrioventricular valve in children

In children with systemic atrioventricular valve disease (SAVVD), reconstructive surgery is the primary goal. However, in cases with severely dysplastic valves or failed repair, valve replacement is the only option. The purpose of this study was to assess the early and late outcome following mechanical valve replacement in SAVVD. Between 1989 and 2003, 31 children underwent mechanical valve replacement (19 St. Jude Medical, 12 Carbomedics) in SAVVD (27 mitral, 3 tricuspid in corrected transposition of the great arteries, 1 common in an univentricular heart) at our institution. The ages ranged from 3 months to 15 years (mean 4 years) and body weight varied between 4.2 and 57 kg (mean 13.3 kg). The size of prostheses ranged between 16 and 31 mm (mean 23.9 mm). The main indication for valve replacement was severe insufficiency of left atrioventricular valve (84%); 84% of the patients had had a previous cardiac operation. The overall hospital mortality was 6.5% The mean follow up was 7.7 years (range 2-13 years). Ninety percent of children represent sinus rhythm, 87% are in NYHA class I. All patients were placed on a regimen of Phenprocoumon aiming to maintain the international normalized ratio (INR) between 3.0 and 4.0. Since 1994, INR self-management of oral anticoagulation was performed either by the patient or his or her parents. There was no anticoagulation-related complication in this patient group. Mechanical valve replacement in left atrioventricular valve disease carries a low operative risk across the spectrum of pediatric age despite previous operations in most cases. Long-term survival and quality of life are good in nearly all cases. The rate of anticoagulation-related complications is very low, especially when INR self management is performed.     

Mechanism for cavitation of monoleaflet and bileaflet valves in an artificial heart

It is possible that mechanical heart valves mounted in an artificial heart close much faster than those used for clinical valve replacement, resulting in the formation of cavitation bubbles. In this study, the mechanism for mechanical heart cavitation was investigated using the Medtronic Hall monoleaflet valve and the Sorin Bicarbon bileaflet valve mounted at the mitral position in an electrohydraulic total artificial heart. The valve-closing velocity was measured with a charge-coupled device (CCD) laser displacement sensor, and images of mechanical heart valve cavitation were recorded using a high-speed video camera. The valve-closing velocity of the Sorin Bicarbon bileaflet valve was lower than that of the Medtronic Hall monoleaflet valve. Most of the cavitation bubbles generated by the monoleaflet valve were observed near the valve stop; with the Sorin Bicarbon bileaflet valve, cavitation bubbles were concentrated along the leaflet tip. The cavitation density increased as the valve-closing velocity and the valve stop area increased. These results strongly indicate that squeeze flow holds the key to cavitation in the mechanical heart valve. From the perspective of squeeze flow, bileaflet valves with a low valve-closing velocity and a small valve stop area may cause less blood cell damage than monoleaflet valves.     

利用人骨髓基质干细胞构建组织工程心脏瓣膜的体外实验

BACKGROUND:Nowadays, mechanical or biological valve recipients used in the clinic are still at the risk of infection, hemorrhage, thrombosis and reoperation owing to valve stenosis. Tissue-engineered heart valve with biological activity can overcome the disadvantages above. While, the optimal choice of scaffolds and seeding cells remains disputable. OBJECTIVE:To explore the feasibility to construct tissue-engineered heart valve with acellularized porcine aortic valve scaffold and human bone marrow stromal stem cells in vitro. METHODS:The porcine aortic valves were decellularized with the detergent and enzymatic extraction process to remove the cellular components. Human bone marrow stromal stem cells were aspirated from sternum of the patients with simple congenital heart malformation, and then the cells were seeded on the acellularized porcine aortic valve scaffold and cultured for 5 days. RESULTS AND CONCLUSION:Flow cytometry identified that the characteristics of surface antigen of the inoculated seed cells were in line with those of human bone marrow stromal stem cells. Light microscopy and electron microscopy confirmed that the cellular components in the porcine aortic valves could be removed to obtain the complete acellular fiber mesh stent. There was no significant difference in biomechanical property between before and after acellularization. The human bone marrow stromal stem cells implanted on the acellularized porcine aortic valve scaffold could form a continuous cell layer on the surfaces of the scaffold. The inoculated bone marrow stromal stem cells could be differentiated into fibroblasts. The implantation of human bone marrow stromal stem cells on the acellularized porcine aortic valve scaffold can construct the tissue-engineered heart valve.