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PubMed2003

Cardiac rehabilitation following percutaneous revascularization, heart transplant, heart valve surgery, and for chronic heart failure.

This review discusses the scientific and clinical evidence for cardiac rehabilitation in patients who have undergone percutaneous revascularization, heart transplant, and heart valve surgery, and in patients with chronic heart failure. Across these diagnoses, regardless of age, there is considerable benefit of cardiac rehabilitation and supervised exercise training for increasing functional capacity, favorably modifying disease-related risk factors, decreasing symptoms, detecting signs and symptoms of disease before they become serious complications, and improving quality of life. The available evidence for this component of cardiovascular disease management, albeit not perfect, still warrants its more widespread application.

Angioplasty, Balloon, Coronary↗
PubMed1993

Prediction of valve-related complications for artificial heart valves using adaptive neural networks: a preliminary study.

A novel approach to the prediction of valve-related complications in patients with implanted artificial heart valves is discussed. Adaptive artificial neural networks were used to identify patients at high risk of valve-related events based on preoperative data. Data from a clinical trial on 789 subjects with Carpentier-Edwards pericardial bioprostheses were used. Patients' records were divided into two groups, one of which was used for training the neural network and the other for testing the trained network and determining error rates. Patient information such as age, sex, NYHA class and anticoagulation therapy, as well as valve information such as size and the date of implant, were used as the network inputs. The neural net had a single output variable indicating the risk that an individual patient would develop a valve-related complication resulting in death. The results show that a trained neural network was able to predict valve-related deaths in the specified time interval of 1981-1991 with a high degree of accuracy. The neural network was also successful in classifying patients into high and low risk categories.

Animals↗
PubMed1982

Rate of methicillin penetration into normal heart valve and experimental endocarditis lesions.

Methicillin concentrations were measured in serum, normal heart valves, damaged heart valves, myocardium, and extravascular fluid from 12 New Zealand white rabbits to assess the influence of valvular damage on methicillin penetrations. Fibrin scarring of the aortic valve was induced by the placement of a polyethylene catheter through the aortic leaflet for 4 days. Each rabbit was then given a 40-mg/kg intravenous bolus dose of methicillin. Serum concentrations were collected, and animals were sacrificed 5, 15, 30, and 60 min after the dose. Normal and damaged heart valves from six different rabbits were desiccated to evaluate the fluid content of each. The time course of methicillin in damaged aortic valves was similar to that in serum and followed a bioexponential decline. The pharmacokinetic profile of methicillin in normal heart muscle and normal heart valves was clearly different from that of serum and damaged heart valves. Damaged valves showed a rapid and complete equilibrium with serum, whereas normal heart valve and muscle methicillin concentrations were consistently lower than serum concentrations at all times after the rapid bolus dose. The greater extravascular fluid content in damaged heart valves (P less than 0.001) compared with that in normal heart valves may be associated with the greater extent of penetration into damaged heart valves. Equilibrium between serum and damaged valves may be achieved more rapidly because the damaged area is composed of platelet and fibrin matrix and lacks the membrane integrity of normal heart valve tissue.

Animals↗
PubMed2004

Anticoagulation in pregnant women with prosthetic heart valves.

The combination of heart disease and pregnancy can present a formidable challenge to the clinician entrusted to care for both the mother and fetus. Since most data is retrospective, a definitive prognosis for such a patient may be difficult to obtain. Nevertheless, certain cardiac conditions carry greater risks of maternal mortality than do others. However, even for certain preexisting conditions, a tremendous amount of debate persists with respect to risks during pregnancy and optimal peripartum management. One such area of controversy concerns anticoagulation in pregnant women with prosthetic heart valves. For patients who require anticoagulation for mechanical valves, the choice of some combination of warfarin, unfractionated heparin, and low-molecular-weight heparin (LMWH) has resulted in many small-scale trials, which have not yet provided definite guidance as to the best course of action. Even more controversial has been the recent labeling change that advises against the use of LMWH in all patients with prosthetic heart valves, as a result of two cases of prosthetic valve thrombosis in women using LMWH while pregnant. Although the latest product labeling, in the summer of 2003, was changed to a less restrictive recommendation, debate persists. A discussion of the available data on anticoagulation in pregnant women with prosthetic heart valves is presented here, to inform the clinician and the patient of the risks and benefits of the options presently available.

Anticoagulants↗
PubMed2004

Review article: Tissue engineering of semilunar heart valves: current status and future developments.

Heart valve replacement represents the most common surgical therapy for end-stage valvular heart diseases. One major drawback that all heart valve replacements have in common is the lack of growth, repair, and remodeling capability once implanted into the body. The emerging field of tissue engineering is focusing on the in-vitro generation of functional, living semilunar heart valve replacements. This review presents a state-of-the-art overview of the physiological and biomechanical requirements of semilunar heart valves, focusing on the aortic valve. Moreover, recent heart valve tissue engineering is summarized and future options and improvements on the way towards clinical applications are discussed.

Animals↗
PubMed1992

Analysis of regurgitant jets in natural and bio-prosthetic heart valves.

Artificial bio-prosthetic heart valves are prone to fatigue tearing, having a 50% failure rate in ten years. Tears in valves give rise to pulsing reverse flow back through the valve. This is termed regurgitant flow and the resultant jet of blood a regurgitant jet. The regurgitant volume of the jet during the pulsing cycle gives a measure of the severity of the valve defect and clinical significance. Hence, it is important for the cardiologists to be able to quantify this volume. Although the velocity of the regurgitant jet can be determined using Doppler ultrasound, the dimensions of the heart valve lesion cannot be measured directly; hence, the volumetric flow rate cannot be quantified accurately. At present the severity of the regurgitant jet is assessed qualitatively from the intrusion of the jet into the cardiac chamber. In the present study, classical mathematical theories of turbulent jets have been used to describe the velocity distributions for the types of jets expected in defective heart valves and these distributions have been verified experimentally. One of these models has been developed to enable the regurgitant volumetric flow through an axisymmetric orifice of unknown radius to be calculated from the velocity distribution of the jet. This relationship may be used in conjunction with ultrasound techniques to quantify the regurgitant volume within defective artificial heart valve implants. The present study shows that there is a significant difference in the velocity distributions in jets emanating from axisymmetric and high aspect ratio slots.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioprosthesis↗
PubMed2004

Design and manufacture of a polyvinyl alcohol (PVA) cryogel tri-leaflet heart valve prosthesis.

Although current artificial heart valves are life sustaining medical devices, improvements are still necessary to address deficiencies. Bioprosthetic valves have a compromised fatigue life, while mechanical valves have better durability but are prone to thromboembolic complications. A novel, one-piece, tricuspid valve, consisting of leaflets, stent and sewing ring, made entirely from the hydrogel, polyvinyl alcohol cryogel (PVA-C), has been developed and demonstrated. This valve has three thin leaflets attached to a cylindrical stent. In order to approximate the complex shape of the surface of the natural heart valve leaflets, two different geometries have been proposed: revolution about an axis of a hyperboloid shape and revolution about an axis of an arc subtending (joining) two straight lines. The parameters of both geometries were examined based on a compromise between avoiding sharp curvature of leaflets and minimization of the central opening of the valve when closed. The revolution of an arc subtending two straight lines was selected as the preferred geometry since it has the benefit of a smaller central opening when the value of the maximum curvature for the leaflets is the same for each valve geometry. A cavity mold has been designed and constructed to form the PVA-C heart valve. The three leaflets were formed and integrated into the stent and sewing ring in a single process. Prototype heart valves were manufactured in the mold from a solution of PVA and water, by controlled freezing and thawing cycles.

Animals↗
PubMed2005

Lactatdehydrogenase (LDH) prior and post implantation of ATS heart valves.

Establishing guidelines towards an assessment of prostheses dysfunction using LDH as a marker is difficult as shown by [M. Suedkamp, A.J. Lercher, F. Mueller-Riemenschneider, K. LaRosee, P. Tossios, U. Mehlhorn, Hemolysis parameters of St Jude Medical hemodynamic valves in aortic position, Int. J. Cardiol (95) (2004) 89-93]. In response to their work we would like to add our data concerning ATS valves (AP) and say a word of caution in interpreting an increase of LDH values.

Aortic Valve↗
PubMed1997

Effects of tilting disk heart valve gap width on regurgitant flow through an artificial heart mitral valve.

While many investigators have measured the turbulent stresses associated with forward flow through tilting disk heart valves, only recently has attention been given to the regurgitant jets formed as fluid is squeezed through the gap between the occluder and housing of a closed valve. The objective of this investigation was to determine the effect of gap width on the turbulent stresses of the regurgitant jets through a Björk-Shiley monostrut tilting disk heart valve seated in the mitral position of a Penn State artificial heart. A 2 component laser-Doppler velocimetry system with a temporal resolution of 1 ms was used to measure the instantaneous velocities in the regurgitant jets in the major and minor orifices around the mitral valve. The gap width was controlled through temperature variation by taking advantage of the large difference between the thermal expansion coefficients of the Delrin occluder and the Stellite housing of Björk-Shiley monostrut valves. The turbulent shear stress and mean (ensemble averaged) velocity were incorporated into a model of red blood cell damage to assess the potential for hemolytic damage at each gap width investigated. The results revealed that the minor orifice tends to form stronger jets during regurgitant flow than the major orifice, indicating that the gap width is not uniform around the circumference of the valve. Based on the results of a red blood cell damage model, the hemolytic potential of the mitral valve decreases as the gap width increases. This investigation also established that the hemolytic potential of the regurgitant phase of valve operation is comparable to, if not greater than, the hemolytic potential of forward flow, consistent with experimental data on hemolysis.

Blood Flow Velocity↗
PubMed1978

Characterization of pepsin-solubilized bovine heart-valve collagen.

Collagens extracted from heart valves by using limited pepsin digestion were fractionated by differential salt precipitation. Collagen types were identified by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, amino acid analysis and cleavage with CNBr. Heart-valve collagen was heterogeneous in nature, consisting of a mixture of type-I and type-III collagens. The identity of type-III collagen was established on the basis of (a) insolubility in 1.7 M-NaC1 at neutral pH, (b) behaviour of this collagen fraction on gel electrophoresis under reducing and non-reducing conditions, (c) amino acid analysis showing a hydroxyproline/proline ratio greater than 1, and (d) profile of CNBr peptides on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis showing a peak characteristic for type-III collagen containing peptides alpha1(III)CB8 and alpha1(III)CB3. In addition to types-I and -III collagen, a collagen polypeptide not previously described in heart valves was identified. This polypeptide represented approx. 30% of the collagen fraction precipitated at 4.0 M-NaCl, it migrated between beta- and alpha1-collagen chains on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and its electrophoretic behaviour was not affected by disulphide-bond reduction. All collagen fractions from the heart valves contained increased amounts of hydroxylysine when compared with type-I and -III collagens from other tissues. The presence of beta- and gamma-chains and higher aggregates in pepsin-solubilized collagen indicated that these collagens were highly cross-linked and suggested that some of these cross-links involved the triple-helical regions of the molecule. It is likely that the higher hydroxylysine content of heart-valve collagen is responsible for the high degree of intermolecular cross-linking and may be the result of an adaptive mechanism for the specialized function of these tissues.

Amino Acids↗
PubMed2001

[Mechanical versus biological heart valves].

Since the first successful heart valve replacement procedures were performed in the 1950s, a multitude of different heart valves have been developed and implanted. This review offers a structured overview of the most important mechanical and biological heart valves with special regard to the individual indications of mechanical versus biological heart valve replacement and to possible postoperative complications.

Adult↗
PubMed1989

Heart valve replacement in septuagenarians.

Heart valve replacement was performed on 208 patients aged 70-80 years--aortic (AVR) in 172, mitral in 20 and both valves in 16 cases. All valves were of Björk-Shiley type, and all but six patients received maintenance oral anticoagulant therapy. The 100% follow-up comprised 744 patient-years (mean 4.0 years). The early mortality was 9.6% and was related to the complexity and urgency of surgery: After elective AVR for pure aortic stenosis the rate was 3.9%. Actuarial survival (early mortality excluded) was 79% at 5 years and 73% at 8 years overall, and 87% and 80% after AVR for stenosis. In the AVR group the relative (age- and -sex-adjusted) survival rate indicated a normalized survival pattern after the first year, with 87%, 'cure' rate (early mortality included), and the incidence of thromboembolism and of fatal bleeding complications equalled figures for younger patients. Mechanical heart valve implantation and maintenance anticoagulation thus seems to be safe treatment even in elderly patients, and eliminates need for valve re-replacement due to bioprosthetic degeneration.

Actuarial Analysis↗
PubMed1996

Mitral heart valve cavitation in an artificial heart environment.

BACKGROUND AND AIMS OF THE STUDY: The formation and subsequent collapse of vaporous cavities in the fluid around mechanical heart valves at valve closure can create stresses large enough to damage both the valve itself and blood cells. Improved understanding of cavitation mechanisms should lead to a reduction in the cavitation potential of future valve designs. MATERIALS AND METHODS: This study compares eight mechanical mitral valves of two different geometries (Monostrut and Medtronic Hall), occluder housing gaps (tight, medium, and leaky), and occluder materials (Delrin and pyrolytic carbon). The valves were evaluated in a model ventricle of the Penn State Electric Ventricular Assist Device (EVAD) operating within a mock circulatory loop. The EVAD represents one half of a total artificial heart. The mock loop consisted of silicone tubing connected to elements designed to mimic the compliant and resistant properties of the natural circulation. Cavitation was controlled by varying the degree of filling of the ventricle: low filling caused higher valve closing velocities resulting in greater cavitation intensities than complete filling of the ventricle. The intensity of cavitation was quantified using a parameter derived from the high frequency fluctuations in the mitral pressure that occur around the valve during cavitation events. The shape of the cavitation pressure signature and that of the power spectrum of the cavitation pressure signature were used in addition to the cavitation intensity parameter to make comparisons between valves. RESULTS: Of the three valve characteristics studied, occluder material showed the most significant influence on cavitation intensity: valves with pyrolytic carbon occluders demonstrated greater cavitation than did those with Delrin discs. CONCLUSION: It is hypothesized that the dominant form of cavitation on the valves studied is related to vortex formation and that occluder material influences the intensity of cavitation through the strength of the tension wave generated at valve closure, while geometry and gap have only secondary effects. Future studies are planned to incorporate this technique in an in vivo environment.

Biophysical Phenomena↗
PubMed1997

[Harvesting the heart for preparation of heart valve allografts].

Allograft heart valves (AHV) are believed to be optimal prosthetic material for surgical aortic valve and/or root replacement and an ideal valved conduit for repair of some complex congenital heart defects. At the University Hospital Motol AHV were clinically used since 1983 (annually no more than twenty were collected). 1991 the Paediatric Transplant Centre was established and was entrusted to organise cadaveric hearts harvesting and to introduce the standard technology of AHV processing and banking. The results of co-operation with other Transplants Centres, as well as with coroners and forensic medicine specialists in 1992-1995 are presented. For the AHV processing 274 cadaveric hearts were collected in the Czech and Slovak Republics, 32 of them (11.7%) came from routine post-mortem and 242 (88.3%) were retrieved from multiorgan harvesting, 14 hearts were excluded for technical reasons and another five for the seropositivity of the donor (three HBSAg, one HCV and one VDRL). Another 14 AHV were not suitable for clinical use because of a congenital lesion (bicuspid aortic valve) or acquired pathology found during the AHV processing (advanced atherosclerosis) or retrospectively diagnosed at donors post-mortem (in vivo undiagnosed malignancy). The technology of processing, cryopreservation and banking of AHV as well as the clinical use of the tissue will be discussed separately.

Cadaver↗
PubMed2003

Measurement of the closing behavior of the björk-shiley monoleaflet mechanical heart valve with an electrohydraulic total artificial heart.

When cavitation occurs near a material surface of a mechanical heart valve (MHV), pits on the surface of the MHV and hemolysis are caused. Therefore, it is very important to investigate the possibility of the occurrence of cavitation in an MHV. To study the possibility of cavitation occurrence in a 25 mm Björk-Shiley monoleaflet, we analyzed the closing behavior of these valves. The closing event of these valves in the mitral and aortic positions was simulated in an electrohydraulic total artificial heart with a stroke volume of 100 ml. Tests were conducted under physiologic pressures at heart rates of 50, 60, 70, and 80 beats/min with cardiac outputs of 4.8, 5.9, 7.0, and 8.1 l/min, respectively. The disk-closing behavior was measured by a laser displacement sensor. The closing behaviors were investigated with various cardiac outputs and gravity direction. The maximum velocities of the aortic valve ranged from 0.8 to 0.9 m/s, and for the mitral valve ranged from 1.48 to 1.6 m/s. In aortic position valves, the maximum closing velocities were less than the reported cavitation thresholds, but the maximum closing velocities of the mitral valve were similar to the cavitation threshold. Therefore, we suggest that there should be the possibility of cavitation occurrence in the mitral valve of an electrohydraulic total artificial heart.

Heart Valve Prosthesis↗