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At least 199 records · Page 11Linked to original sources
PubMed2003

Anticoagulant therapy in pregnant women with mechanical heart valves.

Managing women with mechanical heart valves during pregnancy poses a particular challenge as there are no available controlled clinical trials to provide guidelines for effective antithrombotic therapy. Oral anticoagulation with coumadin-derivates administration is associated with coumarin embryopathy, and subcutaneous administration of unfractioned heparins (UFH) has been reported to be ineffective in preventing thromboembolic complications. Due to the increased risk of thromboembolic events when UFH is used, low molecular weight heparins (LMWH) were considered to be an alternative. The evidence in the literature regarding the long-term use of LMWH as the only anticoagulant after mechanical heart valve replacement is limited only to a few reports encompassing only 25 patients, with treatment failure in 20%. These data show that anticoagulation with LMWH only is neither safe nor effective in preventing thromboembolic events after mechanical heart valve replacement, in pregnant or non-pregnant women.

Anticoagulants↗
PubMed2006

Percutaneous replacement of pulmonary valve using the Edwards-Cribier percutaneous heart valve: first report in a human patient.

We report on the use of the Edwards-Cribier percutaneous heart valve (PHV) in a stenotic right ventricle to pulmonary artery homograft in a 16-year old patient who underwent the Ross operation. Initially, the homograft was stented and at the same procedure, the PHV was deployed inside it. This is the first human case of the application of this valve in the pulmonary valve position.

Adolescent↗
PubMed2000

A new method for quantitative evaluation of perceived sounds from mechanical heart valve prostheses.

Closing clicks from mechanical heart valve prostheses are transmitted to the patient's inner ear mainly in two different ways: as acoustically transmitted sound waves, and as vibrations transmitted through bones and vessels. The purpose of this study was to develop a method for quantifying what patients perceive as sound from their mechanical heart valve prostheses via these two routes. In this study, 34 patients with implanted mechanical bileaflet aortic and mitral valves (St Jude Medical and On-X) were included. Measurements were performed in a specially designed sound insulated chamber equipped with microphones, accelerometers, preamplifiers and a loudspeaker. The closing sounds measured with an accelerometer on the patient's chest were delayed 400 ms, amplified and played back to the patient through the loudspeaker. The patient adjusted the feedback sound to the same level as the 'real-time' clicks he or she perceived directly from his or her valve. In this way the feedback sound energy includes both the air- and the bone-transmitted energies. Sound pressure levels (SPLs) were quantified both in dB(A) and in the loudness unit sone according to ISO 532B (the Zwicker method). The mean air-transmitted SPL measured close to the patient's ear was 23 +/- 4 dB(A). The mean air- and bone-transmitted sounds and vibrations were perceived by the patients as an SPL of 34 +/- 5 dB(A). There was no statistically significant difference in the perceived sound from the two investigated bileaflet valves, and no difference between aortic and mitral valves. The study showed that the presented feedback method is capable of quantifying the perceived sounds and vibrations from mechanical heart valves, if the patient's hearing is not too impaired. Patients with implanted mechanical heart valve prostheses seem to perceive the sound from their valve two to three times higher than nearby persons, because of the additional bone-transmitted vibrations.

Acoustics↗
PubMed2000

Low molecular weight heparin after mechanical heart valve replacement.

BACKGROUND: Patients with mechanical heart valves require life-long anticoagulation. We report here the first large and comparative series of consecutive patients anticoagulated with low molecular weight heparin (LMWH) after mechanical heart valve replacement. METHODS AND RESULTS: In this comparative, nonrandomized study, 208 consecutive patients who underwent a single or double heart valve replacement with mechanical prostheses were anticoagulated subcutaneously with unfractionated heparin (UH) in the first period (n=106) and LMWH in the second phase (n=102) of the study. Baseline characteristics were similar in the 2 groups. The mean durations of UH and LMWH treatments were 13.6+/-0.5 and 14.1+/-0.6 days, respectively (not significant). On the second day of treatment, 87% of patients treated with LMWH had an anti-Xa activity within the range of efficacy (0.5 to 1 IU/mL), but only 9% of UH-treated patients had an activated partial-thromboplastin time value within the therapeutic range (1.5 to 2.5 times control, P<0.0001 between the 2 groups). On the last day of prescription, all LMWH-treated patients had anti-Xa activity above 0.5 IU/mL, but 19% were above 1 IU/mL. In the UH group, 27% of patients had an activated partial-thromboplastin time above 1.5 times control, but 62% were overanticoagulated. Two major bleedings occurred in each group, and one stroke occurred in the UH group. CONCLUSIONS: In this first comparative study, anticoagulation with LMWHs after mechanical heart valve replacement appears feasible, provides adequate biological anticoagulation, and compares favorably with UH anticoagulation. Randomized studies are now needed to further evaluate this new therapeutic approach.

Anticoagulants↗
PubMed2002

A broad and strong humoral immune response to donor HLA after implantation of cryopreserved human heart valve allografts.

Cryopreserved human heart valves are used for valve replacement in patients with congenital or acquired heart disease. Although no blood group or human leukocyte antigens (HLA) matching is performed and no immunosuppression is administered, the clinical results are relatively good. After valve replacement, the majority of the patients develop HLA antibodies, whereas a smaller group of patients shows valve-related events at the long term after right ventricular outflow tract reconstruction. Therefore, we hypothesized that not the mere presence, but rather the titers of antidonor HLA antibodies may be related to valve allograft failure. The presence and specificity of HLA class I antibodies were determined by complement-dependent microlymphocytotoxicity (CDC) test in longitudinally taken peripheral blood samples of 35 valve allograft recipients. In eight patients with an antibody response specific against donor-HLA class I, the titers were measured by this CDC method after stepwise dilution of the plasma. Panel reactive antibodies of more than 10% were found in 31 of 35 (89%) valve allograft recipients. From these 31 patients, 24 (77%) developed donor-specific HLA class I antibodies. All eight selected patients had detectable donor-specific antibody titers, ranging from 1:2 to 1:8,000. Two donor valve recipients before retransplantation had (donor-specific) HLA antibodies and showed high titers of 1:256 and 1:8,000 shortly after the second allograft valve replacement, which was associated with an early graft failure in the latter patient. We conclude that transplantation of cryopreserved human heart valve allografts leads to a broad and strong humoral response, which is probably the result of a lack of immunosuppressive therapy after valve transplantation. Patients receiving a second or following valve allograft appeared to be sensitized and developed early and high allo-antibody titers after second valve allograft implantation. Valve failure was diagnosed in a patient with extremely high titers. These findings suggest that preoperative cross-matching may identify patients with high donor-specific HLA antibody titers and may reduce the risk for early recurrent graft failure.

Adolescent↗
PubMed2002

Caring for patients with prosthetic heart valves.

Patients with prosthetic heart valves require regular examinations and echocardiograms, antithrombotic therapy, and appropriate antibiotic prophylaxis against endocarditis. Physicians must also be on the alert for several uncommon but potentially devastating complications: valve structural failure, thrombosis, embolism, endocarditis, paravalvular leak, and hemolytic anemia.

Heart Valve Diseases↗
PubMed2001

A new design for polyurethane heart valves.

BACKGROUND AND AIM OF THE STUDY: The synthetic flexible tri-leaflet heart valve offers considerable potential for improvement in both hydrodynamic and biomechanical performance of replacement heart valves. To date, success with the synthetic leaflet heart valve has been limited, partly due to limitations in the biostability of the polyurethanes used. With the synthesis of new biostable polyurethanes, the integration of advancing technology, and better knowledge of the functional and biomechanical design requirements necessary to increase the long-term durability of the polyurethane heart valve, novel clinical solutions are now in sight. METHODS: This study describes the design characteristics, hydrodynamic and biomechanical performance of a new design of polyurethane heart valve. The function and durability characteristics of this novel design of heart valve, manufactured using a proven durable non-biostable polyurethane, was compared with that of a single AorTech porcine bioprosthetic heart valve and a single tilting disc mechanical heart valve, the Björk-Shiley Monostrut valve (BSM), of similar size. RESULTS: For equivalent sizes of valve, the new polyurethane heart valve design had significantly lower pressure gradients compared with the porcine valve at all flow rates and to the BSM valve at the higher flow rates. The effective orifice area of the polyurethane valve was greater than the other two valves studied; regurgitation and total energy loss were less. The new polyurethane valve design reached over 360 million cycles in an accelerated durability tester, without failure. CONCLUSION: This new design of polyurethane heart valve showed improved hydrodynamic function in comparison with either the porcine bioprosthetic or the BSM mechanical heart valve. The pulsatile flow results showed a lower total energy loss associated with this valve, indicating improved potential patient benefit. The durability of this new design of polyurethane heart valve was demonstrated when manufactured using a medical-grade polyurethane.

Biomechanical Phenomena↗
PubMedDate not supplied

Accelerated life testing of prosthetic heart valves.

Throughout the years of prosthetic heart valve development, the long-term durability of heart valve development, the long-term durability of heart valves has been studied by accelerated life-cycle testing. Accelerated testing has been used to study materials, design concepts, design modifications, and durability variations caused by changes in manufacturing techniques. As with all in vitro tests, knowledge of the limitations of the test is of paramount importance in analyzing the results. The greatest strength of the accelerated cycle test, however, lies in comparisons of one valve with another. It is in this manner that new prototypes, new materials, or slight modifications in valve design can be gauged with respect to valve life. Valves with long clinical history can be used as standards. Whether a test valve will have a longer or shorter expected life than the standard can be estimated in a relatively short period in side-by-side test runs.

Biomedical Engineering↗
PubMed2004

Recent progress in heart valve surgery: innovation or evolution?

Although heart valve surgery continues to evolve in a dynamic fashion, there is still no optimal solution for all patients. Minimally invasive surgery currently receives considerable attention but its value still needs to be determined. Progress has been made in valve repair, which now allows reconstruction in most patients with mitral valve disease. Reconstruction of the aortic valve is now also possible with results that are now comparable to those of mitral repair. In the future a wider application of repair procedures and further improvements of biologic valves can be anticipated not only to influence long-term results, but also the decision making process for conservative or surgical treatment.

Aortic Valve↗
PubMed1991

[Physiology of the heart valves].

The function of healthy heart valves has been understood as the "on-off switch", which initiates and terminates blood flow in the cardiac cycle. It is believed that an impedance of the valves against blood flow is minimal and their closure is abrupt and complete. Clinically, an increase in impedance of the diseased valve is estimated by measuring pressure difference across that valve. However, the pressure gradient induced by acceleration of blood along the outflow tract of the ventricle or the artery during the early ejection phase, or along the inflow tract of the ventricle during the rapid filling phase can not be estimated separately from the pressure difference produced by valvular impedance in physiological state. Opening speed of the valve is related to the factors determining the velocity of blood flow. Mechanisms of a valve closure have been explained based on the Henderson and Johnson's concepts. Recent advances in ultrasonic technology can only confirm their concepts. Measurement of the pressure gradient across the semilunar valves in the late ejection phase has also several technical difficulties. Relationships among pressure, flow and valve motion have been extensively investigated, how-exact determination of the timing of the valve closure is not detected. The heart valves are considered to function as a passive organ throughout the cardiac cycle except for the atrioventricular valves including the subvalvular apparatus during systolic phase. The development of new methodology is necessary for the investigation of this field.

Animals↗
PubMed2002

[Risk of second and third reoperation on prosthetic heart valves].

As the volume of heart valve replacements increases, more patients are undergoing repeated operations. There are many reasons for reoperations that include incomplete or imperfectly executed primary operation, infection on valve prostheses, valve related complications. Repeated operations have their own specific technical problems, and from them depends mortality and complications rate. At Vilnius University Heart Surgery Clinic from 1967 we performed 6200 heart valve replacement operations. At the same time we performed 428 reoperations for 394 patients. Two reoperations were performed for 28 patients and 3 reoperations for 3 patients (65 reoperations for 31 patient). Main course of reoperation - sepsis and periprosthetic leaks (50%). Half of patients at the time of last reoperation were in functional class V (NYHA). Mortality rate after second reoperation was 28%, after third reoperation all three patients died. Main course of operative mortality - sepsis, heart failure, hemorrhage.

Heart Valve Prosthesis↗
PubMed1990

Clinical problems in patients with prosthetic heart valves.

Information from the UK Heart Valve Registry, which was established in 1986 and receives data from all centres in the National Health Service, shows that more than 5,000 artificial heart valves are implanted each year in Britain and that almost two-thirds of these are mechanical. This article is intended as a practical outline of the clinical problems and complications which may occur.

Follow-Up Studies↗
PubMed1994

Confocal laser scanning microscopy of calcified bioprosthetic heart valves.

Calcification of bioprosthetic heart valves is a major factor limiting their long-term function. Current methods of microscopic examination of calcific deposits require dehydration and processing of the leaflet material, e.g. wax embedding, sectioning, gold coating. Confocal laser scanning microscopy is a new technique which allows serial optical sectioning of thick biological specimens in their normal hydrated state. The current study has examined bovine pericardium and porcine aortic valve materials calcified in vitro under static and dynamic conditions. A series of clinical explants of bovine pericardial and porcine aortic valve types has also been examined. The calcium-specific stain, Alizarin Red S, has been used as a fluorescent marker for calcium deposits. Fluorescent images, generated by Argon ion laser light at 488nm, have been obtained at varying depths into samples. These have been reconstructed to demonstrate the relationship between calcium deposits and autofluorescent collagen fibers. The patterns of calcification were similar in both in vitro and explant valve material. The calcification was of three main patterns: calcium depositing longitudinally on collagen fiber bundles; calcium forming a banded pattern perpendicular to the fiber direction and large, dense, focal deposits obliterating the underlying collagen structure. Involvement of collagen fibers in the calcification pattern was a consistent finding in all sample types. The method is a useful addition to the tools available for study of calcification processes. The potential exists for three-dimensional reconstruction of leaflet architecture and its inter-relationship with calcium deposition, in a normally hydrated state.

Adult↗
PubMed1981

Methicillin distribution in serum and extravascular fluid and its relevance to normal and damaged heart valves.

We evaluated the distribution of methicillin into normal and damaged heart valves and the accuracy with which subcutaneous plastic chambers reflected tissue uptake of this antibiotic. A total of 24 male New Zealand rabbits were given constant infusion doses of methicillin through central venous catheters. Five of these animals had their aortic and mitral valves damaged by catheterization of the left ventricle. A total of 19 rabbits had perforated plastic chambers inserted subcutaneously 7 to 10 days before methicillin infusion. In all animals more than 80% of the total infused dose of methicillin was accounted for in the serum, urine, and tissues. In the 12 animals infused to steady state (less than 7 h), the steady-state serum concentrations (11 to 120 micrograms/ml) were equal to the concentrations attained in either peritoneal or tissue chamber fluids. In the 12 animals sacrificed before 7 h, tissue chamber concentrations lagged behind serum and heart tissue concentrations in attaining steady state. Steady-state concentrations in normal heart valves and heart muscles failed to increase proportionally to increased constant infusion doses (8.7 to 87.2 mg/kg per h). The steady-state methicillin concentrations in fibrin-scarred heart valves were invariably higher than the steady-state concentrations in the normal right heart of the same animals (P less than 0.05). Tissue uptake of methicillin was altered in scarred heart valves as compared to normal heart valves, and large-volume subcutaneous tissue chambers misrepresented the uptake rate of methicillin into heart tissues and valves.

Animals↗
PubMed1993

Clinical experience with the Omnicarbon prosthetic heart valve.

The Omnicarbon prosthetic heart valve (Medical Inc., Inver Grove Heights, Minn.) was implanted in 124 patients (mean age 53 +/- 11 years); 66 of them had aortic valve replacement, 40 had mitral valve replacement, and 18 had both aortic and mitral valve replacement. Preoperatively 76.6% were in New York Heart Association class 3 or 4, and 84.7% were in class 1 or 2 after the operation. There were six (4.8%) early deaths and seven late deaths. Survival was 85% +/- 6% at 6 years in the aortic valve replacement group, 94% +/- 4% at 3 years in the mitral valve replacement group, and 78% +/- 11% at 4 years in the double valve replacement group. Freedom from cardiac death was 89% +/- 4% at 6 years (2.0% per patient-year) in the aortic valve replacement group, 94% +/- 4% at 3 years (1.8% per patient-year) in the mitral valve replacement group, and 78% +/- 11% at 4 years (5.7% per patient-year) in the double valve replacement group. There were six valve-related complications. Freedom from valve-related complications was 92% +/- 4% at 6 years (1.5% per patient-year) in the aortic valve replacement group, 97% +/- 3% at 3 years (1.8% per patient-year) in the mitral valve replacement group, and 83% +/- 11% at 4 years (5.7% per patient-year) in the double valve replacement group. Cerebral hemorrhage was seen in two patients in the aortic valve replacement group. Freedom from all events was 80% +/- 7% at 6 years in the aortic valve replacement group, 88% +/- 6% at 3 years in the mitral valve replacement group, and 78% +/- 11% at 4 years in the double valve replacement group. Elevation of the postoperative serum lactate dehydrogenase levels was minimal in all groups. The maximum opening angle at rest was 60.0 +/- 8.9 degrees in the aortic position and 54.1 +/- 6.6 degrees in the mitral position. In conclusion, the Omnicarbon prosthesis had excellent postoperative clinical status and negligible hemolysis.

Adult↗
PubMedDate not supplied

Approaching comparability and results of pulsatile flow in vitro testing of prosthetic heart valves.

The testing of prosthetic heart valves under pulsatile conditions is still a subject for debate among researchers and competent standardization bodies. The laboratory of Biomedical Engineering, of the Istituto Superiore di Sanità in Rome, has reproduced the current inter-laboratory situation with several test apparatuses, focusing on the definition of significant measurement parameters and procedures to obtain reasonably comparable data. The laboratory is also equipped with a Laser Doppler Anemometer (LDA) and a High-Speed Cinematographic system (HSC). A 29 mm tilting disc valve model, was mounted in the aortic position. Under tightly controlled system conditions the analyses performed on two pulse duplicators (PDs) may be deemed consistent for the valve model tested. Useful results, on the same valve specimen, are reported concerning velocity profiles and turbulent shear stress values (TSS). Furthermore valve motion on the Sheffield PD was monitored during the closing phase, and related cinematic data reported. The applied methodologies can provide relevant data to support surgeon decision making.

Aortic Valve↗
PubMed2004

Mechanical and structural properties of a novel hybrid heart valve scaffold for tissue engineering.

Hybrid heart valve scaffolds were fabricated from decellularized porcine aortic heart valve matrices and enhanced with bioresorbable polymers using different protocols: (i) dip coating of lyophilized decellularized matrices, and (ii) impregnation of wet decellularized matrices. The following polymers were evaluated: poly(4-hydroxybutyrate) and poly(3-hydroxybutyrate-co4-hydroxybutyrate). Tensile tests were conducted to assess the biomechanical behavior of valve leaflet strips. Suture retention strength was evaluated for the adjacent conduit. A pulse duplicator system was used for functional testing of the valves under physiological systemic load conditions. The properties of the hybrid structures were compared with native, decellularized, and glutaraldehyde-fixed specimens. Mechanisms of the polymer impregnation process were studied with IR spectroscopy, fluorescent microscopic imaging, and SEM. Altogether this study demonstrates the feasibility and improved biomechanical function of a novel hybrid heart valve scaffold for an application in tissue engineering.

Animals↗
PubMed2002

Prosthetic heart valve thrombosis: an overview.

BACKGROUND: Valvular heart disease represents a significant burden to patients with cardiovascular diseases. Surgical treatment of diseased heart valves represents a significant advancement for these patients. However, there are specific complications related to prosthetic valves, including valve thrombosis. METHODS: Review article. RESULTS: Thrombosis of a prosthetic heart valve can present with gradual cardiac decline, embolic phenomena, or frank cardiogenic shock. The diagnosis of prosthetic valve thrombosis is by history, physical examination, and by an imaging modality. Treatment of the thrombosed valve is either surgical or with thrombolysis. Both modalities have significant morbidity and mortality. CONCLUSION: Treatment of valvular heart disease does not remove the patient from significant risks. Inherent to a prosthetic heart valve is the risk for valvular thrombosis. Prompt recognition and treatment of prosthetic valve thrombosis is important.

Heart Valve Prosthesis↗