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At least 505 records · Page 28Linked to original sources
PubMed1996

Cavitation dynamics of medtronic hall mechanical heart valve prosthesis: fluid squeezing effect.

The cause of cavitation in mechanical heart valves is investigated with Medtronic Hall tilting disk valves in an in vitro flow system simulating the closing event in the mitral position. Recordings of pressure wave forms and photographs in the vicinity of the inflow surface of the valve are attempted under controlled transvalvular loading rates averaged during valve closing period. The results revealed presence of a local flow field with a very high velocity around the seat stop of mechanical heart valves that could induce pressure reduction below liquid vapor pressure and a cloud of cavitation bubbles. The analysis of the results indicates that the "fluid squeezing" between the stop and occluder as the main cause of cavitation in Medtronic Hall valves. The threshold loading rate for cavitation initiation around the stop was found to be very low (300 and 400 mmHg/s; half the predicted normal human loading rate that was estimated to be 750 mmHg/s) because even a mild impact created a high speed local flow field on the occluder surface that could induce pressure reduction below vapor pressure. The present study suggests that mechanical heart valves with stops at the edge of major orifice region are more vulnerable to cavitation, and hence, have higher potential for damage on valve components and formed elements in blood.

Blood Flow Velocity↗
PubMed2005

Numerical simulation of cardiovascular dynamics with healthy and diseased heart valves.

This paper presents a new concentrated parameter model for cardiovascular dynamics that includes an innovative model of heart valve dynamics, which is embedded in the overall model of the four chambers of the heart and the systemic and pulmonary circulation loops. The heart chambers are described with a variable elastance model, and the systemic and pulmonary loops are described with modified Windkessel models. In modelling the heart valve dynamics, the various factors that influence the valve motion are examined, and the governing differential equation for valve motion is derived. The heart valve model includes the influence of the blood pressure effect, the friction effect from the tissue, and from blood motion. As improvement from previous works, the contribution of the blood vortex effect in the vicinity of the valve leaflets to valve motion is specially considered. The proposed model is then used in simulation of healthy and certain pathological conditions such as mitral valve stenosis and aortic regurgitation. The predicted results agree well with results illustrated in cardiology textbooks.

Adult↗
PubMed2001

In-vitro measurements of the regurgitation of mechanical mitral heart valve prostheses in case of atrial fibrillation.

BACKGROUND AND AIM OF THE STUDY: The characterization of heart valve prostheses requires regurgitation tests to be conducted in pulsatile flow. Although tests are generally conducted in accordance with hemodynamic conditions of a healthy young man, heart valve implantation is often associated with other pathology, such as atrial fibrillation. To run more realistic trials, four mechanical heart valve prostheses were tested with, and then without, atrial contraction. METHODS: The dual activation simulator (DAS) allow simulation of physiologically normal and pathological flows through the mitral valve. The DAS comprises silicon-based cavities, is activated by pumps, and was equipped successively with monoleaflet (Björk-Shiley, Medtronic Hall) and bileaflet (St. Jude Medical, CarboMedics) valves. Each valve (mitral, size 27 mm) was tested under two conditions (with and without atrial contraction) at a mean flow rate of 3 l/min of glycerol/water solution (analog blood viscosity). RESULTS: Leakage volumes were of the same magnitude as the precision of the instruments. Respectively, closing volumes increased from normal conditions to atrial fibrillation from 3.2 to 5.1 ml for Björk-Shiley, from 4.6 to 6.3 ml for Medtronic Hall, from 5 to 6.6 ml for St. Jude Medical, and from 5.2 to 5.4 ml for CarboMedics. The standard deviation was below the precision of measurements (+/- 0.5 ml). CONCLUSION: Without atrial contraction, the valves seemed to be closed by backward flow only, thus confirming earlier reports. This study showed that different heart valves behave differently in pathological situations with regard to their design; this must be considered when selecting a valve for implantation.

Atrial Fibrillation↗
PubMed1998

Clinical evaluation and analysis of heart valve substitutes.

We discuss the clinical assessment of heart valve substitutes, primarily with regard to pre-market evaluation. We concentrate on the current FDA heart valve guidance document. This guidance is self-acknowledged to be an evolving document, scheduled to be revised between three and five years after its initial release on December 1993. We outline the history and some of the strengths of the present system, and discuss areas for possible improvement. We selected one important statistical issue to address thoroughly how to compute the confidence limit of a linearized rate.

Bioprosthesis↗
PubMed2001

Obstruction of mechanical heart valve--diagnosis, surgical treatment and outcome.

From 1982 till 1999, our department performed a total of 2970 heart valve replacements--92% of which were with mechanical heart valves. During this period, there were 8 patients who came to our department with mechanical heart valve obstruction. All these patients presented with signs of heart failure or compromised haemodynamic. Confirmatory tests included transthoracic or transoesophageal echocardiography and cine fluoroscopy. Seven patients were operated upon urgently. Four of the patients had valve thrombosis. The time interval between the initial implantation and presentation varies from 4 months to 11.3 years. Six of the seven patients who were operated on recovered well from the surgery.

Adolescent↗
PubMed1996

In vitro endothelialization of bioprosthetic heart valves.

BACKGROUND AND AIMS OF THE STUDY: The main disadvantage of xenograft bioprosthetic heart valves is limited durability due to tissue degeneration. METHODS: To study possible alternatives to conventional bioprosthetic heart valves, glutaraldehyde preserved porcine aortic valve leaflets were precoated with fibronectin-heparin and acidic fibroblast growth factor (aFGF) to enhance cell proliferation. Furthermore, different methods of storage and preservation (1.0% benzoic acid, 1.0% sorbic acid, 0.05% and 0.5% dialdehyde starch) were compared to conventional preservation procedures. Valve leaflets were lined with adult human saphenous vein endothelial cells (1.0 x 10(4) AHSVEC/cm2). The different methods of preservation were compared to leaflets precoated additionally with 1.0 microgram/cm2 aFGF protein, derived from gene manipulated bacteria. Endothelial growth kinetics were studied and verified by an increase of activation following 3H-thymidine incorporation, while the maintained metabolic cell activity was demonstrated by prostacyclin (PGI2) release measurements. In subsequent experiments in vivo degeneration and mineralization were determined by subcutaneous implantation in rats for up to 40 days. RESULTS: Our results favored alternatively treated valve leaflets; endothelial cells grew to persistent monolayers in six to 12 days in contrast to conventional processed leaflets where no endothelial cell growth was possible. Atomic absorption spectroscopic assessment of subdermal valve implants showed significantly lower contents of calcium, magnesium and phosphate in alternatively treated leaflets. Furthermore, precoating of alternatively preserved valve leaflets with aFGF protein and endothelial cells improved in vitro and in vivo results significantly. CONCLUSIONS: Our study shows that endothelial cell growth as well as significantly reduced in vivo degeneration and mineralization of valve leaflets may be feasible if bioprosthetic heart valves are processed according to alternative, non-toxic conservation procedures and are precoated with angiogenic growth factor protein.

Adult↗
PubMed1997

Increased cellular expression of matrix proteins that regulate mineralization is associated with calcification of native human and porcine xenograft bioprosthetic heart valves.

Dystrophic mineralization remains the leading cause of stenotic or regurgitant failure in native human and porcine bioprosthetic heart valves. We hypothesized that cellular expression of noncollagenous matrix proteins (osteopontin, osteocalcin, and osteonectin) that regulate skeletal mineralization may orchestrate valvular calcification. Porcine bioprosthetic heart valves and native human heart valves obtained during replacement surgery were analyzed for cells, matrix proteins that regulate mineralization, and vessels. Cell accumulation and calcification were correlated for both valve types (rho = 0.75, P = 0.01, native; rho = 0.42, P = 0.08, bioprosthetic). Osteopontin expression correlated with cell accumulation (rho = 0.58, P = 0.04) and calcification (rho = 0.52, P = 0.06) for bioprosthetic valves. Osteocalcin expression correlated with calcification (rho = 0.77, P = 0.04) and cell accumulation (rho = 0.69, P = 0.07) in native valves. Comparisons of calcified versus noncalcified native and bioprosthetic valves for averaged total matrix protein mRNA signal score revealed increased noncollagenous proteins mRNA levels in calcified valves (P = 0.07, group I vs. group II; P = 0.02, group III vs. group IV). When stratified according to positive versus negative mRNA signal status, both calcified bioprosthetic valves (P = 0.03) and calcified native valves (P = 0.01) were significantly more positive for noncollagenous proteins mRNA than their noncalcified counterparts. Local cell-associated expression of proteins regulating mineralization suggests a highly coordinated mechanism of bioprosthetic and native valve calcification analogous to physiologic bone mineralization. Modulation of cellular infiltration or cellular expression of matrix proteins that regulate mineralization, may offer an effective therapeutic approach to the prevention of valve failure secondary to calcification.

Aged↗
PubMed2006

Decellularized heart valve as a scaffold for in vivo recellularization: deleterious effects of granulocyte colony-stimulating factor.

BACKGROUND: Autologous recellularization of decellularized heart valve scaffolds is a promising challenge in the field of tissue-engineered heart valves and could be boosted by bone marrow progenitor cell mobilization. The aim of this study was to examine the spontaneous in vivo recolonization potential of xenogeneic decellularized heart valves in a lamb model and the effects of granulocyte colony-stimulating factor mobilization of bone marrow cells on this process. METHODS: Decellularized porcine aortic valves were implanted in 12 lambs. Six lambs received granulocyte colony-stimulating factor (10 microg x kg(-1) x d(-1) for 7 days, granulocyte colony-stimulating factor group), and 6 received no granulocyte colony-stimulating factor (control group). Additionally, nondecellularized porcine valves were implanted in 5 lambs (xenograft group). Angiographic and histologic evaluation was performed at 3, 6, 8, and 16 weeks. RESULTS: Few macroscopic modifications of leaflets and the aortic wall were observed in the control group, whereas progressive shrinkage and thickening of the leaflets appeared in the granulocyte colony-stimulating factor and xenograft groups. In the 3 groups progressive ovine cell infiltration (fluorescence in situ hybridization) was observed in the leaflets and in the adventitia and the intima of the aortic wall but not in the media. Neointimal proliferation of alpha-actin-positive cells, inflammatory infiltration, adventitial neovascularization, and calcifications were more important in the xenograft and the granulocyte colony-stimulating factor groups than in the control group. Continuous re-endothelialization appeared only in the control group. CONCLUSION: Decellularized xenogeneic heart valve scaffolds allowed partial autologous recellularization. Granulocyte colony-stimulating factor led to accelerated heart valve deterioration similar to that observed in nondecellularized xenogeneic cardiac bioprostheses.

Actins↗
PubMed1987

[Diagnosis and outcome of dysfunction of mechanical prostheses of the heart valves (analysis of 143 cases)].

Diagnosis of dysfunction of heart valve prostheses has been reviewed in 143 patients over 17 years of follow-up. Sixty-eight paravalvular fistulas, 69 thromboses and 6 prosthetic ball or disk changes have been detected. Sepsis was the cause of prosthetic dysfunction in 61 (42.7%) patients. Diagnosis was difficult to make in cases of thrombosis in the area of the ventricular ring of the mitral prosthesis, thrombosis of the aortic prosthesis and ball changes. Because of similar phonocardiographic features, thrombosis of the obturative part of mitral prosthesis should be differentiated from thrombosis of the atrial part of the prosthesis and paravalvular fistula. The absence of diastolic murmur and prevailing symptoms of right ventricular insufficiency are distinctive features of obturator thrombosis rather than atrial thrombosis of the prosthesis. Thrombosis of the aortic prosthesis or a ball change should be suspected, if the ratio of the opening to closing tone amplitude drops below 0.5 and intermittent protodiastolic murmur emerges. Clinical phonocardiographic studies are capable of detecting prosthetic dysfunction in most cases.

Aortic Valve↗
PubMed1990

[Problems of surgical treatment of dysfunction of heart valve prosthesis].

The article generalizes experience in surgical treatment of disturbed functioning of heart valve prostheses. Functioning was impaired in 3.2% of 5113 prostheses. Operations were repeated in disturbed functioning of heart valve prostheses in 58 (35.4%) patients, in 7 of them the intervention was repeated twice. Closure of fistulas (26.2%) is possible only in moderate paravalvular+ insufficiency which is not connected with septic endocarditis. The authors emphasize the great risk of repeated operations, which calls for special attention to be paid to the prevention of disturbed functioning of heart valve prostheses.

Aortic Valve Insufficiency↗
PubMed2002

[Is chronic graft rejection the reason for degenerative changes in allogeneic and xenogeneic heart valve prostheses: immunohistochemical evaluation of inflammatory factors].

OBJECTIVES: After a period of 5 to 10 years, biological heart valve prostheses undergo degenerative processes, which finally lead to dysfunction and complete destruction. Although many efforts have been made to identify underlying mechanisms, many questions remain unanswered. Here we evaluate immunological factors and their potential role in biological heart valve destruction. PATIENTS AND METHODS: Allogeneic (n=10) and xenogeneic (n=3) aortic valvular prostheses, as well as aortic valves retrieved from transplanted human hearts, which had to be replaced because of chronic graft rejection (n=4) were analyzed. Aortic valves from human donor hearts (native) (n=4), which were considered not transplantable served as controls. Endothelial expression patterns of the following adhesion molecules were analyzed by immunohistochemistry: selectin family: ELAM-1, CD62, integrin family: VLA-1, -2, -3, -4, -5, and -6, immunoglobulin supergene family: PECAM-1, ICAM-1, and -2, and class I heavy chain proteins, complementary adhesion molecules: CD34, CD44 and the von Willebrand factor. RESULTS: ELAM-1, ICAM-1 and -2, CD34, CD44 and class I heavy chain proteins, all molecules which play significant roles during inflammatory processes, showed stronger expression patterns in allogeneic and xenogeneic aortic heart valve prostheses compared to native or chronically rejected valves. Furthermore, the von Willebrand factor stained positive only on allogeneic and xenogeneic valves. Only mild differences were observed regarding the expression of integrin molecules and CD62. CONCLUSIONS: Immunological reactions play a major role in the degeneration of biological heart valve prostheses. This is underlined by observations made on aortic valves from chronically rejected cardiac grafts, which did not show any degenerative alterations. Thus, since immunosuppressive therapy after heart valve replacement is no reasonable alternative, novel and future approaches in "tissue engineering" will hopefully help avoid tissue degeneration, while preserving the advantage of biological tissue origin.

Animals↗
PubMed1987

Pericardial heterograft valves: an assessment of leaflet stresses and their implications for heart valve design.

Bovine pericardium, stabilized with glutaraldehyde, is used widely in the construction of heart valve substitutes, but the design and construction of valve substitutes from this material are empirically based. Collagenous tissue can support tension, but experimental evidence indicates that flexure-induced compressive stresses can lead to fatigue failure. This study uses experimental results obtained from cyclic uniaxial load tests to predict the type and magnitude of operational stresses which occur in pericardial heterograft leaflets. Both Young's modulus and Poisson's ratio varied with uniaxial loading in pericardium, chemically modified free of tension. Leaflet stresses were analysed in using effective incremental representations of these parameters. In leaflets with unrestricted rotation at the point of attachment to the stent, the mid-plane tensions always exceeded the bending stresses, and no zones of leaflet compression were predicted. In contrast, with totally restricted leaflet rotation induced by clamping (possibly between a male and female frame) the bending stresses were greater than the mid-plane tensions at the hinge line and significant compressive stresses were predicted at this site. If elastic boundary conditions were introduced at the stent (possibly by wrapping the stent in pericardium) then the compressive stresses were reduced as the degree of elasticity was increased. Glutaraldehyde fixation of the pericardium under load produced a stiffer material; higher compressive stresses at the stent and significant increases in total stress were predicted for this tissue. The application of elevated pressure loading also increased the compressive and total stresses in the leaflet. Finally, it was shown that bicuspid leaflets were likely to experience higher stresses than tricuspid leaflets. This simple stress analysis should help valve designers of pericardial heterografts to identify those conditions which lead to tissue compression, high total stress, and ultimately material fatigue.

Animals↗
PubMed2003

[Anticoagulation in pregnant women with prosthetic heart valve--a new approach for therapy].

The treatment of women in childbearing age with a mechanical heart valve is a challenge for the medical staff. Warfarin (Coumadin) is considered to be a safe and effective anticoagulant for patients with prosthetic heart valves. However, treatment during pregnancy poses many difficulties, especially during the first trimester, due to its ability to cross the placenta and its associated fetotoxicity. Treatment with heparin during the first trimester decreases the rate of embryopathy, but increases maternal morbidity and mortality. Warfarin therapy throughout pregnancy, which is common mainly in Europe, carries low rates of maternal complications and roughly six percent of embryopathy. Several studies compared warfarin treatment throughout pregnancy versus treatment with heparin during the first trimester. The relationship between daily warfarin doses and the rate of embryopathy was recently investigated. We report two cases of pregnant women with mechanical heart valves who were treated with heparin during the first trimester. Both underwent an emergency replacement of the prosthetic valve during the eighth week of pregnancy. In this article, we review the literature regarding anticoagulation therapy in pregnant women with prosthetic heart valves; the comparison between treatment with warfarin throughout pregnancy and heparin in the first trimester; and the relation of daily warfarin doses with the rate of embryopathy. The two case reports demonstrate the common approach for therapy and the danger within it. In the discussion we present a new approach for treating pregnant women with prosthetic valve and guidelines for the medical staff.

Adult↗
PubMed1996

A microstructural flow analysis within a bileaflet mechanical heart valve hinge.

BACKGROUND AND AIMS OF THE STUDY: During recent clinical trials, the Medtronic Parallel bileaflet heart valve was found to have an unacceptable thrombosis complication rate. As patient- and material-related factors proved negative causes for this outcome, it was hypothesized that the flow fields within the valve's hinge pocket contributed to the thrombus formation. METHODS: A microstructural flow analysis within the hinge pocket is presented which uses the techniques of flow visualization, computational fluid dynamics (CFD), and laser Doppler velocimetry (LDV). The application of these techniques towards solving this problem has become possible through (i) the ability to manufacture dimensionally correct 1-X transparent heart valve housings, (ii) advances in CFD technology, and (iii) advances in LDV measurement techniques. RESULTS: This analysis showed that a vortex was present at the hinge pocket's inflow channel during forward flow and degenerated to a disturbed three-dimensional structure during reverse flow with zones of turbulent shear stress large enough to cause blood cell damage. In addition, multiple zones of flow stagnation and disturbed flow existed along the leaflet's pivot throughout the entire cardiac cycle. It was felt that these complex fluid structures created conditions which resulted in the formation of thrombus within the hinges of the Medtronic Parallel valve. These findings were supported by limited clinical explant data which illustrated early thrombus formation within the Parallel valve's hinge pocket at sites predicted by the analysis. CONCLUSIONS: This study provides, for the first time, an understanding of the detailed flow structures within the hinges of a mechanical heart valve and demonstrates an analysis technique by which future mechanical heart valve designs may be assessed for the potential of thrombus formation within the valve's hinge regions.

Computer Simulation↗
PubMed1993

Cinefluoroscopic identification of Björk-Shiley prosthetic heart valves.

Numerous mechanical prostheses are currently utilized for heart valve replacement. Fluoroscopy is a useful technique to identify prosthetic valves, to evaluate their function and to follow-up the patients' condition. Scattered and contrasting data, however, have been reported about the radiographic appearance of Björk-Shiley heart valves. This study shows that each Björk-Shiley valve model has characteristic radiographic features that can be readily determined by fluoroscopic evaluation, leading to easy and accurate non-invasive identification.

Fluoroscopy↗