Heart Valve

In presence of aortic stenosis, a jet is produced downstream of the aortic valve annulus during systole. The vena contracta corresponds to the location where the cross-sectional area of the flow jet is minimal. The maximal transvalvular pressure gradient (TPG(max)) is the difference between the static pressure in the left ventricle and that in the vena contracta. TPG(max) is highly time-dependent over systole and is known to depend upon the transvalvular flow rate, the effective orifice area (EOA) of the aortic valve and the cross-sectional area of the left ventricular outflow tract. However, it is still unclear how these parameters modify the TPG(max) waveform. We thus derived an explicit analytical model to describe the instantaneous TPG(max) across the aortic valve during systole. This theoretical model was validated with in vivo experiments obtained in 19 pigs with supravalvular aortic stenosis. Instantaneous TPG(max) was measured by catheter and its waveform was compared with the one determined from the derived equation. Our results showed a very good concordance between the measured and predicted instantaneous TPG(max). Total relative error and mean absolute error were on average 9.4+/-4.9% and 2.1+/-1.1 mmHg, respectively. The analytical model proposed and validated in this study provides new insight into the behaviour of the TPG(max) and thus of the aortic pressure at the level of vena contracta. Because the static pressure at the coronary inlet is similar to that at the vena contracta, the proposed equation will permit to further examine the impact of aortic stenosis on coronary blood flow.

Background: Early prosthetic valve endocarditis is a serious life threatening infection of newly implanted prosthetic heart valve. A positive post-surgery heart valve culture is a significant risk factor for development of early prosthetic valve endocarditis.

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. 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. 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). 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.

The objective of this paper is to apply a new method in modeling and the hemodynamic characteristics for PCG-signals (phonocardiography), and examine the performance of spectral properties estimation through different blood flow pattern. The performance of efficient parametric ARMAX methods in estimating the spectral characteristics of mitral heart valve sounds. The parametric methods used were autoregressive (AR) techniques based on the wiener algorithm and linear predictive methods, an autoregressive-moving average with external input (ARMAX) technique based on wavelet decomposition, as well as delay inferometric method. Algorithms were tested on sounds obtained from patients with mitral regurgitation in mitral valve positions. Using these techniques, the spectrum produced by valvular regurgitation has been characterized and identified. This paper represents the new trends in PCG system identification. The paper also considers factors such as the suitability of predicting algorithms, implementation and integration of these algorithms, in an Auscultation Computer Aided Diagnosis (AuCAD), platform as well as the real time PCG Interpretation via optimal linear predictive methods.

Despite indications that GA (glutaraldehyde)-crosslinked tissues remain prone to long-term degradation and calcification, it is still the reagent of choice in the fixation of bioprosthetic heart valves. We have shown previously that increased GA concentrations and diamine extension of cross-links with lysine incorporation lead to mitigated in vivo calcification, mainly of porcine aortic-wall tissue. The present study was performed to assess the correlation between the cross-link density of all three commonly used tissue types [PW (porcine aortic wall), PL (porcine aortic leaflet) and BP (bovine pericardium)] and tissue calcification in the subcutaneous rat model after GA treatment with or without lysine. The effect of lysine enhancement, and increased GA concentration in the presence of lysine, resulted in significant increases in tissue cross-linking in all three tissue types. Although increased GA concentration on its own resulted in decreased calcification without an increase in cross-link density, overall positive correlations were found between denaturation temperature and RPD (resistance towards protease degradation) [correlation coefficient (ρ) values: ρ PW = 0.922, ρ PL = 0.783 and ρ BP = 0.955], whereas negative correlations existed between RPD and calcification (ρ PW = −0.836, ρ PL = −0.929 and ρ BP = −0.579). The combination of lysine enhancement and an increase in GA concentration from 0.2 to 3 % resulted in 79, 44 and 56 % decreases in calcification in PW, PL and BP. In the case of BP, a decrease in calcification of 81 % could be achieved merely by adding lysine extension to low-concentration (0.2 %) GA cross-linking. Thus it is concluded that the increase in cross-link density achieved by lysine incorporation, and by increased GA concentration in the presence of lysine, results in significant and marked decreases in calcification of all three types of tissues commonly used in bioprosthetic heart valves.

In nearly half of the heart valve replacement surgeries performed annually, surgeons prefer to implant bileaflet mechanical heart valves (BMHV) because of their durability and long life span. All current BMHV designs, however, are prone to thromboembolic complications and implant recipients need to be on a life-long anticoagulant medication regiment. Non-physiologic flow patterns and turbulence generated by the valve leaflets are believed to be the major culprit for the increased risk of thromboembolism in BMHV implant recipients. In this paper, we review recent advances in developing predictive fluid-structure interaction (FSI) algorithms that can simulate BMHV flows at physiologic conditions and at resolution sufficiently fine to start probing the links between hemodynamics and blood-cell damage. Numerical simulations have provided the first glimpse into the complex hemodynamic environment experienced by blood cells downstream of the valve leaflets and successfully resolved for the first time the experimentally observed explosive transition to a turbulent-like state at the start of the decelerating flow phase. The simulations have also resolved a number of subtle features of experimentally observed valve kinematics, such as the asymmetric opening and closing of the leaflets and the leaflet rebound during closing. The paper also discusses a future research agenda toward developing a powerful patient-specific computational framework for optimizing valve design and implantation in a virtual surgery environment.

Die kalzifizierte Aortenklappenstenose ist der häufigste Herzklappenfehler. Die Betroffenen sind ältere Menschen, die häufig zusätzlich Komorbiditäten wie linskventrikuläre Dysfunktion, eingeschränkte Nierenfunktion und pulmonale Hypertonie aufweisen. Das operative Risiko ist erhöht. Mit der perkutanen Aortenklappenvalvuloplastie können eine Symptomreduktion und Zunahme der Leistungsfähigkeit und damit eine bessere Lebensqualität erreicht werden; die Mortalität ändert sich dadurch nicht. Neue Techniken haben ein "Revival" dieser Methode, die vor 20 Jahren eingeführt wurde, ausgelöst. Auch die Brachytherapie der Aortenklappe nach Valvuloplastie ist jüngst unter-sucht worden und stellt einen interessanten Ansatz zur Reduktion der Restenose dar. Die Weiterentwicklung der Ballonvalvuloplastie ist der perkutane Klappenersatz, der derzeit in klinischen Studien angewandt wird. Neben dem antegraden/transseptalen bzw. retrograden Zugang wurde auch die Anwendung über eine transapikale Punktion des linken Ventrikels untersucht. Auch wenn Langzeitergebnisse noch ausstehen und die Prozeduren technischer Verbesserungen bedürfen, insbesondere einer Minimierung der notwendigen Kathetergrößen, ist mit dem perkutanen Klappenersatz ein neues Kapitel in der Therapie der kalzifizierten Aortenklappenstenose aufgeschlagen worden.

Today, tissue engineers are attempting to engineer virtually every human tissue. Potential tissue-engineered products include cartilage, bone, heart valves, nerves, muscle, bladder, liver, etc. Tissue engineering techniques generally require the use of a porous scaffold, which serves as a threedimensional template for initial cell attachment and subsequent tissue formation both in vitro and in vivo. The scaffold provides the necessary support for cells to attach, proliferate, and maintain their differentiated function. Its architecture de nes the ultimate shape of the new grown soft or hard tissue. In the early days of tissue engineering, clinically established materials such as collagen and polyglycolide were primarily considered as the material of choice for scaffolds. The challenge for more advanced scaffold systems is to arrange cells/ tissue in an appropriate 3D con guration and present molecular signals in an appropriate spatial and temporal fashion so that the individual cells will grow and form the desired tissue structures -and do so in a way that can be carried out reproducibly,economically, and on a large scale. This paper is not intended to provide a general review of tissue engineering, but speci cally concentrate on the design and processing of synthetic polymeric scaffolds. The material properties and design requirements are discussed. An overview of the various fabrication techniques of scaffolds is presented, beginning with the basic and conventional techniques to the more recent, novel methods that combine both scaffold design and fabrication capabilities.

Heart disease is a major cause of death in the Western world. In the past three decades there has been a number of improvements in artificial devices and surgical techniques for cardiovascular disease; however, there is still a need for novel devices, especially for those individuals who cannot receive conventional therapy. The major disadvantage of current artificial devices lies in the fact that they cannot grow, remodel, or repair in vivo. Tissue engineering offers the possibility of developing a biological substitute material in vitro with the inherent mechanical, chemical, biological, and morphological properties required in vivo, on an individual patient basis. In order to develop a true biological cardiovascular device a dynamic physiological environment needs to be created. One approach that employs the use of a simulated biological environment is a bioreactor in which the in vivo biomechanical and biochemical conditions are created in vitro for functional tissue development. A review of the current state of the art bioreactors for the generation of tissue engineered cardiovascular devices is presented in this study. The effect of the simulated physiological environment of the bioreactor on tissue development is examined with respect to the materials properties of vascular grafts, heart valves, and cardiac muscles developed in these bioreactors.

Introduction: This study describes the effect of introducing a cardiac sonographer led follow up clinic for patients with stable heart valve disease. The 2 years before and after the instigation of the valve clinic were audited. Materials and methods: The clinic was conducted in a single centre and undertaken in the cardiology department of a district general hospital. 382 patients, with 397 clinically significant valve lesions, but for whom surgery was not yet indicated but follow up required, were seen in a cardiac sonographer run clinics. These patients no longer attended a medical follow up clinic unless there was clinical or echocardiographic deterioration. Effectiveness was judged by the percentage treated according to current best practice guidelines, the number of echocardiograms performed and the number of hospital out patient visits attended. In addition mortality data for the subjects in the clinic was collected. Results: The proportion followed up according to best practice guidelines rose from 157 (41%) to 354 (92%) (p b 0.01). The total number of echocardiograms performed fell from 807 to 550. Total number of out patient visits fell from 998 to 31. 11 patients died in the two year study period, none from progressive valve disease. Discussion: This study demonstrates that a protocol driven sonographer led heart valve disease follow up clinic, significantly improved the quality of follow up while bringing about a major reduction in out patients visits, without compromising patient safety.

As a consequence of improved technology, there is growing clinical interest in the use of multi-detector row computed tomography (MDCT) for non-invasive coronary angiography. Indeed, the accuracy of MDCT to detect or exclude coronary artery stenoses has been high in many published studies. This report of a Writing Group deployed by the Working Group Nuclear Cardiology and Cardiac CT (WG 5) of the European Society of Cardiology and the European Council of Nuclear Cardiology summarizes the present state of cardiac CT technology, as well as the currently available data concerning its accuracy and applicability in certain clinical situations. Besides coronary CT angiography, the use of CT for the assessment of cardiac morphology and function, evaluation of perfusion and viability, and analysis of heart valves is discussed. In addition, recommendations for clinical applications of cardiac CT imaging are given and limitations of the technique are described.

Although current artificial heart valves are life sustaining medical devices, improvements are still necessary to address deficiencies. Bioprosthetic valves have a compromised fatigue life, while mechanical valves have better durability but are prone to thromboembolic complications.

Transplantation can be regarded as one form of "antiaging medicine" that is widely accepted as being effective in extending human life. The current number of organ transplants in the United States is on the order of 20,000 per year, but the need may be closer to 900,000 per year. Cadaveric and living-related donor sources are unlikely to be able to provide all of the transplants required, but the gap between supply and demand can be eliminated in principle by the field of regenerative medicine, including the present field of tissue engineering through which cell, tissue, and even organ replacements are being created in the laboratory. If so, it could allow over 30% of all deaths in the United States to be substantially postponed, raising the probability of living to the age of 80 by a factor of two and the odds of living to 90 by more than a factor of 10. This promise, however, depends on the ability to physically distribute the products of regenerative medicine to patients in need and to produce these products in a way that allows for adequate inventory control and quality assurance. For this purpose, the ability to cryogenically preserve (cryopreserve) cells, tissues, and even whole laboratory-produced organs may be indispensable. Until recently, the cryopreservation of organs has seemed a remote prospect to most observers, but developments over the past few years are rapidly changing the scientific basis for preserving even the most difficult and delicate organs for unlimited periods of time. Animal intestines and ovaries have been frozen, thawed, and shown to function after transplantation, but the preservation of vital organs will most likely require vitrification. With vitrification, all ice formation is prevented and the organ is preserved in the glassy state below the glass transition temperature (T G ). Vitrification has been successful for many tissues such as veins, arteries, cartilage, and heart valves, and success has even been claimed for whole ovaries. For vital organs, a significant recent milestone for vitrification has been the ability to routinely recover rabbit kidneys after cooling to a mean intrarenal temperature of about Ϫ45°C, as verified by life support function after transplantation. This temperature is not low enough for long-term banking, but research continues on preservation below Ϫ45°C, and some encouraging preliminary evidence has been obtained indicating that kidneys can support life after vitrification. Full development of tissue engineering and organ generation from stem cells, when combined with the ability to bank these laboratory-produced products, in theory could dramatically increase median life expectancy even in the absence of any improvements in mitigating aging processes on a fundamental level. 279

Bioprosthetic heart valves have evolved over the years into remarkably useful and predictable devices. During this process, a number of specific designs have come and gone, and a few have remained. Many design changes were successful, and many were not. This article will describe the successes and failures of the various bioprosthetic valve designs and will detail the specific reasons why a particular design change succeeded or failed to improve bioprosthetic valve performance.

Long Term Follow-up of the MAZE Pro- cedure for Treatment of Chronic Atrial Fibrilla- tion: Results after 3 Years. Background: The MAZE operation using microwave or radiofrequency to cre- ate atrial ablation lines is an established procedure in the treatment of chronic atrial fibrillation. This study investigates long term results after 36 months. Methods: Between 2/2001 and 12/2002 42 patients

The use of glutaraldehyde as a fixative in bioprostheses and drug delivery matrices is reviewed. The chemistry of glutaraldehyde cross-linking and its effect on the biological performance of a number of bioprostheses such as tissue heart valves, vascular grafts, pericardial patches, tendon grafts and drug delivery matrices are examined. Edwards supra-annular porcine bioprosthesis. Clinical experience and implantation characteristics. I Thorac Cardiovasc Surg 1986; 91: 555-565. Rupprath G, Thuer D, Vogt J et al. The durability of bioprostheses in young people. Long term results with intra-or extracardiac implanted porcine valves. J Cardiovasc Surg (Torino) 1985; 26: 251-257. Milan0 AD, Bortolotti U, Mazzucco A, Guerra F, Magna A, Gallucci V. Aortic valve replacement with Hancock standard, Bjork-Shiley and Lillehei-Kaster prostheses. A comparison based on follow-up from 1 to 15 years. J Thorac Cardiovasc Surg 1989; 98: 37-47. Kazui T, Morikawa M, Nakanishi K et al. Long-term results of mitral valve replacement using glutaraldehyde treated porcine bioprostheses-Comparison of the Hancock and Liotta valves. Jamieson WR, Munro AI, Miyagishima RT et al. The Carpentier-Edwards supra-annular porcine bioprosthesis: new generation low pressure glutaraldehyde fixed prosthesis. J Cardiac Surg 1988; 3: 507-521. Barratt-Boyes BG, Jaffe WM, Ko PH, Whitlock RM. The zero pressure Medtronic Intact porcine valve: an 8.5 year review. J Hearf Valve Dis 1993; 2: 604-611. Schoen FJ, Tsao JW, Levy RJ. Calcification of bovine pericardium used in cardiac valve bioprostheses. Implications for the mechanisms for bioprosthetic tissue mineralization. Am J Path01 1986; 123: 134-145. Moritz A, Grimm M, Eybl E et al. Improved spontaneous endothelialization by postfixation treatment of bovine pericardium. Em J Cardiothorac Surg 1991; 5: 155-159. Levy RJ, Schoen FJ, Levy JT, Nelson AC, Howard SL, Oshry LJ. Biologic determinants of dystrophic calcification and osteocalcin deposition in glutaraldehyde preserved porcine aortic valve leaflets implanted subcutaneously in rats. Am J Path01 1983; 113: 143-155. Golomb G, Schoen FJ, Smith MS, Linden J, Nixon M, Levy RJ. The role of glutaraldehyde-induced crosslinks in calcification of bovine pericardium used in cardiac valve bioprostheses. Am J Pathol 1987; 127: 122-130. Schoen FJ, Levy RJ. Calcification of bioprosthetic heart valves. In: Bodnar E, Frater RWM, eds. Replacemenf Cardiac Valves. Elmsford, NY: Pergamon Press, 1991: 125-148. Grimm M, Grabenwoger M, Eybl E et al. Improved biocompatibility of bioprosthetic heart valves by Lglutamic acid treatment.

Prosthetic heart valves epitomize both the triumphant advance of cardiac surgery in its early days and its stagnation into a retrospective, exclusive first world discipline of late. Fifty-two years after the first diseased heart valve was replaced in a patient, prostheses largely represent the concepts of the 1960s with many of their design-inherent complications. While the sophisticated medical systems of the developed world may be able to cope with sub-optimal replacements, these valves are poorly suited to the developing world (where the overwhelming majority of potential valve recipients reside), due to differences in age profiles and socio-economic circumstances. Therefore, it is the latter group which suffered most from the sluggish pace of developments. While it previously took less than 7 years for mechanical heart valves to develop from the first commercially available ball-in-cage valve to the tilting pyrolytic-carbon disc valve, and another 10 years to arrive at the all-carbon bi-leaflet design, only small incremental improvements have been achieved since 1977. Similarly, bioprosthetic valves saw their last major break-through development in the late 1960s when formalin fixation was replaced by glutaraldehyde cross linking. Since then, poorly understood so-called 'anti-calcification' treatments were added and the homograft concept rediscovered under the catch-phrase 'stentless'. Still, tissue valves continue to degenerate fast in younger patients, making them unsuitable for developing countries. Yet, catheter-delivered prostheses almost exclusively use bioprosthetic tissue, thereby reducing one of the most promising developments for patients of the developing world into a fringe product for the few first world recipients. With tissue-engineered valves aiming at the narrow niche of congenital malformations and synthetic flexible leaflet valves being in their fifth decade of low-key development, heart valve prostheses seem to be destined to remain an unsatisfying and exclusive first world solution for a long time to come. r

Theoretical models of the human heart valves are useful tools for understanding and characterizing the dynamics of healthy and diseased valves. Enabled by advances in numerical modeling and in a range of disciplines within experimental biomechanics, recent models of the heart valves have become increasingly comprehensive and accurate. In this paper, we first review the fundamentals of native heart valve physiology, composition and mechanics in health and disease. We will then furnish an overview of the development of theoretical and experimental methods in modeling heart valve biomechanics over the past three decades. Next, we will emphasize the necessity of using multiscale modeling approaches in order to provide a comprehensive description of heart valve biomechanics able to capture general heart valve behavior. Finally, we will offer an outlook for the future of valve multiscale modeling, the potential directions for further developments and the challenges involved.

A three-dimensional computational fluid dynamics (CFD) method has been developed to simulate the flow in a pumping left ventricle. The proposed method uses magnetic resonance imaging (MRI) technology to provide a patient specific, time dependent geometry of the ventricle to be simulated. Standard clinical imaging procedures were used in this study. A two-dimensional time-dependent orifice representation of the heart valves was used. The location and size of the valves is estimated based on additional long axis images through the valves. A semi-automatic grid generator was created to generate the calculation grid. Since the time resolution of the MR scans does not fit the requirements of the CFD calculations a third order bezier approximation scheme was developed to realize a smooth wall boundary and grid movement. The calculation was performed by a Navier–Stokes solver using the arbitrary Lagrange–Euler (ALE) formulation. Results show that during diastole, blood flow through the mitral valve forms an asymmetric jet, leading to an asymmetric development of the initial vortex ring. These flow features are in reasonable agreement with in vivo measurements but also show an extremely high sensitivity to the boundary conditions imposed at the inflow. Changes in the atrial representation severely alter the resulting flow field. These shortcomings will have to be addressed in further studies, possibly by inclusion of the real atrial geometry, and imply additional requirements for the clinical imaging processes.

Collagen is the main load bearing protein in many soft tissues, and in cardiovascular tissues in particular. In many tissues collagen has a specific architecture that is crucial for the biomechanical function of the tissue. Typical examples are the hammock-shaped collagen architecture in heart valves and a helical pattern in arteries. One of the objectives in cardiovascular tissue engineering is the reconstitution of this architecture. It is hypothesized that the architecture is mediated by mechanical stimulation. Computational models were developed to predict the mechanoregulation of the collagen architecture. This review recapitulates the key modeling assumptions and results achieved to date.

Biologically active heart valves (tissue engineered and recellularized tissue-derived heart valves) have the potential to offer enhanced function when compared to current replacement value therapies since they can possibly remodel, and grow to meet the needs of the patient, and not require chronic medication. However, this technology is still in its infancy and many fundamental questions remain as to how these valves will function in vivo. It has been shown that exposing biologically active tissue constructs to pulsatile pressures and flows during in vitro culture produces enhanced extracellular matrix protein expression and cellularity, although the ideal hydrodynamic conditioning regime is as yet unknown. Moreover, in vitro organ-level studies of living heart valves aimed at studying the remodeling processes require environments that can accurately reproduce in vivo hemodynamics under sterile conditions. To this end, we have developed a system to study the effects of subjecting biologically active heart valves to highly controlled pulsatile pressure and flow waveforms under sterile conditions. The device fits inside a standard incubator and utilizes a computer-controlled closed loop feedback system to provide a high degree of control. The mean pressure, mean flow rate, driving frequency, and shape of the pulsatile pressure waveform can be changed automatically in order to simulate both physiologic and nonphysiologic hemodynamic conditions. Extensive testing and evaluation demonstrated the device's ability to subject a biologically active heart valve to highly controlled pulsatile waveforms that can be modulated during the course of sterile incubation.

Background. Uncertainty about long-term effects of surgically unaddressed moderate (2؉) secondary tricuspid valve (TV) regurgitation (TR) accompanying leftsided degenerative heart valve disease led us to identify reasons for and factors associated with TV repair, compare safety and clinical effectiveness of relieving TR, and identify factors associated with severe (3/4؉) postoperative TR.

Background: Zero-dimensional (lumped parameter) and one dimensional models, based on simplified representations of the components of the cardiovascular system, can contribute strongly to our understanding of circulatory physiology. Zero-D models provide a concise way to evaluate the haemodynamic interactions among the cardiovascular organs, whilst one-D (distributed parameter) models add the facility to represent efficiently the effects of pulse wave transmission in the arterial network at greatly reduced computational expense compared to higher dimensional computational fluid dynamics studies. There is extensive literature on both types of models. Method and Results: The purpose of this review article is to summarise published 0D and 1D models of the cardiovascular system, to explore their limitations and range of application, and to provide an indication of the physiological phenomena that can be included in these representations. The review on 0D models collects together in one place a description of the range of models that have been used to describe the various characteristics of cardiovascular response, together with the factors that influence it. Such models generally feature the major components of the system, such as the heart, the heart valves and the vasculature. The models are categorised in terms of the features of the system that they are able to represent, their complexity and range of application: representations of effects including pressure-dependent vessel properties, interaction between the heart chambers, neuro-regulation and auto-regulation are explored. The examination on 1D models covers various methods for the assembly, discretisation and solution of the governing equations, in conjunction with a report of the definition and treatment of boundary conditions. Increasingly, 0D and 1D models are used in multi-scale models, in which their primary role is to provide boundary conditions for sophisticate, and often patient-specific, 2D and 3D models, and this application is also addressed. As an example of 0D cardiovascular modelling, a small selection of simple models have been represented in the CellML mark-up language and uploaded to the CellML model repository http://models.cellml.org/. They are freely available to the research and education communities. Conclusion: Each published cardiovascular model has merit for particular applications. This review categorises 0D and 1D models, highlights their advantages and disadvantages, and thus provides guidance on the selection of models to assist various cardiovascular modelling studies. It also identifies directions for further development, as well as current challenges in the wider use of these models including service to represent boundary conditions for local 3D models and translation to clinical application. Shi et al. BioMedical Engineering OnLine 2011, 10:33

In this paper, a decision support system that classifies the Doppler signals of the heart valve to two classes (normal and abnormal) is presented to support the cardiologist. The paper uses our previous paper where ANN is used as a classifier, as feature extractor from measured Doppler signal. To make this, it uses wavelet transforms and short time Fourier transform methods. Before it classifies these features, it applies Wavelet entropy to them. In this paper, our aim is to develop our previous work by using least-squares support vector machine (LS-SVM) classifier instead of ANN. We use LS-SVM and backpropagation artificial neural network (BP-ANN) to classify the extracted features. In addition, we use receiver operator characteristic (ROC) curves to compare sensitivities and specificities of these classifiers and compute the area under the curves. Finally, we evaluate two classifiers in all aspects. ᭧

Objective: Pulmonary valve replacement is performed increasingly late after correction of Tetralogy of Fallot. Most reports deal with pulmonary allografts as the valvar substitute of choice, although late deterioration and reoperation(s) are the rule. Mechanical valves are scarcely reported and if so only because of complications. Although life-long anticoagulation therapy is indicated for mechanical prostheses, the chance of subsequent re-operations can be expected to be low. We report the results of 28 mechanical valve replacements in the pulmonary position. Methods: A mechanical valve was implanted in 27 of 79 patients indicated for pulmonary valve replacement. Tetralogy of Fallot was the most common basic lesion. The results and follow-up were reviewed retrospectively, where death and re-operation were primary end points. Routine outpatient follow-up, including trans-thoracic echocardiography, was performed. Results: Twenty-eight pulmonary valve implantations were done in 27 patients. Thirty-day hospital mortality was 1/28 (3.6%), because of a cerebro-vascular accident. One patient died late (2.8 years postoperatively). Median age was 33 years and the median interval between primary repair and insertion of the prosthesis was 26 years. Freedom from re-operation at 1 year was 100%. One valve had to be replaced 14 years after implantation because of malfunction due to ingrowth of endomyocardial fibrosis. No thrombo-embolic events were observed. Conclusions: Our series do not confirm the bad reputation of mechanical valvar prostheses in the pulmonary position. On the contrary they perform well and result in a much lower re-operation rate than can be expected and in fact is reported after allograft usage. No thrombo-embolic complications were noted. In our experience pulmonary mechanical valve prostheses do well. #

Poly(Styrene-block-IsoButylene-block-Styrene) (''SIBS'') is a biostable thermoplastic elastomer with physical properties that overlap silicone rubber and polyurethane. Initial data collected with SIBS stent-grafts and coatings on metallic stents demonstrate hemocompatibility, biocompatibility and long-term stability in contact with metal. SIBS has been used successfully as the carrier for a drug-eluting coronary stent; specifically Boston Scientific's TAXUS s stent, and its uses are being investigated for ophthalmic implants to treat glaucoma, synthetic heart valves to possibly replace tissue valves and other applications. At present, researchers developing medical devices utilizing SIBS have found the following: (1) SIBS does not substantially activate platelets in the vascular system; (2) polymorphonuclear leukocytes in large numbers are not commonly observed around SIBS implants in the vascular system or in subcutaneous implants or in the eye; (3) myofibroblasts, scarring and encapsulation are not clinically significant with SIBS implanted in the eye; (4) embrittlement has not been observed in any implant location; (5) calcification within the polymer has not been observed; and (6) degradation has not been observed in any living system to date. Some deficiencies of SIBS that need to be addressed include creep deformation in certain load-bearing applications and certain sterilization requirements. The reason for the excellent biocompatibility of SIBS may be due to the inertness of SIBS and lack of cleavable moieties that could be chemotactic towards phagocytes. r

Detergents are powerful agents for tissue decellularization. Despite this, the high toxicity of detergent residua can be a major limitation. This study evaluated the efficacy of detergent removal from decellularized pulmonary valves (PVs) and the consequences of repopulation with human endothelial cells (HECs). Porcine PVs were treated with 1% sodium deoxycholate (SDC), group A; 1% sodium dodecyl sulfate (SDS), group B; and a mixture of 0.5% SDC/0.5% SDS, group C (n = 5 each). After each of 10 succeeding wash cycles (WCs), samples of the washing solution (WS) were analyzed by solid phase extraction and high performance liquid chromatography for the presence of detergents. Metabolic activity of HEC was also assessed in the WS samples (cytotoxicity and MTS assays). Decellularized and washed PVs were reseeded with HEC. Histological analysis demonstrated efficient tissue decellularization in all groups. Detergents' concentration in all WSs decreased exponentially and was below 50 mg/L after 6, 8, and 4 WCs in groups A, B, and C, respectively. This concentration resulted in no significant toxic influence on cell cultures, and scaffolds could be efficiently reseeded with HEC. In conclusion, intensive washing of detergent decellularized valvular scaffolds lowers the residual contamination below a hazardous threshold and allows their successful repopulation with HEC for tissue engineering purposes.

Poly(Styrene-block-IsoButylene-block-Styrene) (''SIBS'') is a biostable thermoplastic elastomer with physical properties that overlap silicone rubber and polyurethane. Initial data collected with SIBS stent-grafts and coatings on metallic stents demonstrate hemocompatibility, biocompatibility and long-term stability in contact with metal. SIBS has been used successfully as the carrier for a drug-eluting coronary stent; specifically Boston Scientific's TAXUS s stent, and its uses are being investigated for ophthalmic implants to treat glaucoma, synthetic heart valves to possibly replace tissue valves and other applications. At present, researchers developing medical devices utilizing SIBS have found the following: (1) SIBS does not substantially activate platelets in the vascular system; (2) polymorphonuclear leukocytes in large numbers are not commonly observed around SIBS implants in the vascular system or in subcutaneous implants or in the eye; (3) myofibroblasts, scarring and encapsulation are not clinically significant with SIBS implanted in the eye; (4) embrittlement has not been observed in any implant location; (5) calcification within the polymer has not been observed; and (6) degradation has not been observed in any living system to date. Some deficiencies of SIBS that need to be addressed include creep deformation in certain load-bearing applications and certain sterilization requirements. The reason for the excellent biocompatibility of SIBS may be due to the inertness of SIBS and lack of cleavable moieties that could be chemotactic towards phagocytes. r

Assessment of normal and abnormal function of heart valve prostheses remains challenging. Doppler echocardiography has been shown to allow hemodynamic evaluation in various clinical settings and has become the most widely used tool to assess prosthetic valve function. Prosthetic valves, even when they function normally, are to some degree obstructive to the blood flow. The normal values of gradients, pressure half-time, and effective orifice area depend on valve type and valve size. Doppler assessment of prosthetic valve function, thus, requires specification of valve type and valve size, and knowledge of the normal values.

Currently, many medical devices are made of implantable metals such as 316LVM stainless steel. Electropolishing is a common process to obtain a smooth surface, free of contaminants and more passive, which allows for minimizing the foreign body response and cell adhesion. However, polishing of small implants with a highly complicated geometry and nonuniform metallurgy might result in unsatisfactory results. The objective of this work was to develop an electropolishing process effective for complex metallic implants such as artificial heart valve frames and miniature glaucoma implants. Polishing in an ultrasonic bath and pulsed voltage polishing processes were studied and compared to the standard ASTM process. Currentvoltage curves were constructed for different solutions and bath temperatures. The polished parts were evaluated by stereomicroscopy, optical microscopy, atomic force microscopy, noncontact surface profilometry, and X-ray diffraction. Pulse polishing was found useful in eliminating the erosion effects of gas bubbles in solution. Electropolishing in an ultrasonic bath was found useful when a rough, patterned surface is needed, e.g. for osseointegration purposes. Preliminary animal studies followed by histopathology indicated that the polished surfaces stimulated only a moderate body reaction, as desired in such applications. The pronounced dependence of the measured roughness values on both the measurement technique and scanned area should inspire the preparation of a new testmethod standard.

We report a case of redo aortic prosthesis replacement for a severe paravalvular leak (PVL) in a man operated with continuous suture technique 7 years earlier. The severe aortic regurgitation was due to the rupture of the suture. In spite of operations to replace malfunctioning heart valves are common procedures and performed all over the world from more than 50 years, there is still an open debate about the most suitable suture technique. In this case report, we'll discuss if the suture technique has a role in preventing or leading complications as severe PVL.

Biocompatibility assays indicated that human blood vessel cells survive and proliferate on matrix/polymer hybrid tissue. In vitro activation of cellular and plasmatic coagulation cascades was lower than with uncoated control tissue. After implantation in the rabbit aorta, matrix/ ...

Mitral valve surgery can be performed through the trans-atrial or the trans-septal approach. Although the trans-atrial is the preferred method, the trans-septal approach has also been used recently and has a particular value in beating-heart mitral valve surgery. Herein we report our experience with beating-heart mitral valve surgery via trans-septal approach, and discuss its advantages and pitfalls. Between 2000 and 2007, 214 consecutive patients were operated upon utilizing beating heart technique for mitral valve surgery. The operation was performed via transseptal approach with the aorta unclamped, the heart beating, with normal electrocardiogram and in sinus rhythm. Mean age was 56.03 +/- 13.93 years (range: 19-86 years; median: 56 years). There were 131 (61.2%) males and 83 (38.8%) females. Of the prostheses used, 108 (50.5%) were biological, and 39 (18.2%) were mechanical. Mitral repairs were performed in 67 (31.3%) patients. Mean hospital stay was 17.4 +/- 20.0 days (range: ...

By January 1994, a total of 40 Wessex porcine bioprostheses (21 mitral, 18 aortic, and 1 tricuspid) were explanted from 31 subjects. They belonged to a series of 150 patients who received 184 of such prostheses in our unit. Seventeen of these explanted prostheses were available for study, and 11 of them presented some sort of stent fracture or fissuring (mean of 3.6 * 1.6 fractures per prosthesis). The disruption occurred in all cases at the base of the commissural arch or at the commissural bar of the stent. The fractures were not detected clinically nor echocardiographically before reoperation, and most valves were explanted for reasons other than the stent rupture itself. The actuarial probability of freedom from stent fracture in our series is 66 12% at 9 years of follow-up. In our experience, fracture of the stent is an important mode of structural dysfunction of the Wessex porcine bioprostheses.

Heart valve allografts (usually referred to as 'homografts') have been used in cardiac surgery for over 45 years when they were amongst the first valves ever used. Today they remain an important part of valve replacement and reconstructive surgery, particularly in the field of congenital heart disease. There are currently seven tissue banks on the UK and Eire that procure, prepare and store these homografts for surgical implantation, currently providing around 700 grafts per year. This article reviews the history and applications of homografts and compares their performance and outcomes with current prosthetic alternatives. It also describes the processes of valve procurement and storage and describes their clinical applications, hopefully providing tissue bankers with the surgeon's insight into what is required. Homograft degeneration and the natural history of these tissues is discussed, together with future expectations and developments in homograft valve technology.