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At least 433 records · Page 24Linked to original sources
PubMed1988

[Late thrombo-embolic complications after heart valve prosthesis].

A follow-up study of 444 patients with artificial heart valves of different makes demonstrated increased wear and thrombogenic properties of the hemispheric MKC-27 prosthesis, used in mitral position, over 5 years of follow-up. High risk of thrombo-embolic complications is related to interrupted anticoagulant treatment. Their rate could be reduced through improving the quality of anticoagulant treatment, i.e. continuous administration of anticoagulants under adequate monitoring.

Anticoagulants↗
PubMed1994

Hemodynamic effects and echocardiographic consequences of tension-free pericardial closure after heart valve surgery.

Pericardial closure early after open heart surgery has been shown to consistently lower cardiac output and stroke volume, while mean arterial blood pressure is maintained by an increase in systemic vascular resistance. In 10 patients (seven females) (mean age 65 +/- 4 years) undergoing an open heart valve procedure, the effects of a tension-free pericardial closure technique were studied using thermodilution studies and transesophageal echocardiography. The following variables were recorded: mean arterial pressure, mean pulmonary artery pressure, right atrial pressure, cardiac output, stroke volume, systemic vascular resistance, and systolic and diastolic left ventricular dimensions, and left ventricular wall thickness. Observations were made after the heart was decannulated, both while the pericardium was open and after it had been closed by a tension-free technique, and then after closure of the chest. Further observations were made while the chest remained closed, both before and after the pericardium had been reopened by removing the pericardial suture through the chest wall. Closing the pericardium with the tension-free technique while the chest remained open was followed by a fall in cardiac output by 8% and a 15% fall in systemic vascular resistance (both n.s.). These changes caused a 13% reduction in the mean arterial pressure (p = 0.03). Ejection fraction did not change, and systolic and diastolic left ventricular dimensions decreased by 6% and 4% respectively (both n.s.). Opening the pericardium (1.5 to 2 hours after the end of the operation) while the chest remained closed was not followed by significant change in any of the hemodynamic or echocardiographic variables.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Computer modelling of bioprosthetic heart valves.

The underlying assumptions and principles of a computer-based model for tissue heart valves are described. The model is used to relate observations of leaflet morphology to the requirements of proper valve function. Stress is the fundamental mechanical factor that limits the longevity of bioprosthetic heart valves--the higher the stress levels in the leaflets, the shorter will be the time over which the leaflets can maintain satisfactory structural integrity. Direct measurement of stress is impractical with real heart valves, but the calculation of stress and the study of its interdependence on other key parameters of tissue valve design is a good alternative. The methodology of computer modelling of heart valves is discussed and the technique is illustrated with some examples. Models of pericardial valves, the aortic allograft and porcine bioprostheses are compared.

Bioprosthesis↗
PubMed1982

The clinical life history of explanted prosthetic heart valves.

This report analyzes 118 prosthetic heart valves obtained from 97 patients at reoperation (96) or at postmortem examination (22). The number obtained from the mitral, aortic, and tricuspid positions were 78, 32, and 8, respectively. Duration of implant ranged from one day to 12.3 years. Valves showing the least long-term wear were the Starr-Edwards metal strut-silicone bell and the Björk-Shiley. Moderate long-term durability was provided by the Beall and Starr-Edwards cloth-covered composite-seat prostheses while short-term durability was given by Hancock and Carpentier valves. Reoperation for valve-related causes was performed for 46 of 47 Beall valves, which demonstrated stenosis, hemolysis, and incompetence from component wear, 6 of 27 Björk-Shiley prostheses for valve thrombosis or thromboembolism or both, and 11 of 17 porcine prostheses because of calcification (4) or cusp perforation or rupture. Analyses of wear and fatigue of mechanical valves demonstrated that use of ultrahard materials (pyrolyte carbon, titanium, stellite 21) provided superior durability in contrast to polymeric solids or fabrics with poor abrasion and impact characteristics. Further, cloth and disc wear were evident as early as 0.5 year after implant and appeared to be complete by 4 years. Completeness of healing after 24 months was not related to the type of fabric material used or its construction. This study suggests that mechanical valves made from hard materials have long durability when properly implanted and require fastidious prophylaxis against infection and thromboembolism. The findings of early cusp perforation or rupture in the aortic position and leaflet calcification, stiffening, or disruption in the mitral position for porcine prostheses suggest that frequent and careful examinations of patients with these prostheses are required to detect early signs of stenosis or incompetence and that early reoperation is required before catastrophic valve failure necessitates emergency prosthetic valve replacement.

Aortic Valve↗
PubMed2005

Heart valve tissue engineering.

Tissue-engineered heart valves have been proposed by physicians and scientists alike to be the ultimate solution for treating valvular heart disease. Rather than replacing a diseased or defective native valve with a mechanical or animal tissue-derived artificial valve, a tissue-engineered valve would be a living organ, able to respond to growth and physiological forces in the same way that the native aortic valve does. Two main approaches have been attempted over the past 10 to 15 years: regeneration and repopulation. Regeneration involves the implantation of a resorbable matrix that is expected to remodel in vivo and yield a functional valve composed of the cells and connective tissue proteins of the patient. Repopulation involves implanting a whole porcine aortic valve that has been previously cleaned of all pig cells, leaving an intact, mechanically sound connective tissue matrix. The cells of the patients are expected to repopulate and revitalize the acellular matrix, creating living tissue that already has the complex microstructure necessary for proper function and durability. Regrettably, neither of the 2 approaches has fared well in animal experiments, and the only clinical experience with tissue-engineered valves resulted in a number of early failures and patient death. This article reviews the technological details of the 2 main approaches, their rationale, their strengths and weaknesses, and the likely mechanisms for their failure. Alternative approaches to valvular tissue engineering, as well as the role of industry in shaping this field in the future, are also reviewed.

Animals↗
PubMed1994

In vitro fluid dynamic evaluation of the Carbomedics bileaflet heart valve prosthesis in the aortic and mitral positions.

Since the introduction of bileaflet heart valve prostheses their clinical use has continued to escalate. The first of this valve type was the Standard St. Jude Medical (SSJM) prosthetic heart valve in 1977. The Carbomedics prosthetic heart valve (CPHV), introduced in the late 1980s, was intended to improve on the design of the SSJM bileaflet valve. The design changes in the CPHV valve, relative to the SSJM valve, may have the potential to affect its flow fields. This study, using flow visualization laser Doppler velocity measurements and color Doppler flow mapping, was intended to evaluate how these changes affect the flow fields in the near vicinity of the CPHV valve. The study was conducted in an in vitro pulse duplicator system. In the flow visualization study, the flow fields observed with the CPHV valve were quantitatively similar to those seen with the SSJM valve. Centralized jet-like flows with flow separation/stagnation were observed in the illuminated planes. The jet-like flows from the two lateral orifices were broader than that observed from the central orifice for both the CPHV and the SSJM valves. This fact implied that the major part of the volumetric flow was through the two lateral orifices, rather than the central orifice. In the laser Doppler velocity measurements, it was found that the flow field downstream of the SSJM valve was slightly more evenly distributed than that with the CPHV valve. In addition, the extent of the flow separation regions with the CPHV valve were slightly larger than with the SSJM valve. The slight differences in velocity profiles between the SSJM and the CPHV valves were due to the differences in leaflet opening angle. However, the levels of flow turbulence with the CPHV and the SSJM valves were found to be of the same order of magnitude. The results of the flow visualization and LDA velocity and turbulence measurements obtained in the study indicate that the differences in flow fields in the immediate vicinity of the CPHV valve relative to the SSJM valve are insignificant.

Aortic Valve↗
PubMed1981

Creep and flexibility measurements on plastic frames for tissue heart valves.

Measurements on plastic flexible frames for heart valves have shown that the design influences the creep potential of any one plastic material. This has been shown for both in vitro accelerated fatigue tests and after clinical implantation of more than 10 years. The flexibility of the plastic, a polypropylene, was not affected either by fatigue testing, shelf storage or clinical implantation. The possibility of 30 years freedom from creep for a flexible plastic frame for a tissue heart valve has been examined.

Heart Valve Prosthesis↗
PubMed1992

Experimental evaluation of an autologous tissue heart valve.

The goal of the autologous tissue heart valve (ATHV) prosthesis project has been the development of a non-antigenic, non-calcifying bioprosthesis of greater durability than heterograft or homograft bioprostheses. It is made in the operating room, at a sterile work bench, during surgery for heart valve replacement. Autologous pericardium is used for valve construction after a five minute immersion in 0.6 per cent glutaraldehyde buffered to pH 7.4 with phosphate. The stent-mounted trileaflet prosthesis can be made in five minutes with a semi-automated method that uses two concentric mating stents that substitute clamping for sewing of the tissue. In vitro testing, to include pulse duplicator, accelerated wear tester, static testing for leakage and tensile strength testing, has been performed with ATHVs made with glutaraldehyde-tanned bovine and ovine pericardium. Transvalvular pressure gradients were measured at 3.3-7.3 mmHg at flow rates of 4-5 l/min. Six valves have been tested beyond 800,000,000 cycles with full opening and closing at differential closing pressures of 125 mmHg. One of the valves developed a 2mm leaflet tear after 26,000,000 cycles but the remaining five survived intact. No fractures were seen in the Dacron covered Delrin stents. Six ATHVs were implanted in juvenile sheep for five months. One animal died after five months of infective endocarditis secondary to an unrecognized deep wound infection and the other five were electively sacrificed at the same time interval. Four valves were fully competent at terminal elective cardiac catheterization and one showed minimal insufficiency attributed to a paravalvular leak. The leaflet tissue was free of generalized calcification in all instances. There was no evidence of leaflet tissue thickening or shrinkage. The mean calcium content at necropsy of the 15 leaflets from the five valves was 8.357 mg/g of tissue. There is experimental evidence that an ATHV made of pericardium treated briefly with glutaraldehyde may achieve the goal of a non-calcifying, more durable bioprosthesis.

Animals↗
PubMed2000

The quality of heart valve tissue for homograft transplantation.

BACKGROUND AND AIM OF THE STUDY: The results of heart valve replacement surgery may be improved by refining surgical techniques and/or developing new heart valve transplants. The aim of this study was to examine the effect of age on the presence of cholesterol clefts and lipid deposits in the cusp base and sinus wall of aortic homografts. METHODS: Seventy-one valves were obtained at autopsy from donors (aged 15- 40 years) with no history of illness or evidence of serious illness. Trauma was the predominant cause of death among patients. The valves were examined using an osmium-vaporization technique. RESULTS: Osmiophilic deposits were detected in the cusp base in 28 cases (42%), and in the sinus wall in 49 cases (69%). Cholesterol crystals in the cusp base were found in 16 cases (24%), and sinus wall cholesterol clefts in 26 cases (38%). The model-predicted probability of cusp base lipid deposits existing was 76% in 40-year-old donors, 36% in 30-years-olds, and 11% in 20-year-olds; the probability of cusp base cholesterol clefts existing was 45%, 21% and 8% in these age groups, respectively. The influences of immunological reactions, biochemical changes (centers of calcification) and acceleration of atherosclerotic processes are discussed. CONCLUSION: The microscopic study of heart valves demonstrated the presence of lipid deposits in subjects of an unexpectedly young age. Among our study material, 58% of valves obtained from donors aged 11-40 years were unsuitable for transplantation. Our results confirmed the need for macroscopic inspection of heart valves before their being transplanted.

Adolescent↗
PubMed1994

[Operative strategy for redo heart valve operation].

Thirty-five redo heart valve operations were performed between Jan. 1990 and Dec. 1993 in Jichi Ohmiya Medical Center. Previous operations were mitral valve replacement (MVR) in 19, closed mitral commissurotomy in 1, open mitral commissurotomy in 6, aortic valve replacement (AVR) in 5, ASD repair in 3, VSD repair in 1. Thirty (85.7%) were in NYHA functional class III or less, and 5 (14.3%) were in functional class in IV. Twenty-three patients had undergone MVR, 5 AVR, 4 MVR+AVR, 2 TVR (TAP), 1 Cabrol operation, and 8 patients had undergone concomitant tricuspid valve repair. Emergent operation was none. Overall operative mortality was 5.7% (2/35), as the cause of death was low output syndrome. Chest CT was available for the evaluation of the distension of right atrium and right ventricle. Catastrophic hemorrhage by the injury of ascending aorta or right atrium during redo sternotomy was 4, but that was not the cause of death. We emphasize the necessity of the exposure of the femoral artery and the preparation for cardiopulmonary bypass before sternotomy. The extent of dissecting adhesion should be determined case by case respectively under consideration of the risk of cardiovascular injury and postoperative large bleeding. Furthermore the cannule of SVC or IVC with cuff was useful for the cases with strong adhesion.

Adult↗
PubMed1980

Microcalorimetric measurements of heat production in platelets of patients with prosthetic heart valves.

The heat production in resting platelets of 12 patients with prosthetic heart valves was found to be significantly decreased (p less than 0.005), P = 49 +/- 9 fW/cell. In a matched control group of eight patients with heart valve disease, the corresponding heat production value in resting platelets was P = 65 +/- 11 fW/cell. The present results indicate that the overall metabolic activity in platelets of patients with prosthetic heart valves is abnormally low.

Adult↗
PubMed2002

Translational and rotational forces on heart valve prostheses subjected ex vivo to a 4.7-T MR system.

PURPOSE: To assess the magnetic field interactions on 60 heart valve prostheses subjected to a 4.7 T MR system. It addresses the question of whether heart valves deemed safe at 1.5 T may pose safety hazards as patients are exposed to increased static magnetic fields. MATERIALS AND METHODS: Ex vivo testing was performed to evaluate translational and rotational forces on 60 heart valves using previously described techniques. RESULTS: Translational forces were detected on 58 heart valves ranging from 0.5 degrees to 7.5 degrees. Seven valves exhibited paramagnetic/weakly ferromagnetic behavior, and 51 valves exhibited diamagnetic behavior. Rotational forces were observed for 46 valves. CONCLUSIONS: Criteria previously used for safety assessment of heart valve prostheses and expressed in terms of magnetic forces suggest the forces observed in this study are compatible with the safe use of these valves in magnetic resonance (MR) systems with static fields up to 4.7 T.

Heart Valve Prosthesis↗
PubMed2001

Increased numbers of circulating donor-specific T helper lymphocytes after human heart valve transplantation.

Implantation of cryopreserved human donor heart valves for either congenital or acquired cardiac disease has been performed since the last three decades. Although the clinical outcome is good, long-term valve degeneration resulting in dysfunction has been observed. A specific immunological response of the recipient against the allograft has been proposed as one of the factors involved in this process. Helper T lymphocytes play an important intermediate role in cellular and humoral immune response. Increasing numbers of circulating donor-specific helper T lymphocytes precursors (HTLp) correlate with graft rejection after organ transplantation. To investigate whether cryopreserved human donor heart valves are able to induce a donor-specific T helper response, we monitored the HTLp frequencies (HTLpf) in peripheral blood samples of 13 patients after valve allograft transplantation by use of a limiting dilution assay followed by an interleukin-2 bioassay. Prior to transplantation, HTLpf specific for donor and third-party antigens showed individual baseline levels. After allografting, the antidonor frequencies significantly increased in 11 of the 13 patients (P = 0.02). This was not found for stimulation with third-party spleen cells (P = 0.68), which indicates a donor-specific response. Maximal donor-specific HTLpf were already found at 1--2 months after operation. Valve allograft transplantation induces an increase in the numbers of donor-specific HTLp in peripheral blood of the patients. Analogous to organ transplantation, these HTLp may play a crucial role in events that lead to valve damage. Therefore, monitoring of HTLp in peripheral blood samples might be informative for donor valve degeneration (rejection) and subsequently valve allograft failure.

Adult↗
PubMed2005

Biocompatibility and recellularization potential of an acellular porcine heart valve matrix.

BACKGROUND AND AIM OF THE STUDY: Tissue-engineered heart valves have the potential to overcome the limitations of present heart valve replacements. The study aim was to investigate the biocompatibility and recellularization potential of an acellular porcine valve matrix. METHODS: Acellular porcine valve matrix contact and extract cytotoxicity was tested against porcine fibroblasts and smooth muscle cells (SMC). Porcine cells were incubated with decellularized aortic valve leaflets and aortic wall, and then assessed for changes in morphology and contact inhibition of growth. Soluble tissue extracts were prepared from decellularized leaflets and aortic wall, and assessed for their effect on the viability of cultured porcine cells. Acellular leaflets were seeded with either fibroblasts or SMC at 1 x 10(3) to 1 x 10(6) cells/cm2 for 24 h, or 5 x 10(4) cells/cm2 for 1-4 weeks. Cell attachment onto, and migration into, the acellular matrix was assessed by scanning electron microscopy and histology. RESULTS: No contact inhibition of growth, or changes in fibroblast or SMC morphology, were observed following contact with the acellular valve matrix. No soluble extract cytotoxicity was found. Intermediate cell-seeding densities (2.5 x 10(4) to 7.5 x 10(4) cells/cm2) of both cell types produced confluent cell attachment; at the lowest concentration (1 x 10(3) cells/cm2) cell attachment was sparse, and at the highest (1 x 10(6) cells/cm2) it was multilayered. The SMC migrated throughout the leaflet matrix over four weeks, but there was no fibroblast migration into the matrix. CONCLUSION: The absence of contact and extract cytotoxicity indicated that the acellular valve matrix was biocompatible in vitro. The failure of porcine fibroblasts to grow on, or infiltrate into, the matrix suggested that the SMC may be the preferred cell type for future leaflet recellularization studies in the development of a tissue-engineered heart valve replacement.

Animals↗
PubMed1992

Failure of high-dose heparin to prevent recurrent cardioembolic strokes in a pregnant patient with a mechanical heart valve.

A 27-year-old woman with a mechanical heart valve suffered multiple thromboembolic events while pregnant despite anticoagulation with high-dose heparin. Warfarin, the anti-coagulant of choice for patients with prosthetic heart valves, is teratogenic and can cause hemorrhagic complications at delivery. Heparin reduces thromboembolic complications, but is of uncertain efficacy. We discuss alternatives for the prevention of thromboembolic complications in pregnant women with mechanical heart valves.

Adult↗
PubMed1995

Classification of prosthetic heart valve sounds: a parametric approach.

People with heart problems have had their lives extended considerably with the development of the prosthetic heart valve. Great strides have been made in the development of the valves through the use of improved materials as well as efficient mechanical designs. However, since the valves operate continuously over a long period, structural failures can occur--even though they are relatively uncommon. Here the development of techniques to classify the valve either as having intact struts or as having a separated strut, commonly called single leg separation, is discussed. In this paper the signal processing techniques employed to extract the required signals/parameters are briefly reviewed and then it is shown how they can be used to simulate a synthetic heart valve database for eventual Monte Carlo testing. Next, the optimal classifier is developed under assumed conditions and its performance is compared to that of an adaptive-type classifier implemented with a probabilistic neural network. Finally, the adaptive classifier is applied to a data set and its performance is analyzed. Based on synthetic data it is shown that excellent performance of the classifiers can be achieved implying a potentially robust solution to this classification problem.

Acoustics↗
PubMed1997

Outcome of patients treated with a St. Jude prosthetic heart valve.

BACKGROUND: Long-term outcome of patients treated with a St. Jude prosthetic heart valve was reported by investigators in Lausanne, Switzerland. This article quantifies the mortality and morbidity implications of single or multiple heart valve replacement. RESULTS: After hospital discharge, mortality ratios were highest for duration 5-10 years, roughly comparable in patients who received a single valve, and generally higher in those who received both an aortic and a mitral valve prosthesis. Outcome varied with preoperative myocardial function, but there was no survival difference among subjects with a history of stenotic, regurgitant, or mixed lesions. Postoperative complications included embolism, anticoagulant-related hemorrhage, stroke, prosthesis thrombosis, endocarditis, prosthesis dysfunction, hemolytic anemia, and reoperation. CONCLUSIONS: This study indicated that overall mortality experience was fairly comparable in patients who received a single St. Jude prosthetic heart valve and less favorable in those who received multiple valves. Long-term morbidity rates following insertion of a St. Jude prosthetic heart valve were high.

Female↗
PubMed1983

[Sound spectrographic studies in the diagnosis of dysfunctions of mechanical heart valve prostheses (Björk-Shiley prostheses)].

A newly developed real-time sound spectroanalyzer was found to be capable of diagnosing malfunction of prosthetic heart valves (Björk-Shiley prostheses). Sound spectroanalysis was carried out 430 times on 257 patients with a prosthetic heart valve. The valvular click of prosthetic heart valves shows a typical sound spectroanalysis pattern in real time, with a high-frequency peak which diminishes beyond 25 kHz. Thrombosis of the prosthetic heart valve causes loss of the valvular click and reduction in the intensity of the high-frequency components, as shown in 4 patients. Thus the sound spectroanalysis appears to be a noninvasive technique which may allow early diagnosis of a thrombosed prosthetic heart valve. We believe this method to be superior to phonocardiography and echocardiography.

Aortic Valve↗