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PubMed2006

Fluid dynamic assessment of three polymeric heart valves using particle image velocimetry.

Polymeric heart valves have the potential to reduce thrombogenic complications associated with current mechanical valves and overcome fatigue-related problems experienced by bioprosthetic valves. In this paper we characterize the in vitro velocity and Reynolds Shear Stress (RSS) fields inside and downstream of three different prototype trileaflet polymeric heart valves. The fluid dynamic differences are then correlated with variations in valve design parameters. The three valves differ in leaflet thickness, ranging from 80 to 120 mum, and commisural design, either closed, opened, or semi-opened. The valves were subjected to aortic flow conditions and the velocity measured using three-dimensional stereo Particle Image Velocimetry. The peak forward flow phase in the three valves was characterized by a strong central orifice jet of approximately 2 m/s with a flat profile along the trailing edge of the leaflets. Leakage jets, with principle RSS magnitudes exceeding 4,500 dyn/cm(2), were observed in all valves with larger leaflet thicknesses and also corresponded to larger leakage volumes. Additional leakage jets were observed at the commissural region of valves with the open and the semi-open commissural designs. The results of the present study indicate that commissural design and leaflet thickness influence valve fluid dynamics and thus the thrombogenic potential of trileaflet polymeric valves.

Blood Flow Velocity↗
PubMed1988

Incidence of primary tissue valve failure in porcine bioprosthetic heart valves.

This report provides retrospective follow-up data on 324 consecutive patients who received a Hancock-I porcine valve in the aortic or the mitral position, or in both positions, between June, 1974, and December, 1976. This analysis included 319 valves (193 mitral, 126 aortic) available for study of the incidence of primary tissue valve failure after 10 to 12.5 years of follow-up. Of the 319 prostheses at risk, 114 instances of primary tissue valve failure occurred. Seventy-three of the failed valves were in the mitral position, and 41 were in the aortic position. The calculated actuarial probability of freedom from primary tissue valve failure was 52 +/- 5% for the mitral and 58 +/- 6% for the aortic prostheses at 12.5 years of follow-up. For patients older than 40 years at the time of operation, the rate of freedom from primary failure was 68 +/- 8% and 55 +/- 6% for aortic and mitral prostheses, respectively, at 12.5 years. Comparison of both actuarial curves disclosed no meaningful difference. However, a tendency toward greater failure rate was observed in the mitral prosthesis group.

Adolescent↗
PubMed2005

Design and in vitro performance of a novel bileaflet mechanical heart valve prosthesis.

Design and in vitro performance of a novel bileaflet mechanical heart valve prosthesis are presented. The novel heart valve exhibits three main design characteristics: (i) The leaflets form a Venturi passage in open position. Thus, a beneficial pressure distribution is obtained and the leaflets are stabilised in opened position. (ii) The orifice inlet is nozzle-shaped. Flow is convectively accelerated and flow separation at the orifice inlet is avoided. (iii) The hinge design facilitates an additional axial movement of the leaflets and leads to a self cleaning effect and enhances washout of the hinges. The design of the leaflet hinges is of main importance for the functional reliability and durability of mechanical heart valves. After manufacturing first prototypes from titanium and polymeric materials the hydrodynamic performance was evaluated according to ISO 5840 and FDA guidelines. Hydrodynamic performance is comparable with the results of commonly available bileaflet mechanical heart valve prostheses. Initial durability tests showed suitable material couples for further long term studies.

Biocompatible Materials↗
PubMed2005

Psychoacoustic quantification of mechanical heart valve noise.

BACKGROUND AND AIM OF THE STUDY: Mechanical heart valves produce short clicking sounds during closure. These closing sounds are annoying for some patients and their partners by causing sleeping disorders or social embarrassment. Various methods for measuring the sounds have been developed both in vitro and in vivo using calculation of A-weighted sound pressure level or loudness according to ISO 532 B. The study aim was to evaluate the relevance of different psychoacoustic parameters in the evaluation of closing sounds. METHODS: Closing sounds were recorded from patients with ATS valves (n = 13), On-X valves (n = 18) and St. Jude Medical heart valve prostheses (n = 16). The sounds were recorded 5 cm above the chest of patients in a supine position, in a sound-insulated chamber. The mean peak values of loudness and sharpness were calculated and used to determine the psychoacoustic annoyance using a modification of the Widmann formula. This was verified by a listening test for ranking closing sounds of different level and sharpness by annoyance. RESULTS: There was no statistically significant independence between loudness difference or psychoacoustic annoyance difference and agreement among the test persons. For the valves, loudness ranged from 0.07 to 2.57 sone, and the psychoacoustic annoyance from 0.1 to 5.4. CONCLUSION: The results of this study showed that both sharpness and loudness have a significant influence on annoyance from closing sounds from mechanical heart valves, and indicated that the substantial variation in the parameters may be due to individual patient physiology.

Adult↗
PubMed2001

A new semi-automatic endothelial cell seeding technique for biological prosthetic heart valves.

BACKGROUND: Until today, tissue heart valve prostheses have been made with biological dead porcine or bovine tissue. However, the durability of this tissue is limited due to degeneration and calcification. Surface seeding with vital human endothelial cells (EC) could improve valve durability and bio-compatibility. A new seeding technique that includes a newly developed special seeding device is presented here. METHODS: The aortic valve, including a cylinder of the aortic root, was prepared from a fresh porcine heart taken from the slaughterhouse. Porcine endothelial cells were removed by surface treatment with chemical detergent solutions. A new seeding device with an integrated CO2-incubator was designed. The device is composed of: the seeding chamber (SC), the rotation unit (RU), and the Control Unit (CU). The porcine aortic root cylinder with the valve leaflets is placed into the SC. A matrix of fibronectin is applied to the acellular valve. The SC is then filled with the endothelial cells suspended in modified Dulbecco's eagle medium (DMEM). Under cell culture conditions, the endothelial cell seeding of the tissue valve is established by rotating the valve around two orthogonal axes simultaneously and independently. This is done following the software controlled preset parameters. RESULTS: Using initial endothelial cell seeding concentrations of 6x10(6) endothelial cells/ml DMEM, it was possible to achieve a seeding efficiency of 80-85% within 3-4 hrs. Cell viability tests proved that 90-95% of the seeded endothelial cells are vital after the seeding procedure. CONCLUSIONS: This new seeding technique allows the complex warped surface of a tissue heart valve to be covered with vital endothelial cells to form a confluent endothelial cell monolayer.

Animals↗
PubMed2004

A field of myocardial-endocardial NFAT signaling underlies heart valve morphogenesis.

The delicate leaflets that make up vertebrate heart valves are essential for our moment-to-moment existence. Abnormalities of valve formation are the most common serious human congenital defect. Despite their importance, relatively little is known about valve development. We show that the initiation of heart valve morphogenesis in mice requires calcineurin/NFAT to repress VEGF expression in the myocardium underlying the site of prospective valve formation. This repression of VEGF at E9 is essential for endocardial cells to transform into mesenchymal cells. Later, at E11, a second wave of calcineurin/NFAT signaling is required in the endocardium, adjacent to the earlier myocardial site of NFAT action, to direct valvular elongation and refinement. Thus, NFAT signaling functions sequentially from myocardium to endocardium within a valvular morphogenetic field to initiate and perpetuate embryonic valve formation. This mechanism also operates in zebrafish, indicating a conserved role for calcineurin/NFAT signaling in vertebrate heart valve morphogenesis.

Animals↗
PubMed1999

[Low molecular heparin in a pregnant women with heart valve prosthesis].

Women with a prosthetic heart valve who wish to bear a child face a difficult choice. Continued medication with warfarin during pregnancy will offer her a reasonable good protection against thrombosis, but carries a considerable risk of teratogenic effects. Subcutaneously administered heparin is an alternative to warfarin. Standard (unfractionated) heparin has not offered sufficient protection against valve thrombosis, which may be a life-threatening complication. We were contacted by a woman who wished to become pregnant and who did not want to use warfarin if this implied a risk for the foetus. We followed a protocol using low molecular weight heparin in rather high doses. The dose was adjusted according to the results of blood test controls, which confirmed increased need for anticoagulation as the pregnancy evolved. Serial eccocardiography excluded valve thrombosis. The woman needed psychological support from her general practitioner. No complications occurred, and she gave birth to a normal child. We describe the various alternatives for anticoagulant treatment in pregnant women with mechanical heart valves. The choice of anticoagulant regimen and their consequences must be thoroughly discussed with the woman.

Adult↗
PubMed1994

Cavitation dynamics of mechanical heart valve prostheses.

Nine different mechanical mitral heart valves were chosen in order to study cavitation dynamics in detail in an in vitro flow system simulating a single event of mitral valve closure. The transvalvular pressure (ventricular minus atrial pressure) rise rate averaged during the valve closing period was used as an index of the loading rate. A series of photographs in the vicinity of the inflow surface of the valve were attempted during the bubble appearance period using a stroboscopic visualization technique. The in vitro study revealed three sources of cavitation initiation in the design of the mechanical heart valves tested: stop (seat stop or seating lip), inflow strut, and clearance (gap formed between the occluder and the housing or between the two occluders in the closed position). Among these, the occluder stop design was the most critical to cavitation since all valves having the stop at the edge of the major orifice area showed a higher intensity of cavitation and threshold loading rates below the estimated normal physiological value. The analysis of bubble locations and dynamics led us to propose that the fluid squeezing effect between the occluder and the stop in the housing and the streamline contraction effect along the clearance are factors responsible for cavitation incipience.

Heart Valve Prosthesis↗
PubMed2005

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.

Animals↗
PubMed1997

Penetration of teicoplanin into heart valves and subcutaneous and muscle tissues of patients undergoing open-heart surgery.

Penetration of teicoplanin into serum, heart valves, and subcutaneous and muscle tissues was determined in 22 patients undergoing open-heart surgery. Each patient received 12 mg of teicoplanin per kg of body weight as a 30-min intravenous infusion preoperatively. Within 10 h, serum concentrations of teicoplanin declined from 43.1 to 2.8 microg/ml. Teicoplanin concentrations in subcutaneous tissues reached their peak of 9.2 microg/g after 2 to 3 h and decreased slowly to 2.3 microg/g after 9 to 10 h. Concentrations in muscle decreased from 8.7 microg/g to nondetectable levels. Teicoplanin concentrations in cardiac valvular tissue reached their peak of 6.1 microg/g and decreased thereafter to 1.7 microg/g. Teicoplanin concentrations in heart valves were high enough to inhibit methicillin-resistant Staphylococcus aureus and coagulase-negative staphylococci, which are known to cause postoperative wound infections and infective endocarditis.

Aged↗
PubMed2006

Selection of prosthetic heart valves.

Cardiovascular surgery for the repair or replacement of diseased heart valves has continually improved since its introduction in the early 1960s. Despite advances in prosthetic heart valve design, to date there is no valve that is comparable to the native human valve with respect to durability, risk of thrombosis, and overall hemodynamic function. Although bioprosthetic devices are similar to the native valve with respect to thrombogenicity, durability is a significant concern, particularly in younger patients. Approximately 45% of implanted bioprosthetic valves fail at 10 years. In contrast, mechanical prostheses have a significantly lower incidence of structural failure, with an implantation life of greater than 20 years, and are thus more often used for patients under the age of 65. Unfortunately, significant hemodynamic and thrombotic issues have yet to be resolved with the latest generation of mechanical valves. Thus, careful analysis of patient factors and valve-related complications must be considered when treatment of heart valve disease is offered to the patient. The purpose of this review is to discuss the current recommendations for surgical intervention for heart valve disease.

Journal Article↗
PubMed2006

Hearts and bones: shared regulatory mechanisms in heart valve, cartilage, tendon, and bone development.

The mature heart valves are dynamic structures composed of highly organized cell lineages and extracellular matrices. The discrete architecture of connective tissue within valve leaflets and supporting structures allows the valve to withstand life-long functional demands and changes in hemodynamic forces and load. The dysregulation of ECM organization is a common feature of heart valve disease and can often be linked to genetic defects in matrix protein structure or developmental regulation. Recent studies have identified specific regulatory pathways that are active in the developing valve structures and also control cartilage, tendon, and bone development. This review will focus on the regulatory hierarchies that control normal and abnormal heart valve development in parallel with other connective tissue cell types.

Aggrecans↗
PubMed2005

[Reimplantation of heart valve prosthesis at the 25th week of gestation].

OBJECTIVE: Pregnancy in a woman with thrombosis of heart valve prosthesis at the 25th week of gestation and fetal death during reimplantation of prosthesis with the use of extracorporeal circulation. SUBJECT: Case report. SETTING: Department of Gynecology and Obstetrics, 2nd Medical Faculty of Charles University, Motol Hospital, Prague. SUBJECT AND METHOD: Patient L. S., 24 years old, first pregnancy, admitted to coronary heart unit at the 25th week of gestation with a blocked heart valve prosthesis, NYHA IV, left heart failure, and pulmonary edema. There was an insufficient anticoagulation therapy during pregnancy and a thrombosis of the prosthetic heart valve was suspected from that reason. Reimplantation of a prosthetic heart valve with the use of extracorporeal circulation was indicated in spite of a possible risk for the fetus. The thrombosis was confirmed during cardio surgical operation and a change of the prosthesis was successfully performed. After the patient was converted to extracorporeal circulation, bradycardia and intrauterine fetal death occurred. With regard to the patient's coagulation and circulatory instability, further management was necessary because of fetal death--termination of pregnancy by minor caesarean section was the only alternative. Six hours later an 850 g weight dead fetus was delivered. There were no serious complications during the postoperative period. CONCLUSION: Reimplantation of a prosthetic heart valve from vital indication was performed at the 25th week of gestation. After conversion of mother to extracorporeal circulation, fetal death occurred. The patients was released with satisfactory cardiopulmonal compensation.

Adult↗
PubMed1982

[Risks and prognosis for success of a pregnancy following replacement of a heart valve (author's transl)].

After replacement of a heart valve a pregnancy is possible in the complaint categories I and II. Treatment with anti-coagulation is necessary for plastic heart valves. To avoid teratogenic effects the early pregnancy is best managed with heparin although stillbirth and early intra-uterine death are more common than with Marcumar. A treatment with heparin 10,000 units subcutaneously twice throughout all of the pregnancy is recommended. According to the literature 2/3 of the pregnancy with anti-coagulation result in the normal delivery of a healthy infant. Of 202 women in the reproductive age group with artificial heart valves, 150 were followed by a questionnaire. 25 women desired children. 10 women had pregnancies. 1 had two pregnancies, 1 had three pregnancies, 3 healthy infants were born.

Abnormalities, Drug-Induced↗
PubMed1992

New aspects of the degeneration of bioprosthetic heart valves after long-term implantation.

Bioprosthetic heart valves removed 76 to 150 months after implantation were morphologically investigated to correlate structural alterations with clinical failure modes. Traditional morphologic methods of evaluating valvular heterografts, such as microradiography and electron microscopy, were complemented by undecalcified ground sections, a new technique for analyzing the distribution of mineral deposits. Apart from well-investigated mechanisms that accelerate tissue degeneration, our observations point to additional facts: (1) phagocytosis of collagen fibrils and elastic material by macrophages and foreign body giant cells in areas near tears and perforations and (2) initial calcification indicated by delicate crystals in the intercellular space arranged in close relation to the periodicity of the cross-striation pattern of collagen fibrils. The present report not only calls attention to degenerative changes that are enhanced by mechanical stress but also underlines phagocytosis as an important mechanism in the destruction of bioprosthetic heart valves.

Bioprosthesis↗