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Results for “Heart Valve Prosthesis”

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At least 19 recordsLinked to original sources
PubMed1991

Principle of operation, design criteria and fluid dynamics of a new bileaflet heart valve prosthesis.

Bileaflet heart valves show the best fluid dynamic behaviour among mechanical valves and, as a consequence, give the best clinical results. A new bileaflet heart valve has been designed whose main characteristics are the kind of leaflet movement, low profile, fluid dynamics and material. Two flat leaflets move freely inside a very low profile housing ring. The movement is described by the rolling without sliding of the leaflet surface around a cylindrical surface on the inner wall of the housing. The opening angle is 85 degrees. Both the leaflets and the housing are machined from a solid piece of titanium and then covered with carbon by ion beam techniques. The design phase and the first fluid dynamic evaluation were done by numerical methods.

Carbon↗
PubMed1992

A study of the stability of orientation in the CarboMedics bileaflet heart valve prosthesis.

A total of 25 CarboMedics bileaflet prostheses was studied in the immediate postoperative period and at 1 week, 1 month and 3 months after surgery. No evidence of rotation was found on visual comparison of valve orientation and there were no significant differences between successive studies for the distance between the septum and either the anterior (P = 0.92) or posterior leaflet (P = 1.00) of valves in the mitral position. The possibility of spontaneous rotation is a potential drawback not only of the CarboMedics prosthesis, but also of designs currently being developed. This study suggests that major rotation does not occur commonly.

Adult↗
PubMed1977

[Clinical anatomical basis of the pathogenesis of fatal complications in the late periods after heart valve prosthesis].

On the basis of clinico-anatomical analysis of the causes of death in 35 patients following valve prosthetics for rheumatic valvular disease, it was established that cardiac failure was the most frequent cause. Cardiac failure was due to exacerbation of the carditis process on the one hand, and to disorders of the rhythm induced by dystrophy, sclerosis, fibroelastosis, and calcinosis in the cardiac septum on the other. Thromboembolic processes rate second in frequency among the lethal complications. Death from septic complications was rarely encountered, and from causal causes only in individual cases.

Autopsy↗
PubMed1977

[Heart valve prosthesis in congenital heart defects].

The experience of 68 cases of prosthetic valve replacement for congenital heart diseases is presented. The majority of the cases were 57 patients with the Ebstein anomaly and tetralogy of Fallot. In the patients with the Ebstein anomaly the tricuspid valve was replaced, in those with the tetralogy of Fallot--a plastic enlargement of the pulmonary artery trunk and prosthetic replacement of the pulmonary valve with a ball valve or xeno-graft. Original techniques of radical correction of the Ebstein anomaly and tetralogy of Fallot are presented.

Adult↗
PubMedDate not supplied

The porcine heart valve prosthesis.

The development of the prosthetic heart valve has led to the evolution of cardiac intensive care units, a better understanding of cardiac function and biocompatible materials, and new surgical procedures. Initial efforts with formaldehyde-fixed valves did not have long-term success. They led to the development of the stabilized glutaraldehyde process (SGP) valve and the flexible stent. The safety and efficacy of a heart valve bioprosthesis has been demonstrated through laboratory and animal experiments. Data on long-term clinical implants are needed to validate the results of these experiments.

Animals↗
PubMed1975

Pathogenesis of fungal infection on heart valve prosthesis.

Four patients with heart valve prostheses developed Candidate endocarditis. At autopsy the foci of infection were confined to patches of neoendocardium that appeared to have developed as ingrowths of host endocardium onto the sewing cloth of the artificial valve. This suggested that one mechanism of fungal infection is related to the presence of the neoendocardium rather than to the cloth or metallic substances of the valve itself. Future studies might be directed toward inhibiting the development of the neoendocardium or to agents preventing its susceptibility to infection.

Adult↗
PubMed1976

In vivo evaluation of the Lillehei-Kaster heart valve prosthesis.

In vivo evaluation of the Lillehei-Kaster heart valve prosthesis was performed in 28 patients; 22 had undergone aortic valve replacement and 6 had had mitral valve replacement. Mean pressure gradients ranged from 6 to 53 mm Hg in aortic prostheses; valve area varied from 0.83 to 2.9 cm2. The maximum opening angle of 80 degrees was never reached in this group of patients; opening angles ranged from 57 to 74 degrees without evidence of disc malfunction. There was no correlation between the ratio of effective to geometric valve area and the degree of opening of the disc occluder. Similar results were found in the mitral valve group. Gradients ranged from 6.0 to 12.5 mm Hg and valve area from 1.6 to 2.2 cm2. The maximum opening angle was 59 to 63 degrees. It is concluded that incomplete opening of the disc occluder in pivoting-disc valves is not necessarily a sign of disc malfunction. Lillehei-Kaster valves smaller than 18 mm in internal diameter should be avoided in adults, and outflow aortoplasty for implantation of a larger prosthesis should be used in patients who have a narrow aortic root.

Adult↗
PubMed1992

Determination of markers of coagulation activation and reactive fibrinolysis in patients with mechanical heart valve prosthesis at different intensities of oral anticoagulation.

In a group of 60 patients with mechanical heart valve prosthesis prothrombin fragment 1 + 2, thrombin-antithrombin III complexes and D-dimer have been determined in order to assess the residual coagulation activation and the extent of the reactive fibrinolysis. The patients were divided into three subgroups of 20 patients each with different intensities of oral anticoagulation as indicated by International Normalized Ratio (INR) values in the ranges 4.8-3.6, 3.5-2.5 and 2.4-2.1. From the two markers of coagulation activation studied (prothrombin fragment 1 + 2 and thrombin-antithrombin III (TAT)) the prothrombin fragment 1 + 2 was dependent on the INR level in all groups, although the median values were still significantly beneath the lower limit of the reference range. The D-dimer concentrations were unexpectedly high with respect to the low coagulation activation levels, as indicated by the D-dimer/TAT and D-dimer/F 1 + 2 ratios. This demonstrates the enhanced presence of fibrin degradation products as a scarcely described side-effect of oral anticoagulation. The anticoagulant properties of fibrin degradation products might contribute partly to the in vivo haemorrhagic risk in high-intensity oral anticoagulation. These results show, inasmuch as the prothrombin fragment 1 + 2 is concerned, that from the laboratory point of view the residual thrombin activity is low enough to be adequate under the therapeutical regimen followed in this study. However, the question of the efficacy of anticoagulation intensities can only be finally answered by clinical trials.

Administration, Oral↗
PubMed1991

Stress distribution on the cusps of a polyurethane trileaflet heart valve prosthesis in the closed position.

In this paper, a finite element analysis of the stress distribution on the cusps of a polyurethane trileaflet heart valve prosthesis in the closed position is presented. The geometry of the valve was modified from a relationship proposed by Ghista and Reul (J. Biomechanics 10, 313-324, 1977). The effects of variations in stent height, leaflet thickness and coaptation area on the stress distribution were also analyzed. Analyses were performed with both rigid and flexible stents for the trileaflet valve in order to delineate the effect of stent flexibility on the leaflet stress distribution. The results showed that regions of stress concentration were present near the commissural attachment similar to those predicted with the bioprostheses. The stresses on the leaflets were reduced by increasing the stent height with both rigid and flexible stents. Selectively increasing the leaflet thickness near the commissures and also increasing the coaptation area did not prove to reduce the leaflet stresses when the stent flexibility was taken into account. The possible effect of high stresses on the structural integrity of polyurethane leaflets and its relationship with calcification is yet to be investigated.

Heart Valve Prosthesis↗
PubMed1991

Static and dynamic stresses during valve closure of a bileaflet mechanical heart valve prosthesis.

The effect of contact geometry and component compliance on the magnitude, distribution, and state of various types of stresses on a bileaflet mechanical heart valve prosthesis during valve closure was analyzed using an Edwards-Duromedics mitral valve as example. Static and dynamic stresses developing on both the leaflet and pivot ball during valve closure were modeled using finite element analysis (FEA). Uniform contact between the leaflet and housing as well as between the pivot ball and pivot slot can significantly reduce both static and dynamic stresses around the contact area. The level of the dynamic flexural stresses can be an order of magnitude higher than that of the static stresses. When both the radial and axial compliance of the housing are taken into consideration, peak dynamic stress was more than 40% less than that generated through the impact between a moving leaflet and a non-compliant rigid housing.

Compliance↗
PubMed1979

[Sanatorium stage in the rehabilitation of patients with rheumatic defects after heart valve prosthesis].

In 93.2% of 104 patients treated at a cardiological sanatorium after heart valve prosthetics the condition had improved by the time of discharge and only in 2.9% (3 patients) it had grown worse. The measures of rehabilitation comprised curative, physical, and psychologic aspects. The improvement in the condition of patients who had been operated on was attested by the results of ECG, polycardiography, and external respiration tests. The increased tolerance to physical load and the improved ability for coping with the tasks of every-day life are also objective indicators of the effectiveness of the stage of sanatorium treatment in the general complex of rehabilitation of patients who had been subjected to heart valve prosthetics.

Adolescent↗
PubMed1979

[Heart valve prosthesis and pregnancy].

Sixteen pregnancies were followed up in 13 patients with prosthetic heart valves: 8 pregnancies went to term under oral anticoagulation, 4 under heparin and 4 without anticoagulation. 9 healthy normal children were delivered; there were 2 still births and 5 abortions. On the maternal side 3 haemorrhages and thromboembolic episodes which involved 2 patients on heparin, one of whom died, were observed. The following points are apparent from our observations and a review of the existing medical literature: --the risk of thromboembolism is not increased. The marked clotting tendency of maternal blood post-partum contraindicates the withdrawal of anticoagulants during this critical period; --haemorrhagic complications are common with anticoagulants; --foetal loss is greatly increased; --the teratogenecity of vitamin-K antagonists is certain, but the risk is small. The problems of anticoagulation are discussed; theoretically heparin should be given during the 1st trimestre and from the 38th week to the second post-partum week. The patients should be closely supervised by both obstetrician and cardiologist and hospitalisation is advised for the last month of pregnancy. Normal vaginal delivery is usually possible.

Abnormalities, Drug-Induced↗
PubMed1991

[Reoperations in patients with heart valve prosthesis].

The results of operations performed for the second time on 193 patients with heart valve prostheses are analysed. Prosthesis endocarditis and thrombosis of the prosthesis are the most severe complications of valve replacement. An effective scheme for the performance of repeated operations in these patients is suggested, which was developed at the Bakulev Institute of Cardiovascular Surgery, USSR AMS. The study makes it possible to conclude that the risk of such operations is fully justified.

Adolescent↗