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PubMed2003

Tissue-engineered heart valve on acellular aortic valve scaffold: in-vivo study.

The feasibility of constructing a tissue-engineered heart valve on an acellular porcine aortic valve leaflet was evaluated. A detergent and enzymatic extraction process was developed to remove the cellular components from porcine aortic valves. The acellular valve leaflets were seeded for 7 days in vitro with cells from canine arterial wall and endothelial cells. The constructs were implanted into the lumens of 6 canine abdominal aortas to assess the reconstruction of the valve leaflets. It was found that all cellular components had been removed from the porcine aortic valves. The valve leaflets were completely reconstructed at the end of the 10th week in vivo. Scanning electron microscopy showed that the valve leaflets were partially covered with endothelial cells. It was concluded that porcine aortic valves can be decellularized by the detergent and enzymatic extraction process and it is feasible to construct a tissue-engineered heart valve in vivo on an acellular valve scaffold.

Animals↗

PubMed1995

Optimal oral anticoagulant therapy in patients with mechanical heart valves.

BACKGROUND: The optimal intensity of oral anticoagulant therapy for patients with mechanical heart valves (i.e., the level at which thromboembolic complications are effectively prevented without excessive bleeding) is not known. We attempted to determine the optimal intensity by calculating the incidence of both complications at different levels of anticoagulation. METHODS: Data were collected on all patients with mechanical heart valves who have been seen at four regional Dutch anticoagulation clinics since 1985. The primary outcome events were episodes of thromboembolism or major bleeding. The intensity-specific incidence of each type of event was calculated as the number of events that occurred at a certain intensity of anticoagulation (expressed in terms of the international normalized ratio [INR]) divided by the number of patient-years during which the INR was at this level in the total patient population. RESULTS: A total of 1608 patients were followed during 6475 patient-years. Cerebral embolism occurred in 43 patients (0.68 per 100 patient-years) and peripheral embolism in 2 (0.03 per 100 patient-years). Intracranial and spinal bleeding occurred in 36 patients (0.57 per 100 patient-years) and major extracranial bleeding in 128 (2.1 per 100 patient-years). The optimal intensity of anticoagulation, at which the incidence of both complications was lowest, was achieved when the INR was between 2.5 and 4.9. CONCLUSIONS: The intensity of anticoagulant therapy for patients with prosthetic heart valves is optimal when the INR is between 2.5 and 4.9. To achieve this level of anticoagulation, a target INR of 3.0 to 4.0 is recommended.

Acenocoumarol↗

PubMed2003

Fondaparinux and enoxaparin in comparison to unfractionated heparin in preventing thrombus formation on mechanical heart valves in an ex vivo rabbit model.

The aim of the present study was to investigate the efficacy of three different parenterally administered anticoagulants for the prevention of thrombus formation on artificial heart valves in an experimental rabbit model. Unfractionated heparin was administered intravenously in group I (n = 10), Enoxaparin subcutaneously in group II (n = 10), fondaparinux intravenously in group III (n = 10), and no medication was administered to group IV (n = 9). Leaflets from Sulzer Carbomedics bileaflet mechanical heart valves were placed in a flow chamber. The flow chamber was filled with blood in a continuous circulation between the carotid artery and the jugular vein. In group IV the flow chamber was clotted after a median of 15 minutes of circulation. Weight analysis before and after 1 h of perfusion showed that the median thrombus weight was 18.0 mg in group I, 17.7 mg in group II, 20.3 mg in group III, and 30.8 mg in group IV. Further analysis by electron microscopy showed similar results regarding deposition of fibrin, platelets, and erythrocytes on leaflet surfaces. Fondaparinux and subcutaneously administered enoxaparin were as effective as intravenously administered unfractionated heparin in preventing thrombus formation on artificial heart valve leaflets in our investigation. This rabbit model, in which the heart valve leaflets were exposed to rabbit blood for a short time under laminar flow, should be further evaluated with respect to whether it can provide information about anti-thrombotic regimens in patients after mechanical heart valve replacement.

Animals↗

PubMed1989

[Subjective noise perception and objective measurement of loudness following heart valve replacement with the St. Jude Medical and Duromedics Edwards bileaflet prostheses].

The performance of heart valve prostheses is generally judged by the rate of valve-related complications and the hemodynamic performance. Patients may be severely bothered by the metallic click generated by the closure of the valve. In 74 patients after valve replacement with Duromedics Edwards (DE) (n = 38) and St. Jude Medical (SJM) (n = 36) prostheses the sound energy was recorded and correlated to the complaints of the patients. At a distance of 10 cm the DE valves produced a significantly higher sound pressure with 47 +/- 7 db(A) compared to the SJM valves with 39.8 +/- 5 db(A) (p = 0.001). The noise level was also different for the valves in aortic or mitral position. After splitting into frequency bands the highest sound pressure was observed in the high frequency ranges (8 to 16 kHz) which represents the metallic click. 65% of patients were aware of the noise generated by the valve, 16% had sleep disturbances and 22% would prefer a more silent valve type. 12 of 38 patients with DE valves and 4 of 36 patients with SJM valves wished to have a less noisy valve type (Chi square p = 0.003). In annoyed patients the valves produced a higher sound amplitude of 49 +/- 8 db(A) as compared to undisturbed patients with 42 +/- 6 db(A) (p = 0.002). The noise level of mechanical heart valves should be considered before selection of a prosthesis, because the metallic click bothers patients and the complaints correlate with measured sound energy.

Adult↗

PubMedDate not supplied

Dynamic characterization of a new accelerated heart valve tester.

This paper presents a new accelerated prosthetic heart valve tester prototype that incorporates a camshaft and poppet valves. A three element Windkessel system is used to mimic the afterload of the human systemic circulation. The device is capable of testing eight valves simultaneously at a rate up to 1,250 cycles/min, while the flow rate, the pressure, and the valve loading can be monitored and adjusted individually. The tester was characterized and calibrated using a set of eight Carpentier-Edwards bioprostheses at a flow rate varying between 3 and 5 L/min. The experiment was carried out with the pressure difference across the closed heart valve maintained between 140 and 190 mmHg. Smooth and complete opening and closing of the valve leaflets was achieved at all cycling rates. This confirms that the velocity profiles approaching the test valves were uniform, an important factor that allows the test valves to open and close synchronously each time.

Animals↗

PubMed2001

Prosthetic heart valves and annuloplasty rings: assessment of magnetic field interactions, heating, and artifacts at 1.5 Tesla.

The purpose of this study was to determine the magnetic resonance (MR) safety aspects and artifacts for three different heart valve prostheses and two different annuloplasty rings that have not been evaluated previously in association with the 1.5-T MR environment. Ex vivo testing was performed using previously described techniques for the evaluation of magnetic field interactions (deflection angle and torque), heating (gel-filled phantom and fluoroptic thermometry; 15 min of MR imaging at a whole body-averaged specific absorption rate of 1.2 W/kg), and artifacts (using T1-weighted, spin echo, and gradient echo pulse sequences). One heart valve prosthesis and one annuloplasty ring showed no magnetic field interactions. Two heart valve prostheses and one annuloplasty ring displayed relatively minor magnetic field interactions (i.e., deflection angle < or = 6 degrees, torque, +1). Heating was < or = 0.7 degrees C for the five different implants. Artifacts varied depending on the amount and type of metal used to make the implants. For the three heart valve prostheses and two annuloplasty rings, the lack of substantial magnetic field interactions and relatively minor hearing indicated that MR procedures may be conducted safetly in patients with these implants using MR systems operating with static magneticfields of 1.5 T or less. Notably, these findings essentially apply to 54 different heart valve prostheses and 37 different annuloplasty rings (i.e., based on the various models and sizes available for these implants).

Artifacts↗

PubMed2004

A new model to test the calcification characteristics of bioprosthetic heart valves.

BACKGROUND: Tissue degeneration and calcification are the two chief obstacles to the successful application of bioprosthetic heart valves. To enable the study of the durability of bioprosthetic heart valves and the efficacy of anti-calcification treatment, it has become necessary to develop animal models. The aim of this study is to validate a new model for implantation in the pulmonary position. METHODS: Three juvenile sheep underwent implantation of Carpentier-Edwards pericardial valves in the pulmonary position (experimental group). These three valves were compared with three Carpentier-Edwards pericardial valves in the aortic position in patients which had been explanted due to primary tissue failure (clinical group). The valves were analyzed. RESULTS: The findings of macroscopic, X-ray and light microscopic examination were very similar between the two groups. Scattered irregular calcification was seen near the commissures and at the base of the cusps in both groups. Quantitative calcium content analysis showed that calcification of the cusps had progressed to almost the same degree in both groups (experimental group, 3.7+/-0.2 micro g/mg dry tissue; clinical group, 4.3+/-0.3; p>0.05). In the experimental group, calcification in the commissural area of the cusp was pronounced (6.5+/-1.0). In the clinical group, calcification had also progressed in the commissural area of the cusp (6.0+/-1.5), and extended to the base area of the cusp (6.6+/-1.2). CONCLUSIONS: This model is promising for preclinical evaluation of bioprosthetic heart valves. The degree of calcification is not significantly different between our experimental results after three months of implantation in sheep and clinical results after 10 years of implantation in elderly patients. However, the pattern of calcification is somewhat different between the two groups.

Aged↗

PubMed1996

The sheep as an animal model for heart valve research.

The first test used to assess new heart valve prostheses and devices is to implant them in a medium-sized animal. This is a costly piece of research and it is important to select the most appropriate animal. The authors feel that the sheep is an appropriate animal model for heart valve research and describe their experience in this area. It is hoped that the detailed description provided will be useful to any other group contemplating similar studies.

Animals↗

PubMed2000

Anticoagulation of pregnant women with mechanical heart valves: a systematic review of the literature.

BACKGROUND: The management of women with prosthetic heart valves during pregnancy poses a particular challenge as there are no available controlled clinical trials to provide guidelines for effective antithrombotic therapy. Oral anticoagulants such as warfarin sodium cause fetal embryopathy; subcutaneous administration of heparin sodium has been reported to be ineffective in preventing thromboembolic complications. OBJECTIVE: To identify the risks of maternal and fetal complications in women with mechanical heart valves treated with different anticoagulation regimens during pregnancy. METHODS: We performed a systematic review of the literature to determine pooled estimates of maternal and fetal risks associated with the 3 commonly used approaches: (1) oral anticoagulants (OA) throughout pregnancy, (2) replacing OA with heparin in the first trimester (from 6-12 weeks' gestation), and (3) heparin use throughout pregnancy. Fetal outcomes included spontaneous abortions and fetopathic effects, and maternal outcomes were major bleeding, thromboembolic complications, and death. RESULTS: The use of OA throughout pregnancy is associated with warfarin embryopathy in 6.4% (95% confidence interval [CI], 4.6%-8.9%) of livebirths. The substitution of heparin at or prior to 6 weeks, and continued until 12 weeks, eliminated this risk. Overall risks for fetal wastage (spontaneous abortion, stillbirths, and neonatal deaths) were similar in women treated with OA throughout, compared with women treated with heparin in the first trimester. Maternal mortality was 2.9% (95% CI, 1.9%-4.2%). Maj or bleeding events occurred in 2.5% (95% CI, 1.7%-3.5%) of all pregnancies, most at the time of delivery. The regimen associated with the lowest risk of valve thrombosis (3.9%; 95% CI, 2.9-5.9%) was the use of OA throughout; using heparin only between 6 and 12 weeks' gestation was associated with an increased risk of valve thrombosis (9.2%; 95% CI, 5.9%-13.9%). CONCLUSIONS: Thromboembolic prophylaxis of women with mechanical heart valves during pregnancy is best achieved with OA; however, this increases the risk of fetal embryopathy. Substituting OA with heparin between 6 and 12 weeks reduces the risk of fetopathic effects, but with an increased risk of thromboembolic complications. The use of low-dose heparin is definitely inadequate; the use of adjusted-dose heparin warrants aggressive monitoring and appropriate dose adjustment. Large prospective trials to determine the best regimen for these women are needed.

Administration, Oral↗

PubMed2004

Decision guidelines for prophylactic replacement of Björk-Shiley convexo-concave heart valves: impact on clinical practice.

BACKGROUND: Because of risk of outlet strut fracture, prophylactic replacement should be considered for Björk-Shiley convexo-concave (BScc) valve recipients. We assessed the effects of epidemiological and decision-analytic guidelines on actual BScc valve replacement. METHODS AND RESULTS: We performed a retrospective cohort study including all 2263 Dutch BScc patients with a mean follow-up of 11.3 years (range, 0 to 23 years). Outcomes were outlet strut fracture, mortality, and BScc valve replacement. For the surviving patients in 1992 (n=1330), we calculated the expected differences in life expectancy (LE) with and without BScc valve replacement according to decision guidelines developed in 1992. Differences in LE were compared with actual replacements. During 8 years of follow-up, there were 494 deaths (40%), and 11 patients had suffered outlet strut fracture. Of 1330 patients, 96 (10%) had undergone BScc valve replacement, particularly in years after introduction of initial and updated guidelines. One hundred seventeen patients (9%) had an estimated gain in LE after BScc valve replacement. These patients were more likely to undergo replacement than patients with an estimated loss of LE (hazard ratio, 6.6; 95% CI, 4.4 to 10; P<0.0001). A loss in LE after reoperation was predicted for 8 of 11 patients who experienced outlet strut fracture after guidelines were available. CONCLUSIONS: Valve replacement for BScc heart valve patients was largely in concordance with guidelines in the Netherlands. Individualized guidelines that are based on high-quality epidemiological data and are updated and implemented rigorously can influence clinical practice in complex decision problems.

Adult↗

PubMed2002

Prosthetic heart valves with silver-coated sewing cuff fabric: early morphological features in two patients.

BACKGROUND: The current generation of prosthetic heart valves are excellent examples of engineering that work well, for long periods of time. Unfortunately, host-related problems and consequent valve failure continue to occur, including infective endocarditis. St Jude Medical Inc introduced a new model of mechanical heart valve prosthesis with silver-treated fabric to try to reduce the incidence of infective endocarditis. Two cases of failure of this prosthesis, with a clinical diagnosis of infective endocarditis, are presented. MATERIALS AND METHODS: Of the 176 St Jude Medical Silzone-coated prostheses implanted, two were explanted in the first half of 1998. The clinical status of the patients was reviewed, and a detailed gross, histological and stereomicroscopic examination of the prosthetic valves was undertaken. RESULTS: Clinically, both patients developed symptoms of infective endocarditis. The first patient developed features of a stroke and two months later underwent a second valve replacement. The prosthesis showed pannus and thrombus. A paravalvular leak was revealed in the second patient, who underwent a second valve replacement six months after the initial surgery. Blood and tissue cultures were negative in both cases. CONCLUSIONS: The new model St Jude Medical Silzone mechanical heart valve prosthesis, designed to prevent infective endocarditis, was associated with clinical features of endocarditis in these two cases. Significant pannus and thrombus were seen on both prostheses, which likely led to emboli and stroke in the first case. The cause of the paravalvular abscess in the second case has not yet been established. The early failure of these prostheses suggests that patients with this prosthesis be followed up carefully.

Endocarditis, Bacterial↗

PubMed2001

[Multiple heart valve diseases: differential therapeutic considerations].

After more than 40 years of heart valve surgery, the indication for double valve procedures still represents a problem in the presence of an obviously leading single valve disease. If the isolated valves do not already represent a clear indication for surgery then this situation is the best example for a good deal of thought in cardiac surgery and discussion with competent cardiologists.

Adult↗

PubMed2003

The optimal intensity of vitamin K antagonists in patients with mechanical heart valves: a meta-analysis.

OBJECTIVES: The purpose of this study was to compare two different intensities of vitamin K antagonists (VKA) among patients with mechanical heart valves using meta-analytic techniques. BACKGROUND: Patients with mechanical heart valves are at increased risk for valve thrombosis and systemic embolism, which can be reduced by VKA. The range of optimal intensity of VKA is still a matter of debate. METHODS: A computerized search in the PubMed database was made for relevant articles. A meta-analysis was performed of all eligible studies with data on the incidences of thromboembolic and bleeding complications in patients with mechanical heart valve prostheses during different intensities of VKA therapy. The studies were classified into low-intensity VKA therapy (mean target international normalized ratio [INR] of 3.0 or lower) or high-intensity VKA therapy (mean target INR above 3.0). RESULTS: Thirty-five eligible studies were identified, including in total 23,145 patients, who were studied for 108,792 patient-years. For patients with an aortic valve, high intensity resulted in a lower incidence of thromboembolic events (risk ratio [RR] = 0.73, p < 0.0001); however, the incidence of bleeding was increased (RR = 1.23, p < 0.0001). In the mitral valve group, the incidence rate for thromboembolism was lower in the high-intensity group (RR = 0.74, p < 0.0001), without a significantly increased bleeding incidence (RR = 1.08, p = 0.0524). The total number of thromboembolic and bleeding events was decreased in the high-intensity group compared with low-intensity VKA therapy for both aortic and mitral valve prostheses (RR = 0.94 [p = 0.0067] and 0.84 [p < 0.0001]), respectively. CONCLUSIONS: This meta-analysis shows that both aortic and mitral valves will benefit from a treatment strategy with a target INR higher than 3.0.

Aortic Valve↗

PubMed2004

Blood serum apolipoproteins B and A-I in females suffering from rheumatic heart valve disease.

OBJECTIVE: With the aim to check whether the atherogenic factors are involved in the mechanisms of valve fibrosis, we have studied the blood serum concentrations of apolipoproteins (apo) A-I and B concentration in patients suffering from rheumatic heart valve fibrosis. METHOD: The quantities of apoA-I and apoB in the blood serum were tested by the ELISA method. Concentration of apoA-I and B in the blood serum was determined in rheumatic females with replacement of the damaged valves: after aortic valve operation (n=11; mean age 43.3+/-3.6 years) and after mitral valve operation (n=29; 41.3+/-4.1). The results obtained for rheumatic patients were compared with the data on age-matched healthy females (n=43; 39.5+/-5.2 years). RESULTS: Significantly lower apoA-I level in the blood serum of all patients suffering from rheumatic heart valve disease was determined as compared with controls: in the pooled group of patients (1.02+/-0.22 vs 1.23+/-0.23 g/l, P<0.001), in women after aortic valve replacement (0.98+/-0.21 vs. 1.23+/-0.23 g/l, P<0.005), and in women after mitral valve surgery (1.03+/-0.23 g/l vs 1.23+/-0.23 g/l, P<0.005). The apoB level in patients suffering from rheumatic heart valve disease did not differ from that of controls. The apoB/apoA-I ratio for patients with valve fibrotic damage was significantly higher as compared to controls in all groups (P<0.02). The increase of apoB/apoA-I ratio in patients with rheumatic valve fibrosis was caused by lower apoA-I levels in blood serum. CONCLUSION: The obtained results indicate that decreased apoA-I levels in blood serum can be indicative of valve fibrosis in rheumatic heart valve disease patients.

Adult↗

PubMed1996

The cost of treating heart valve related complications.

BACKGROUND AND AIM OF THE STUDY: Heart valve replacement can result in serious complications. Therefore, it is important in decision making regarding the choice of valves to know the cost of such complications. METHODS: Complications were defined according to guidelines proposed by the Society of Thoracic Surgeons. They included valve thrombosis, embolism, hemorrhage due to anticoagulation, non-structural dysfunction, structural deterioration and endocarditis. The costs of the pre-admission assessment, acute inpatient stay, inpatient physician fees, post-discharge and out-patient physician fees were estimated for each complication to determine the average total cost in 1995 US dollars. Cost inputs were obtained from existing Massachusetts databases and Medicare fee schedules. RESULTS: The costs of managing valve thrombosis, endocarditis and non-structural dysfunction were all estimated to exceed $30,000 for a single event. The costs of acute management of embolism and anticoagulant-related hemorrhage were between $8,000 and $11,500. However, it is of note that managing the sequelae of an embolism was calculated to be greater than $70,000 over 15 years. The greatest contributor to the average cost of treating a complication was determined to be the in-patient facility cost. CONCLUSIONS: Complications related to heart valve replacement can be very costly to manage in both the short term and the long term.

Costs and Cost Analysis↗

PubMed1994

In vitro observations of mechanical heart valve cavitation.

The in vitro cavitation thresholds and locations were studied on ten different heart valve designs. The valves were mounted in a mock circulation flow loop which simulated a cardiovascular system. All the tests were run at 70 beats per minute with a cardiac output varying between 2 l/min and 6 l/min in increments of 1 l/min. In vitro cavitation phenomena generated at the closing instant of mechanical heart valves were captured using a video photographic technique. Cavitation locations and intensity on different valve designs were analyzed from the cavitation images recorded on a video tape. When cavitation occurs on a bileaflet valve, it can occur in the same localized area of the leaflet from cycle to cycle thus producing a cumulative effect. In a single disc valve, the free rotation of the valve disc during operation provides a means of distributing a localized cavitation activity over an ever changing disc surface. Thus any cavitation-induced damage on the disc surface can be reduced or eliminated even though a single disc valve may have a lower cavitation threshold. Cavitation locations and thresholds are primarily a function of valve design. Smaller size valves have higher cavitation thresholds than larger ones. The cavitation thresholds of all the valves tested were above the physiological left ventricular maximum dp/dt at rest. If in vivo cavitation occurs under some extreme conditions, this study suggests possible locations on mechanical heart valves which could be examined for traces of cavitation activity.

Cardiac Output↗

PubMed2001

Enoxaparin treatment in women with mechanical heart valves during pregnancy.

OBJECTIVE: This prospective audit reports pregnancy outcomes, anticoagulation complications, and anti-Xa levels in women with mechanical heart valves who were treated with therapeutic enoxaparin plus aspirin during pregnancy. STUDY DESIGN: Between 1997 and 1999, 11 women with mechanical heart valves were treated with enoxaparin, 1 mg/kg twice daily, and aspirin, 100 to 150 mg daily during 14 pregnancies. Predose and 4-hour postdose anti-Xa levels were monitored monthly. RESULTS: There were 9 live births, 3 miscarriages, and 2 terminations. In 48 months of enoxaparin treatment, one woman who had a documented valve thrombosis when she presented at 8 weeks' gestation also had a valve thrombosis at 20 weeks' gestation. There were no enoxaparin-related hemorrhagic complications. Mean (SD) anti-Xa levels were 0.46 (0.12) U/mL predose and 0.89 (0.22) U/mL 4 hours postdose. CONCLUSION: Successful pregnancy outcome may be achieved with therapeutic subcutaneous enoxaparin, but its efficacy at preventing valve thrombosis remains uncertain. Further data are required before use of enoxaparin during pregnancy in women with mechanical heart valves can be recommended.

Adult↗

PubMed2006

Tissue engineering of heart valves by recellularization of glutaraldehyde-fixed porcine valves using bone marrow-derived cells.

To increase the biocompatibility and durability of glutaraldehyde (GA)-fixed valves, a biological coating with viable endothelial cells (ECs) has been proposed. However, stable EC layers have not been formed successfully on GA-fixed valves due to their inability to repopulate. In this study, to improve cellular adhesion and proliferation, the GA-fixed prostheses were detoxified by treatment with citric acid to remove free aldehyde groups. Canine bone marrow mononuclear cells (MNCs) were differentiated into EC-like cells and myofibroblast-like cells in vitro. Detoxified prostheses were seeded and recellularized with differentiated bone marrow- derived cells (BMCs) for seven days. Untreated GA-fixed prostheses were used as controls. Cell attachment, proliferation, metabolic activity, and viability were investigated and cell-seeded leaflets were histologically analyzed. On detoxified GA-fixed prostheses, BMC seeding resulted in uninhibited cell proliferation after seven days. In contrast, on untreated GA-fixed prostheses, cell attachment was poor and no viable cells were observed. Positive staining for smooth muscle a-actin, CD31, and proliferating cell nuclear antigen was observed on the luminal side of the detoxified valve leaflets, indicating differentiation and proliferation of the seeded BMCs. These results demonstrate that the treatment of GA-fixed valves with citric acid established a surface more suitable for cellular attachment and proliferation. Engineering heart valves by seeding detoxified GA-fixed biological valve prostheses with BMCs may increase biocompatibility and durability of the prostheses. This method could be utilized as a new approach for the restoration of heart valve structure and function in the treatment of end-stage heart valve disease.

Actins↗