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At least 145 records · Page 8Linked to original sources
PubMed1999

The SynerGraft valve: a new acellular (nonglutaraldehyde-fixed) tissue heart valve for autologous recellularization first experimental studies before clinical implantation.

The durability of current bioprosthetic heart valves is diminished by glutaraldehyde-associated leaflet calcification or by the associated absence of a cellular component capable of repair of wear-related damage. As a novel tissue engineering approach to improving replacement heart valve durability, we have developed a decellularization process to replace the use of cross-linking to limit xenograft antigenicity. The effectiveness of this process was assessed in a weanling sheep right ventricular outflow tract reconstruction model where valve function, calcification, and recellularization were examined. Porcine aortic valves were decellularized by a process designed to remove all histologically demonstrable leaflet cells. Stentless, bioprosthetic valves were fabricated from acellular tissues, cryopreserved, sterilized, and then implanted as pulmonary valve replacements in 4- to 6-month old female Suffolk sheep. Sheep aortic valves were implanted as allograft control subjects. After 150 days, the grafts were explanted and assessed histologically and by atomic absorption spectrophotometry for calcium content. All valves were hemodynamically functional at explant. Histological examination showed intact leaflets with in-growth of host fibroblastoid cells in all explanted porcine valves and no evidence of calcification. Porcine leaflet calcium content was unchanged over the duration of the implant (1.0+/-1.2 vs 1.5+/-1.8 mg/g dry weight, P = ns). Decellularization can stabilize xenogenic heart valves. Lack of calcification of acellular aortic leaflets suggests that prolonged durability of such valves is attainable without the use of cross-linking agents. The repopulation of the leaflet matrix offers additional promise of durability based on revitalization of the graft in vivo.

Animals↗
PubMedDate not supplied

Support of cardiac performance following heart valve surgery by raising heart rate to the optimal pacing rate.

Effects of hemodynamic parameters of heart rate were studied in 19 patients with low cardiac output syndrome following open heart surgery for mitral and/or aortic valve replacement in the first five postoperative days. The central venous pressure (CVP), left atrial mean pressure (LAMP), and arterial blood pressures were determined at spontaneous heart rate (SHR), and during graded atrial (12 pts.) or ventricular (7 pts.) pacing each day. An "optimal pacing rate" (OPR), characterized by the most advantageous arterial pressures at the possible lowest levels of CVP and LAMP, and by the suppression of preexisting arrhythmias, if any, was established daily for maintaining each patient on that rate. The SHR was 69 +/- 9 and the OPR was 102 +/- 9 on the first postoperative day. For the fifth postoperative day the SHR was 68 +/- 10 and the OPR decreased to 90 +/- 9. Pacing with the OPR significantly increased cardiac performance. E.g. the hemodynamic improvement on the first postoperative day induced by pacing was comparable to the spontaneous improvement seen during the first five postoperative days. The hemodynamic effect of atrial pacing on circulation was more definitive than that of ventricular pacing. Since OPR may be significantly higher than SHR and varies from day to day, we suggest that, in cases where pacing is applied to improve cardiac performance, it be determined for each patient individually each postoperative day.

Adolescent↗
PubMedDate not supplied

Infective endocarditis in a hancock bioprosthetic heart valve.

Contemporary prosthetic heart valves (PHV) are a good mode of treatment of valvular heart disease. They last for an average of 5 to 10 years and bioprostheses fail due to the tissue degeneration. Infective endocarditis of the prosthetic valve is a relatively rare complication occurring in 0.5% to 1% of cases per year, and its late occurrence is even less common. Patients with PHV who undergo interventional or surgical procedures under adequate antibiotic coverage, infective endocarditis should not occur. We present a case of a 54-year-old woman who developed infective endocarditis on a porcine bioprosthesis, implanted 15 years earlier. The microorganism was Streptococcus viridans and the vegetations were surprisingly large and led to prosthesis obstruction.

Animals↗
PubMed1990

[Glutaraldehyde residues in heart valve prostheses].

Bioprosthetic heart valves prepared from glutaraldehyde-pretreated bovine pericardium are used to replace diseased human cardiac valves. Mineralisation in the course of time and toxic effects are possibly caused by glutaraldehyde residues. Different washing methods carried out before transplantation are compared with regard to the different ability of glutaraldehyde extraction.

Animals↗
PubMed2004

Innovative technologies for the assessment of cardiovascular medical devices: state-of-the-art techniques for artificial heart valve testing.

Prosthetic heart valves (PHVs) are engineered devices used for replacing diseased natural cardiac valves. This article presents several investigational techniques for the evaluation of the performance of these clinical devices, whose implantation is not completely free of drawbacks. The state-of-the-art in the technological approach for PHV testing is addressed. As the fluid dynamics of PHVs are particularly complex, the main focus will be on experimental velocimetric techniques and computational analysis. A methodology for the analysis of the valve's signature, in terms of its characteristic sound in the opening and closing phases, is also presented. The aforementioned techniques are necessary to guarantee an operational life of the implanted device as free as possible from clinical complications. It can be realistically expected that this characterization will help designers in improving PHV performance.

Biotechnology↗
PubMed1980

Long-term clinical and hemodynamic evaluation of the Ionescu-Shiley pericardial xenograft heart valve.

Pericardial xenograft heart valves have been used in 469 patients for single or multiple valve replacement. Early in the series, valves were made in-house, but since May 1976, valves have been made by Shiley Laboratories, Inc. During the eight-year observation period, there were 7% early and 7.9% late deaths. Although no anti-coagulants were used on a long-term basis, there were only eight mild embolic episodes. Preoperatively, 56--98% of all patients were in class III or IV of the NYHA classification; postoperatively, all surviving patients have been found to have improved by at least one classification.

Adolescent↗
PubMedDate not supplied

Mean velocity and Reynolds stress measurements in the regurgitant jets of tilting disk heart valves in an artificial heart environment.

Laser Doppler velocimetry, with a high temporal resolution (1 ms time windows), was used to measure the flow field in two regions (major and minor orifices) near the aortic and mitral valves (Bjork Shiley monostrut Nos. 25 and 27, respectively) of the Penn State artificial heart. The motion of each valve was also investigated using a 1000 frame/s video camera in order to estimate the valve's closing velocity. Fluid velocities in excess of and opposite to valve closing velocity were detected near the valve, providing evidence of "squeeze flow." Maximum Reynolds shear stresses of approximately 20,000 dyn/cm2 and time-averaged Reynolds shear stresses of approximately 2000 dyn/cm2 were observed during the regurgitant flow phase. These elevated Reynolds shear stresses suggest that regurgitant jets play a role in the hemolysis and thrombosis associated with tilting disk heart valves in an artificial heart environment.

Aortic Valve↗
PubMed2001

[Prevention of bacterial endocarditis in patients with prosthetic heart valves].

American Heart Association published in 1997 new version of recommendations for prevention of bacterial endocarditis in risk patients. Postoperative stadium in patients with prosthetic valve belongs to the highest risk. Infection can develop during bacteremia, which occurs most frequently at stomatologic and urologic interventions. The whole scale of medical interventions can be covered by two universal antibiotical regimes--one for the mouth, respiratory and upper GI tract, second for urogenital and lower GI tract. In the first case 2 g of Amoxicillin are administered p.o. 2 hours before the intervention. Interventions are individually listed, and cases where antibiotical prophylaxis is not recommended are separately given. Special situations are discussed.

Antibiotic Prophylaxis↗
PubMed2006

[Aortic valve stenosis: from valvuloplasty to percutaneous heart valve].

Calcified aortic stenosis is the predominant valve disease. Patients affected are most commonly elderly people, who often show associated comorbidities like reduced left ventricular function, impaired renal function, and pulmonary hypertension. The risk of open-heart surgery is elevated. Balloon aortic valvuloplasty enables a reduction of symptoms, an increase in physical performance, and, therefore, an improved quality of life. However, a reduction in mortality cannot be reached with this method. New techniques and improved equipment induced a "revival" of balloon aortic valvuloplasty, which has been introduced almost 20 years ago. In addition, brachytherapy after balloon valvuloplasty has recently been investigated and represents an interesting approach to reduce early restenosis. The technical improvement of balloon valvuloplasty is the percutaneous heart valve, which is under present clinical investigation. The antegrade/transseptal and retrograde approaches are used, as is the transapical access to the left ventricle. Even if long-term results are not yet available and the procedures still require technical improvement, especially minimization of catheter size, percutaneous valve replacement is a new chapter in the treatment of the calcified aortic stenosis.

Age Factors↗
PubMed2002

Tissue engineering of heart valves -- current aspects.

Tissue engineering of heart valves is an evolving research field. Driven by the shortcomings of the heart valve substitutes currently available, such as need for anticoagulation, susceptibility to infections, inability to grow and autorepair, the multidisciplinary approach for designing and growing viable heart valves identical to the native heart valves has begun. The following will give an update of the recent developments, current limitations and potential future applications of tissue-engineered heart valves.

Animals↗
PubMed2001

Microembolic signal counts increase during hyperbaric exposure in patients with prosthetic heart valves.

BACKGROUND: Patients with prosthetic heart valves have an increased risk of thromboembolic events, and transcranial Doppler sonography reveals microembolic signals. Whereas microembolic signals were initially assumed to be of particulate matter, recent studies suggest that they are partially gaseous in origin. If this is true, alteration of environmental pressure should change microembolic signal counts. We undertook this study to evaluate the influence of hyperbaric exposure on microembolic signal counts in persons with prosthetic heart valves. METHODS AND RESULTS: Microembolic signal counts were monitored by transcranial Doppler sonography of both middle cerebral arteries under normobaria (normobaria 1), 2 subsequent periods of hyperbaria (2.5 and 1.75 bar), and a second period of normobaria (normobaria 2) in 15 patients with prosthetic heart valves. Each monitoring period lasted 30 minutes. Compression and decompression rates were 0.1 bar/min. Microembolic signal counts increased from 20 (12-78) at normobaria 1 to 79 (30-165) at 2.5 bar (P <.01 vs normobaria 1 and 2), decreased to 44 (18-128) at 1.75 bar (P <.01 vs normobaria 1 and 2.5 bar; P <.001 vs normobaria 2), and returned to 20 (8-96) at normobaria 2 (values are medians and 95% confidence intervals). CONCLUSIONS: Our results strongly suggest that gaseous bubbles are underlying material for part of the microembolic signals detected in patients with prosthetic heart valves.

Aortic Valve↗
PubMed2003

Cavitation caused by mechanical heart valve prostheses--a review.

Heart valve dysfunction often necessitates surgical implantation of a mechanical heart valve (MHV). Although implantation of a MHV is a life-saving procedure, the patient still faces potentially complications such as thromboembolic events and material failure. These complications may be caused by cavitation, which can occur during valve closure. Cavitation is an erosive phenomenon that can be generated in fluids when the pressure locally drops below the vapor pressure. This paper reviews the literature on cavitation and MHVs and particular features of the valve and closing conditions that potentially increase the intensity of cavitation. Techniques for detecting cavitation will be discussed. Of these, an acoustic approach will be emphasized, since it is currently the only technique able to detect and quantify cavitation in vivo.

Heart Injuries↗
PubMed1996

Effect of valve holder flexibility on cavitation initiation with mechanical heart valve prostheses: an in vitro study.

BACKGROUND AND AIM OF THE STUDY: Several in vitro studies have reported on cavitation bubble visualization with mechanical heart valves and the cavitation intensity has been correlated with the design of the valve, the load on the valve occluder, the velocity of the occluder tip, and the negative pressure transients in the vicinity of the occluder. These studies demonstrated the presence of cavitation for certain types of valves under simulated normal physiological loading conditions. However, extrapolation of these results to cavitation initiation in vivo has been questioned due to limitations of the in vitro studies in simulating the in vivo tissue compliance. The present study was intended to analyze the effect of valve holder flexibility (simulating compliance of the suture ring and the surrounding tissue in vivo) on cavitation dynamics. METHODS: Cavitation bubbles were visualized on three types of mechanical heart valves (Medtronic Hall, Edwards-Duromedics, and CarboMedics) in our in vitro set up, and pressure transients were measured close to the occluder at valve closure. Two different flexible valve holders made of Teflon (elastic modulus, E = 400 MPa) and low density polyethylene (E = 180 MPa) were employed and the results were compared with those with a rigid Plexiglas holder (E = 2930 MPa) of the same geometry (3'' by 3'' wide and 1/8'' thick). RESULTS: Significant reductions were noted in the intensity of cavitation bubbles appearing along the clearance region of the Medtronic Hall and CarboMedics valves, with increasing valve holder flexibility. However, no attenuation was observed for the bubbles appearing around the seating lip or stop of the Edwards-Duromedics and Medtronic Hall valves that are believed to be caused by the fluid squeezing effect. CONCLUSIONS: The results of the study suggest that timing of the mechanism to initiate cavitation is a critical factor in cavitation attenuation with flexible valve holders. If cavitation is initiated before the flexible valve holder responds to the impact at valve closure (such as due to squeeze film effect), cavitation intensity remains unchanged. Based on the results of the study, we propose that tissue compliance in vivo may not attenuate cavitation initiation for certain types of mechanical heart valves depending on the cavitation initiation mechanism.

Biomechanical Phenomena↗
PubMed2000

Evolution of mechanical heart valves.

The need for prosthetic heart valves was long recognized but seemed an impossible dream before 1952 when Dr Charles Hufnagel clinically introduced a ball valve that he placed into the descending thoracic aorta for treatment of aortic valvular insufficiency. Fulfillment of that dream became a reality with the advent of extracorporeal circulation in the early 1950s. Development of prosthetic heart valves involved the search for biologically compatible materials and hemologically tolerant designs. Success could not be achieved without the union of these two factors. As there was no satisfactory mechanism to scientifically achieve this goal, trial and error was the method of choice. The development of prosthetic heart valves became the purview of the cardiovascular surgeon who often collaborated with engineers. To distinguish one valve from another each prosthesis often became identified with the surgeon developer. The development of bioprostheses occurred later in the development of artificial heart valves and constitutes a separate subject not covered in this presentation.

Heart Valve Prosthesis↗
PubMed1999

CarboMedics Prosthetic Heart Valve.

INTRODUCTION: The CarboMedics Prosthetic Heart Valve has been in use since 1986, with more than 220,000 valves implanted through August of 1997 in more than 1550 centers in more than 100 countries. This paper presents the results of a multicenter, international clinical trial that has spanned 10 years. METHODS: There were 1128 valves implanted in patients at 10 sites. The mean follow-up for patients was 4.5 years, with a total of 5110.1 patient-years. Approximately one-third of the patients came from the United States, one-third from Canada, and one-third from Scandinavia. The mean age was 57.2 years; 54.8% were men and 45.2% were women. The primary disease was calcification/atherosclerosis in 37% of the patients and rheumatic disease in 32.7%, and reoperation accounted for 17.5%. There were 556 aortic valve replacements, 428 mitral valve replacements, 139 double valve replacements, and five tricuspid replacements. RESULTS: The survival rate of all implanted patients was 79% at 5 years postoperatively. The survival rate in redo valve patients was as good as the primary survival rate; the survival rate in double valve patients was not as good as the survival rate in single valve patients. There was no structural failure of the valve. Patient outcome as described by New York Heart Association class was significantly improved throughout the postoperative period. Rates of freedom from thrombosis, thromboembolism, and hemorrhage at 5 years were 98.9%, 90%, and 91%, respectively. SUMMARY: Clinical results of the CarboMedics Prosthetic Heart Valve in a midterm, multicenter study were excellent, with low rates of morbidity and mortality and no structural failure.

Biocompatible Materials↗
PubMed2003

Antiplatelet and anticoagulation for patients with prosthetic heart valves.

BACKGROUND: Patients with prosthetic heart valves are at increased risk for valve thrombosis and arterial thromboembolism. Oral anticoagulation alone, or the addition of antiplatelet drugs, has been used to minimize this risk. An important issue is the effectiveness and safety of the latter strategy. OBJECTIVES: To compare the effectiveness and safety of adding antiplatelet therapy to standard oral anticoagulation among patients with prosthetic heart valves. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (Cochrane Library Issue 2, 2003), MEDLINE (January 1966 to August 2002), EMBASE (January 1988 to July 2001) and reference lists of individual reports, review articles, meta-analyses, and consensus statements. SELECTION CRITERIA: All reports of randomised controlled trials comparing standard dose oral anticoagulation to standard dose oral anticoagulation and antiplatelet therapy in patients with one or more prosthetic heart valves. We included reports published in any language or in abstract form. DATA COLLECTION AND ANALYSIS: Two reviewers independently performed the search strategy, assessed trials for inclusion criteria, study quality, and extracted data. Adverse effects information was collected from the trials. MAIN RESULTS: Eleven studies involving 2,428 subjects met the inclusion criteria. Year of publication ranged from 1971 to 2000. Compared with anticoagulation alone, the addition of an antiplatelet agent reduced the risk of thromboembolic events (odds ratio 0.39 (95% confidence interval 0.28 to 0.56; p<0.00001)) and total mortality (odds ratio 0.55 (95% confidence interval 0.40 to 0.77; p=0.0003)). Aspirin and dipyridamole reduced these events similarly. The risk of major bleeding was increased when antiplatelet agents were added to oral anticoagulants (odds ratio 1.66 (95% confidence interval 1.18 to 2.34; p=0.003)). For major bleeding, there was no evidence of heterogeneity between aspirin and dipyridamole and in the comparison of trials performed before and after 1990, around the time when anticoagulation standardization with the international normalized ratio was being implemented. REVIEWER'S CONCLUSIONS: Adding antiplatelet therapy, either dipyridamole or low-dose aspirin, to oral anticoagulation decreases the risk of systemic embolism or death among patients with prosthetic heart valves. The risk of major bleeding is increased with antiplatelet therapy. These results apply to patients with mechanical prosthetic valves or those with biological valves and indicators of high risk such as atrial fibrillation or prior thromboembolic events. The effectiveness and safety of low dose aspirin (100 mg daily) appears to be similar to higher dose aspirin and dipyridamole.

Anticoagulants↗