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At least 667 records · Page 37Linked to original sources
PubMed2005

Tissue engineering of human heart valve leaflets: a novel bioreactor for a strain-based conditioning approach.

Current mechanical conditioning approaches for heart valve tissue engineering concentrate on mimicking the opening and closing behavior of the leaflets, either or not in combination with tissue straining. This study describes a novel approach by mimicking only the diastolic phase of the cardiac cycle, resulting in tissue straining. A novel, yet simplified, bioreactor system was developed for this purpose by applying a dynamic pressure difference over a closed tissue engineered valve, thereby inducing dynamic strains within the leaflets. Besides the use of dynamic strains, the developing leaflet tissues were exposed to pre-strain induced by the use of a stented geometry. To demonstrate the feasibility of this strain-based conditioning approach, human heart valve leaflets were engineered and their mechanical behavior evaluated. The actual dynamic strain magnitude in the leaflets over time was estimated using numerical analyses. Preliminary results showed superior tissue formation and non-linear tissue-like mechanical properties in the strained valves when compared to non-loaded tissue strips. In conclusion, the strain-based conditioning approach, using both pre-strain and dynamic strains, offers new possibilities for bioreactor design and optimization of tissue properties towards a tissue-engineered aortic human heart valve replacement.

Aortic Valve↗
PubMed2001

[INR self-management after mechanical heart valve replacement: ESCAT (Early Self-Controlled Anticoagulation Trial)].

Severe thromboembolic and hemorrhagic complications following mechanical heart valve replacement essentially occur due to intense oral anticoagulation and fluctuating individual INR values around the target range. INR self-management can help to minimize these fluctuations. Beginning this therapeutic control immediately after mechanical heart valve replacement further reduces anticoagulant-induced complications. Included in the study were 1200 patients. The quality of oral anticoagulation also improved through INR self-management. Over an observation period of two years, nearly 80% of INR values recorded by the patients themselves were within the target therapeutic range of 2.5-4.5. This corresponds to a high significance of p < = 0.001 in favor of INR self-management. Only 64.9% of INR values monitored by family practitioners were within the desired range. The results differed slightly in quality between patient groups with different levels of training (comprehensive, secondary modern, grammar with or without university). Of patients trained in INR self-management following mechanical heart valve replacement, 91.7% maintained their competence in this technique throughout the entire follow-up period. Only 8.3% of those trained immediately after surgery were unable to continue with INR self-management.

Administration, Oral↗
PubMed2006

Anticoagulation therapy during pregnancy of patients with artificial heart valves: fetomaternal outcome.

OBJECTIVES: The major problem is the need for anticoagulant therapy in patient with mechanical heart valves. STUDY DESIGN: The aim of the study was to analyze the course and outcome of pregnancies of patients with artificial mechanical heart valves with anticoagulant therapy. Study included 43 pregnancies leaded and terminated at the Institute of Gynecology and Obstetrics Clinical Center of Serbia in 20 years. We divided the patients in two groups depending on the type of anticoagulation therapy. Group I included 21 patients who were under Ethylbiscumacetate (Pelenthan) during the first 36 weeks of gestation, and intravenous Heparin in the last 4 weeks and after the delivery. Group II included 22 patients who received oral anticoagulant therapy all the time. RESULTS: Worsening of the heart functional status happened in 6 patients (13.9%). The incidence of heart failure during the pregnancy was 13.9% and after the delivery 9.3%. The incidence of hemorrhagic complications was 11.6% during pregnancy and 14% after the delivery. Four patients had thromboembolic events before the pregnancy. The incidence of postpartal thromboembolic complications was 6.9% in group I. Two patients died due to the heart failure 3-7 days after the vaginal delivery. Maternal mortality was 4.6%. One neonatus died of hydrocephalus (2.5%) in group II. In our study there were no fetuses with congenital heart disease. CONCLUSIONS: Pregnancies of patients with mechanical heart valves should be planned. We suggest ethylbiscumacetate in combination with Heparin as anticoagulation therapy during the pregnancy.

Adult↗
PubMed1994

In vitro heart valve testing: steady versus pulsatile flow.

The design of artificial heart valves has traditionally been based on the development of a prototype device which was then subjected to extensive laboratory testing in order to confirm its suitability for clinical use. In the past the in vitro assessment of a valve's performance was based principally on the measurement of parameters such as pressure difference, regurgitation and, more recently, energy losses. Such measurements can be defined as being at the 'macro' level and rarely show any clinically significant differences amongst currently available prostheses. The analytical approach to flow through heart valves has previously been hampered by difficulties experienced in solving the relevant equations of flow particularly in the case of pulsatile conditions. Computational techniques are now available which enable appropriate solutions to be obtained for these problems and consequently provide an opportunity for detailed examination of the 'micro' level of flow disturbances exhibited by the different valves. This present preliminary study is designed to illustrate the use of such an analytical approach to the flow through prosthetic valves. A single topic has been selected for this purpose which is the comparative value of steady versus pulsatile flow testing. A bileaflet valve was chosen for the analysis and a mathematical model of this valve in the aortic position of the Sheffield Pulse Duplicator was created. The theoretical analysis was carried out using a commercially available Computational Fluid Dynamics package, namely, FIDAP, on a SUN MICROSYSTEMS 10-30 workstation.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1996

In vitro function and durability of a polyurethane heart valve: material considerations.

BACKGROUND AND AIMS OF THE STUDY: Flexible trileaflet polyurethane heart valves can be designed which have good hydrodynamic function in vitro. The choice of polyurethane for fabrication of such valves is not simple; several similar polyurethanes are available, but relatively minor differences in their structure and composition may have profound effects on long term fatigue behavior with little effect on their short term mechanical properties. METHODS: The relative functional characteristics of flexible trileaflet polyurethane valves made from two different polyetherurethanes were compared before and after long term fatigue testing. The polyetherurethanes had similar gross mechanical properties, differing in that one was chain-extended with butanediol (PEU) and the other with ethylene diamine (PEUE). Six valves of each type, with similar leaflet thickness distributions, were studied. RESULTS: Hydrodynamic function of both valve types was similar to a similarly sized porcine aortic valve. Mean pressure drop across the open valve was higher in PEU valves than in PEUE valves, although PEUE valves had greater energy losses during closure and when closed. Reverse flow decreased with time in the fatigue tester. In long term fatigue tests, all six PEU valves failed by 307 million cycles, with failure primarily by development of holes at the coaptation region of the leaflets associated with localized calcification. Three PEUE valves exceeded 800 million cycles without failure and all PEUE valves exceeded 450 million cycles. CONCLUSIONS: A combination of good phase separation of polyurethane soft and hard segments with good rubbery characteristics can explain the better results achieved in the PEUE valves compared with similar PEU valves. These results suggest the general type of polyurethane structure suitable for heart valve fabrication and have implications for development of novel polyurethanes for this application.

Animals↗
PubMed1992

[Heart valve substitution: the effect of preoperative findings on long-term outcome].

BACKGROUND: In a retrospective analysis of 653 consecutive patients who underwent heart valve replacement by one single type of mechanical prosthesis (St. Jude Medical) at three Swiss university medical centers (Basel, Bern, Lausanne), the outcome was judged on the basis of preoperative variables. These variables should facilitate the timing of heart valve replacement. METHODS: Preoperative evaluation includes NYHA classification of symptoms, chest X-ray, ECG, and LVEF on angiography. Postoperative outcome was assessed clinically at yearly intervals by NYHA classification, documentation of complications and mortality. RESULTS: Five-year-survival rates were 96 and 88%, and complication-free rates were 82 and 76% respectively in patients after isolated aortic and mitral valve replacement. An unsatisfactory outcome with death or persistent severe symptoms was more frequent when preoperative symptoms at rest and atrial fibrillation were present. CONCLUSION: Heart valve replacement should not be postponed until severe symptoms and functional impairment occur. Clinical criteria are at least as important for the timing of operation as the findings of more complex investigations.

Adolescent↗
PubMed1996

Scaling of mechanical heart valves for cavitation inception: observation and acoustic detection.

This paper discusses scaling laws of cavitation in mechanical heart valves based on analysis of leaflet operation and on hydrodynamic theory. It then suggests the laboratory use of large geometric scales and testing at low operating pressures to more easily investigate new heart valve designs. With such scaling, observations and measurements will become easier since the cavitation regions will be larger in dimension and the time scales will be increased due to reductions of bubble characteristic times and leaflet oscillation periods. The paper also discusses cavitation noise and the potential for acoustic detection of cavitation in a mechanical heart valve.

Biophysical Phenomena↗
PubMed1986

Reoperation for prosthetic heart valve replacement.

From 1974 to 1984, 847 heart valve replacement operations were performed with 1005 prosthetic valves. Thirty-nine (4.6%) were reoperations with 43 prosthetic valve replacements (PVR), on 38 patients. Thirty-three patients had received their initial valve replacement in our hospital and 5 elsewhere. Twenty additional cardiac procedures were required, concomitantly with the prosthesis replacement. Twenty-three patients underwent replacement of a mechanical prosthesis (61%) an average of 4.3 years after initial implantation and 15 patients a bioprosthesis (39%) after 2.8 years. Indications for PVR were endocarditis in 15 patients (39%), prosthesis failure in 13 (34%), periprosthetic leak in 7 (18%), thrombosis in 2 (5%), and a left ventricle subannular aneurysm in 1 (3%). Preoperatively 4 patients were in NYHA functional class II (11%), 15 in class III (39%) and 19 in class IV (50%). Six patients died early postoperatively (15.8%) Various risk factors were analyzed. The early mortality rate was 22% for mechanical prosthesis replacement and 7% for bioprosthesis; 11% for aortic position, 13% for mitral position and 50% to 100% for double valve replacement; 23% for non-elective and 6% for elective operations; 10% for patients with only an initial valve replacement and 43% with additional previous valve operations; 18% for active endocarditis, 15% for prosthesis failure, 14% for periprosthetic leak, 0% for thrombosis and 100% for subannular aneurysm; 0% for patients in class II, 7% in class III and 26% in class IV; 6% in patients with an aortic cross-clamp time less than 2 hours and 24% with more; 27% prior to 1981 and 9% during the last 4 years; and finally 50% in patients over the age of 60.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1980

Leucocyte migration inhibition with human heart valve glycoproteins and group A streptococcal ribonucleic acid proteins in rheumatic heart disease and post-streptococcal glomerulonephritis.

Leucocyte migration inhibition (LMI) tests have been performed with leucocytes obtained from patients with acute rheumatic carditis, established rheumatic valvular disease with and without rheumatic reactivation, post-streptococcal glomerulonephritis and healthy volunteers, using human heart valve glycoprotein (HVGP) antigens and ribonucleic acid protein antigens (P-RNA) from Group A streptococci, types 5, 6 and 12 and a Group C streptococcus. Significantly increased LMI was observed with HVGP and P-RNA antigens of Group A streptococci in patients with clinical evidence of rheumatic valvular damage. Healthy volunteers and patients with poststreptococcal glomerulonephritis did not show any increase in LMI to these antigens. This suggests that cell-mediated immune mechanisms may be involved in the production of tissue lesions in rheumatic fever.

Adolescent↗
PubMed2004

Observation of cavitation bubbles in monoleaflet mechanical heart valves.

Recently, cavitation on the surface of mechanical heart valves (MHVs) has been studied as a cause of fractures occurring in implanted MHVs. In the present study, we investigated the mechanism of MHV cavitation associated with the Björk-Shiley valve and the Medtronic Hall valve in an electrohydraulic total artificial heart (EHTAH). The valves were mounted in the mitral position in the EHTAH. The valve closing motion, pressure drop measurements, and cavitation capture were employed to investigate the mechanisms for cavitation in the MHV. There are no differences in valve closing velocity between the two valves, and its value ranged from 0.53 to 1.96 m/s. The magnitude of negative pressure increased with an increase in the heart rate, and the negative pressure in the Medtronic Hall valve was greater than that in the Björk-Shiley valve. Cavitation bubbles were concentrated at the edge of the valve stop; the major cause of these cavitation bubbles was determined to be the squeeze flow. The formation of cavitation bubbles depended on the valve closing velocity and the valve leaflet geometry. From the viewpoint of squeeze flow, the Björk-Shiley valve was less likely to cause blood cell damage than the Medtronic Hall valve in our EHTAH.

Equipment Failure Analysis↗
PubMed2004

Anticoagulation in pregnant women with prosthetic heart valves.

BACKGROUND: Pregnancy is associated with an increased risk of thrombosis in women with mechanical prosthetic heart valves. Effective anticoagulation is therefore critical in such patients but remains problematic, since oral anticoagulation and both unfractionated and low-molecular-weight heparin may be associated with important fetal and maternal side effects. PURPOSE: To review information related to the use of anticoagulation with both warfarin and heparin and reassess the safety and efficacy of these therapies in pregnant women with mechanical prosthetic heart valves. DATA SOURCE AND SELECTION: A MEDLINE search from 1966 to October 2003 for English and non-English language articles that reported the use of anticoagulation in pregnancy was conducted. Articles were included if they reported use of anticoagulation in pregnancy with emphasis on those that included women with mechanical prosthetic heart valves. CONCLUSIONS: Anticoagulation prophylaxis with both warfarin and heparin (unfractionated heparin and low-molecular-weight heparin) may be associated with important fetal and maternal side effects. Optional regimens for the treatment of low-risk and high-risk patients are proposed to minimize potential complications.

Adult↗
PubMed2000

New pulsatile bioreactor for in vitro formation of tissue engineered heart valves.

Two potential obstacles to the creation of implantable tissue engineered heart valves are inadequate mechanical properties (ability to withstand hemodynamic stresses) and adverse host-tissue reactions due to the presence of residual nondegraded polymer scaffold. In an attempt to address these problems, we developed an in vitro cell culture system that provides physiological pressure and flow of nutrient medium to the developing valve constructs. It is anticipated that in vitro physical stress will stimulate the tissue engineered heart valve construct to develop adequate strength prior to a possible implantation. Long-term in vitro development will be realized by an isolated and thereby contamination-resistant system. Longer in vitro development will potentially enable more complete biodegradation of the polymeric scaffold during in vitro cultivation. This new dynamic bioreactor allows for adjustable pulsatile flow and varying levels of pressure. The system is compact and easily fits into a standard cell incubator, representing a highly isolated dynamic cell culture setting with maximum sterility, optimal gas supply and stable temperature conditions especially suited for long-term experiments.

Animals↗
PubMed2004

[Models of inter-group difference of the homeostasis system in patients with artificial heart valves and the set of laboratory parameters].

Patients with artificial heart valves (AHV) belong to a unique multi-component model of the homeostasis system presenting an interaction of activated coagulation processes and pharmacological effects, on the one hand, and genetic peculiarities functioning homeostatic mechanisms, on the other hand. The described method was evaluated on the basis of multi-factor mathematic analysis by information-metry. The data obtained provided for isolating the most information-dense laboratory indices and some genetic polymorphisms describing the shaping of continuous intravascular coagulation of stage III in AHV patients. The clinicians and laboratory experts are offered a practical instrument for the diagnosis (prognostication) of the above condition. It was proven as necessary to examine (by the morphofunctional method) the intravascular activation of platelets and to determine the D-dimer in the remote period after prosthesis of heart valves.

Clinical Laboratory Techniques↗
PubMedDate not supplied

Thrombogenic performance of a st. Jude bileaflet mechanical heart valve in a sheep model.

The sheep model is preferred for chronic evaluation of prosthetic heart valves, surgical techniques, and endocardiographic studies. A bileaflet mechanical heart valve (MHV) was implanted into a sheep model to study its in vivo performance and to evaluate the thrombogenic potential of the valve. Transesophageal echocardiography and transcranial Doppler ultrasonography measurements were conducted before and after the valve implantation. Platelet activity state (PAS) assay measurements were also conducted before and after the implantation surgery. After sheep euthanasia, the MHV was explanted and scanning electron microscopy (SEM) was performed on the explanted valve to examine changes to the MHV surface. Tissue blocks were taken from the sheep brain, left ventricle, aorta, spleen, and lung lobes for histological examination. Our results indicated that after the MHV implantation, more embolic signals were detected in the sheep carotid artery, increasing monotonously as a function of implantation time. Echocardiographic parameters including blood aortic velocity, transvalvular pressure gradient, and velocity time integral increased. PAS increased significantly after valve implantation. SEM pictures demonstrated calcium and phosphate deposition on the valve surfaces. Histological examination demonstrated hemorrhage in the lung tissue, pulmonary thrombosis, and osteogenesis in heart tissue.

Animals↗
PubMed2006

Decellularized xenogenic heart valves reveal remodeling and growth potential in vivo.

We have developed an advanced tissue processing technique on porcine pulmonary heart valves for pulmonary valve replacement and its initial clinical application during the autograft operation according to Ross. The novel concept consists of a cell-free matrix achieved by deoxycholic acid treatment that is repopulated by host cells in vivo. Molecular biology, radioligand binding, and electron microscopy consistently showed that these valves are almost free of cellular components. Animal experiments and clinical investigations revealed excellent hemodynamic properties of the valves, no need for antithrombotic therapy, and repopulation by host cells without any signs of calcification. In juvenile sheep the internal diameter of the implanted valves significantly increased in growing animals by approximately 10 mm. The repopulation of the decellularized heart valves was found not only in sheep but also in humans, which indicates that the underlying mechanisms, presumably repair mechanisms, might be common in mammals. If these findings can be confirmed by others, they will lead to new concepts in the field of cardiovascular tissue engineering that will eliminate the need for in vitro construction of autologous heart valves.

Animals↗