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PubMed2005

A comparison of flow field structures of two tri-leaflet polymeric heart valves.

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 in vitro study, the velocity fields inside and downstream of two different prototype tri-lealfet polymeric heart valves were studied. Experiments were conducted on two 23 mm prototype polymeric valves, provided by AorTech Europe, having open or closed commissure designs and leaflet thickness of 120 and 80 microm, respectively. A two-dimensional LDV system was used to measure the velocity fields in the vicinity of the two valves under simulated physiological conditions. Both commissural design and leaflet thickness were found to affect the flow characteristics. In particular, very high levels of Reynolds shear stress of 13,000 dynes/cm2 were found in the leakage flow of the open commisure design. Maximum leakage velocities in the open and closed designs were 3.6 m/s and 0.5 m/s respectively; the peak forward flow velocities were 2.0 m/s and 2.6 m/s, respectively. In both valve designs, shear stress levels exceeding 4,000 dyne/cm2 were observed at the trailing edge of the leaflets and in the leakage and central orifice jets during peak systole. Additionally, regions of low velocity flow conducive to thrombus formation were observed in diastole. The flow structures measured in these experiments are consistent with the location of thrombus formation observed in preliminary animal experiments.

Animals↗
PubMed2003

Role of elastin in pathologic calcification of xenograft heart valves.

Bioprosthetic heart valves fabricated from glutaraldehyde crosslinked porcine aortic valves often fail because of calcific degeneration. Calcification occurs in both cusp and aortic wall portions of bioprosthetic heart valves. The purpose of this study was to discern the role of different aortic wall components in the calcification process. Thus, we selectively extracted cells and other extracellular matrix proteins from porcine aorta using trypsin/DNase/RNase, cyanogen bromide (CNBr), and sodium hydroxide (NaOH) treatments and subdermally implanted these pretreated aortas in young rats. Total DNA and phospholipid data showed complete removal of cells by CNBr and NaOH treatments, whereas trypsin/DNase/RNase treatment was effective in removing DNA but not phospholipids. As shown by amino acid data and Masson's trichrome staining, collagen was removed in CNBr and NaOH treatments. Control fresh porcine aorta calcified significantly after 21 days of implantation (Ca 26.4 +/- 2.4 microg/mg). Removal of cells and collagen from the aorta by CNBr treatment did not lead to a statistically significant reduction in aortic calcification (Ca 20.8 +/- 3.0 microg/mg). Moreover, partial degradation of elastin fibers caused by NaOH (during extraction) and trypsin treatment (after implantation) of the aorta significantly increased elastin-oriented calcification (Ca 94.4 +/- 9.3 and 58.4 +/- 4.6 microg/mg, respectively). Our results indicate that the elastin component of the aorta may undergo independent calcification irrespective of devitalized cell-mediated calcification observed in glutaraldehyde crosslinked aortas. Our results also demonstrate the importance of studying elastin-oriented calcification in decellularized elastin-rich aortic matrices currently used in tissue-engineering applications.

Amino Acids↗
PubMed1986

[Long-term studies following heart valve replacement].

Heart valve replacement has become a routine procedure in the treatment of patients suffering from valvular lesions. The results of long-term follow-up studies after valve replacement are still important and help to choose the optimal time for surgical intervention and the type of prosthesis. In order to ensure comparability of publications a consent must be found with regard to the demands these publications should fulfill concerning the selection and presentation of data. Generally, retrospective analyses are inappropriate to prove the influence of preoperative or perioperative parameters (e.g. the type of prosthesis) on the late outcome. They may be useful for raising hypotheses. Survival or event-free rates can only be determined reproducibly if adequate follow-up methods are used. By questionnaires at long time intervals important informations are often lost. The duration of the follow-up period depends on whether the event in question occurs with a constant incidence (e.g. bleeding complications due to anticoagulant therapy) or has an inconstant hazard-rate (e.g. primary failure of tissue valves). Increasing hazard-rates in the late postoperative course necessitate adequate follow-up periods. The number of patients followed up has to be determined prospectively so that differences between patient groups may be sufficiently proven after an adequate follow-up period.

Follow-Up Studies↗
PubMed1993

Utilization of manufacturers' implant card data to estimate heart valve failure.

Heart valve manufacturers possess the most complete inventory of world-wide mechanical valve failures, but to convert failures to time-related risks requires estimates of patient follow up. Since manufacturers did not actively track patients, they needed a model that incorporates an assumed death rate to decrease the numbers of patients at risk. We present a method for using a manufacturer's implant card database to estimate time-related complication rates for patient subsets, and illustrate its use by examining the risk of outlet strut fracture (OSF) with the Björk-Shiley 60 degrees Convexo-Concave valve (CC60). We developed a parametric model for valve patient survival based on actively followed valve patients from three centers using only variables typically available from implant cards. Using this survival model, a simulated lifetime was produced for each valve in the CC60 implant database for which the required covariates were known. These lifetimes were then used to analyze OSF as if they were true follow up times. This allowed the use of conventional methods of univariate and multivariate analysis for OSF, including parametric statistical models. According to the approximate linearity of the cumulative hazard functions, OSF risk over time appeared to be fairly constant. Several risk factors were identified, including valve size, patient age at implant and valve position. Using parametric models for both patient survival and OSF permits the estimation of the probability of OSF before death for an individual patient (as opposed to the usual actuarial probability of OSF given that the patient does not die). Because the patient may die before his valve would have failed, this cumulative incidence of OSF is always less than the actuarial risk. For all but the very highest risk patients, the cumulative incidence over their relatively short remaining lifetimes is very small.

Actuarial Analysis↗
PubMedDate not supplied

Biological heart valve--an alternative to mechanical valve.

Bioprosthetic heart valve, derived from human or animal tissues is a commercial, implantable valve characterised by good haemodynamic parameters, low haemolysis ratio and satisfactory durability. Until now, its wide-spread therapeutic use has been limited by the progressing leaflet calcification. The aim of the paper is to present the benefits, adverse reactions as well as problems associated with the improvement of this bioprosthesis.

Animals↗
PubMedDate not supplied

Tissue engineering of heart valves: formation of a three-dimensional tissue using porcine heart valve cells.

Tissue engineering is a promising approach to obtaining lifetime durability of heart valves. The goal of this study was to develop a heart valve-like tissue and to compare the ultrastructure with normal valves. Myofibroblasts and endothelial cells were seeded on a type I collagen scaffold. The histologic organization and extracellular matrix were compared in light and electron micrographs. Radiolabeled proteoglycans were characterized by enzymatic degradation experiments. In tissue engineered specimens, cross sectional evaluation revealed that the scaffold (300 microm) was consistently infiltrated with myofibroblasts. Both sides were covered with a multicellular layer of myofibroblasts and overlaid by endothelial cells (50 microm). A newly formed extracellular matrix containing collagen fibrils and proteoglycans was found in the interstitial space. Collagen fibrils with a 60 nm banding pattern were found in both specimens. Small sized proteoglycans (65 nm) were associated and aligned at intervals of 60 nm with collagen fibrils. Large sized proteoglycans (180 nm) were located outside the collagen bundles in amorphous compartments of the extracellular matrix. The majority of glycosaminoglycans were chondroitin/dermatan sulfate, and a minority were heparan sulfate. The morphology and topography of cells and the organization of extracellular matrix in artificial tissues strongly resembles those of native valve tissues.

Animals↗
PubMed1993

Catheter-implanted prosthetic heart valves. Transluminal catheter implantation of a new expandable artificial heart valve in the descending thoracic aorta in isolated vessels and closed chest pigs.

A new expandable artificial heart valve was developed for implantation by a transluminal catheter technique without using thoracotomy or extracorporeal circulation. The aim of this study was to implant the valve in isolated vessels of the descending thoracic aorta as well as in closed chest pigs, and furthermore to study the prosthesis' mechanical stability and the valve function. The artificial valve was made by mounting a porcine aortic valve on an expandable stent. Before implantation, the stent-valve was compressed on a deflated balloon catheter and mounted inside an introducer sheath. After intravascular introduction to the descending thoracic aorta the stent-valve was discharged from the sheath. Implantation was performed by balloon inflation which expanded the stent-valve to a diameter exceeding the internal vessel's diameter. After balloon deflation the stent-valve maintained an expanded configuration ensuring a stable fixation against the vessel wall. In vitro implantations were performed in 36 isolated descending thoracic aorta specimens obtained from 80 kg pigs. Mechanical stability was evaluated by applying a downing load to the prosthesis. No displacement occurred at loads < or = 1 kg when a large balloon (31 mm) was used for implantation. Transvalvular pressure differences between 11-47 mmHg (median) were obtained at antegrade flowrates between 5-8 l/min. Furthermore, only moderate leakage flows were measured during retrograde perfusion. In vivo implantations were performed in six 80 kg pigs. Implantation was safe and easy, and angiograph and haemodynamic evaluations revealed essentially no stenosis or regurgitation. No complications in migration, perforation, hemorrhage or thrombosis were observed. This study indicates a good mechanical stability and valve function of the new expandable artificial valves.

Animals↗
PubMed1988

Retraction of bioprosthetic heart valve cusps: a cause of wide-open regurgitation in right-sided heart valves.

Most failures of bioprosthetic heart valves in children are due to stenosis secondary to thrombus, calcific deposits, or tissue ingrowth. Valve failures due to regurgitation typically involve cuspal detachment, tears, or perforations. We present four cases of prosthetic valve regurgitation in children caused by cuspal retraction without stenosis and describe the morphologic findings related to the valves at autopsy or explantation. A mononuclear cell and giant cell response to the cusps of the valve was a striking finding in one patient.

Adolescent↗
PubMed2001

[Patient-adapted valve selection: biological vs. mechanical heart valve replacement in aortic valve diseases].

Since the first aortic valve replacement performed by Harken in 1960, the operation of aortic valve disease by replacing the native valve with a heart valve prosthesis has become one of the most frequently performed procedures in cardiac surgery. For valve replacement there are biological (xenografts and homografts) and mechanical heart valve prostheses available. When choosing the most suitable prosthesis the limited durability of a biological prosthesis and the risks of lifelong anticoagulation for a mechanical prosthesis have to be balanced. In this article the indication for operation of aortic valve stenosis and aortic regurgitation are discussed first. Based on the literature of the last 2 years the advantages and disadvantages of mechanical and biological heart valve prostheses (xenograft, homograft and ROSS procedure) are discussed. In addition rarely used techniques like aortic valve reconstruction are presented. Due to the fact that a biological prosthesis has a durability of 12-15 years and the risk of bleeding complications under anticoagulation grows with increasing age, the choice of a biological prosthesis can be recommended from the age of 65 years. Results of long-term studies at to whether this limit can be diminished by using a stentless biological prosthesis have to be awaited.

Aged↗