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At least 613 records · Page 34Linked to original sources

PubMedDate not supplied

A comparative study in patients with Omnicarbon and Björk-Shiley heart valve replacement.

To compare the Omnicarbon heart valve and the Björk-Shiley spherical valve, operative results, hemodynamic parameters and late results were examined after mitral valve replacement. There were no early deaths, and 6 late deaths in the Omnicarbon valve (2.9% per patient-year). The actuarial survival rate at 6 years was 82.1 +/- 4.8% and freedom from valve-related complications was 86.4 +/- 2.2%. Pressure gradients and effective mitral valve areas at rest calculated by Gorlin's formula were satisfactory in both valve. Cardiac index (l/min/m2) was slightly changed according to the pacer-induced tachycardia, but there was a significant decrease in 160 bpm in the Omnicarbon valve (2.01 vs 2.39, p < 0.05). Peak pressure gradients and pressure half time by Doppler echocardiography, revealed the same trends as those of the Björk-Shiley valve during tachycardiac exercise, though regurgitant flow was detected in 7 patients in 160 bpm in the Omnicarbon valve, while in 2 in the Björk-Shiley valve (28% vs 10%, p = ns). Phonocardiographic study demonstrated that aortic closure to mitral opening click (AC-OpC) interval and Q wave of the electrocardiogram to mitral closing click (Q-CC) interval, which were related to the mitral valve gradients, fell within the normal range in both valves. However, the Björk-Shiley valve compared favorable to the Omnicarbon valve in the AC-OpC interval (70.9 msec vs 76.8 msec, p < 0.05). Hemolysis was of no clinical importance in the intact function of the Omnicarbon valve.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2003

Early results of a new mechanical tri-leaflet heart valve prosthesis--"Tricusp": an animal study.

OBJECTIVE: A new tri-leaflet mechanical heart valve made of titanium was inserted in the mitral position to evaluate early results. METHODS AND RESULTS: Five sheep were followed between 3 and 6 months (mean 4.7 months) and performed very well clinically during the follow-up period. In three of five animals a minor para-valvular leakage without hemodynamic importance was observed. The invasive pressure measurements at the end of follow-up revealed only minor transvalvular pressure differences between 1 and 4 mmHg (mean 2.4 mmHg). Similar results were obtained by echo-Doppler technique. Histological examination of the tissue around the valve showed no signs of foreign body reaction or chronic inflammatory reaction. CONCLUSION: This new tri-leaflet heart valve has shown an excellent hemodynamic performance and good tissue compatibility, and therefore may be an alternative to other currently used valve prostheses.

Animals↗

PubMed2006

An experimentally derived stress resultant shell model for heart valve dynamic simulations.

In order to achieve a more realistic and accurate computational simulation of native and bioprosthetic heart valve dynamics, a finite shell element model was developed. Experimentally derived and uncoupled in-plane and bending behaviors were implemented into a fully nonlinear stress resultant shell element. Validation studies compared the planar biaxial extension and three-point bending simulations to the experimental data and demonstrated excellent fidelity. Dynamic simulations of a pericardial bioprosthetic heart valve with the developed shell element model showed significant differences in the deformation characteristics compared to the simulation with an assumed isotropic bending model. The new finite shell element model developed in the present study can also incorporate various types of constitutive models and is expected to help us to understand the complex dynamics of native and bioprosthetic heart valve function in physiological and pathological conditions.

Animals↗

PubMed1980

Myxomatous degeneration of the heart valves in blacks.

Ten cases of myxomatous degeneration of the heart valves in Black subjects are described. The striking features, compared with other series, were the comparative youth of the patients and the predominance of aortic valve involvement. There was also a significant percentage of control subjects with excess mucopolysaccharides in the heart valves or aorta. These pathological findings confirm clinical observations previously made by other workers.

Adult↗

PubMed1995

Transcranial Doppler ultrasound signals associated with prosthetic heart valves: an in vitro study.

The application of transcranial Doppler (TCD) ultrasonography to asymptomatic prosthetic heart valve patients can result in detection of localized bursts of high intensity signals, similar to those caused by the passage of emboli. The origin of these signals is not known. In order to investigate this phenomenon in a simplified, more controllable environment, a TCD machine was used to record flow downstream from mechanical prosthetic heart valves in a mock circulatory loop. The model, which uses a saline solution seeded with silk particles (< 15 micrometers) as the circulatory fluid, recreates the principal hydrodynamic characteristics of the left heart and systemic circulation. Reproducibility of the system was established through repeated testing of a Monostrut valve. Three different mechanical valve types, (Monostrut, Medtronic Hall, St. Jude Medical) were tested over a range of simulated cardiac outputs, and the effect of valve size was investigated with four Omniscience tilting disc valves (21, 23, 25 and 29 mm). Average energy of the reflected Doppler signal was used to quantify the amount of high intensity Doppler signal, QTCD. TCD signals recorded in vitro were visually and aurally similar to those found in prosthetic heart valve patients. All valve types generated exponentially more QTCD with increasing simulated cardiac output. Differences amongst valve types were only significant at higher flow outputs, with the Monostrut valve producing the greatest QTCD. Larger valves consistently generated greater QTCD than smaller valves. In conclusion, TCD signals found in prosthetic heart valve patients can be reproduced, at least qualitatively, using a mock circulatory loop which does not incorporate the formed elements of blood.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Valve↗

PubMed1998

Comparative assessment of hepatic Glisson's capsule and bovine pericardium in heart valve bioprostheses.

BACKGROUND AND AIM OF THE STUDY: The optimal material for heart valve bioprostheses remains disputable. This investigation was initiated to compare the properties of hepatic Glisson's capsule, clinical experience of which in cardiovascular surgery is minimal, with those of bovine pericardium. METHODS: Hepatic Glisson's capsule was harvested from bull calves and used to create composite pulmonary arterial monocusp grafts and bioprostheses. Comparison of the strength and elastic properties of Glisson's capsule and bovine pericardium, as well as the hydrodynamic characteristics of valves made from these materials, was performed. Late results of operations using these materials were estimated echocardiographically. RESULTS: Although Glisson's capsule tissue is thinner than the bovine pericardium, its elasticity modulus is greater. However, the hydrodynamic characteristics of heart valves made from either tissue are similar. Moreover, valves made from Glisson's capsule have a lower systolic pressure gradient on the prosthesis and a higher effective orifice area. Composite pulmonary arterial xenopericardial grafts with a monocusp of Glisson's capsule were used in 30 patients during tetralogy of Fallot repair. Glisson's capsule was also used for tricuspid valve reconstruction and as a bioprosthesis in six patients with Ebstein's anomaly. At 1-2 years after surgery, the Glisson's capsule tissue remained thin and flexible, with no calcification. CONCLUSIONS: Although the hydrodynamic properties of hepatic Glisson's capsule and the bovine pericardium are similar, the capsule tissue is thinner and has a greater elasticity modulos. Thus, Glisson's capsule may be used for bioprosthesis construction both independently and in combination with bovine pericardium.

Animals↗

PubMedDate not supplied

Factors influencing patient knowledge of warfarin therapy after mechanical heart valve replacement.

BACKGROUND AND RESEARCH OBJECTIVE: Patients with mechanical heart valves must follow lifelong warfarin therapy. Warfarin, however, is a difficult drug to manage because it has a narrow therapeutic window and potentially serious side effects. Successful anticoagulation treatment is dependent upon the patient's knowledge of this drug; however, little is known regarding the determinants of such knowledge. Therefore, the purpose of this study was to determine the influence of both in-hospital teaching practices as well as socioeconomic status and demographic variables on patients' knowledge of warfarin therapy. SUBJECTS AND METHODS: A telephone survey was conducted among 100 patients 3 to 6 months after mechanical heart valve replacement. A previously validated 20-item questionnaire was used to measure the patient's knowledge of warfarin, its side effects, and vitamin K food sources. Demographic information, socioeconomic status data, and medical education information were also collected. Knowledge scores were compared using the Student t test or one-way analysis of variance. Variables with P < or = .2 on univariate analysis were entered in multiple stepwise regression analysis. RESULTS AND CONCLUSIONS: Sixty-one percent of participants had scores indicative of insufficient knowledge of warfarin therapy (score < or = 80%). Age was negatively related to warfarin knowledge scores (r = 0.27, P = .007). Patients with family incomes greater than $25,000, who had greater than a grade 8 education, and who were employed or self-employed had significantly higher warfarin knowledge scores (P = .007, P = .002, and P = .001, respectively). Gender, ethnicity, and warfarin therapy before surgery were not related to warfarin knowledge scores. Furthermore, none of the in-hospital teaching practices significantly influenced knowledge scores, whereas receiving postdischarge community counseling significantly improved knowledge scores (P = .001). Multivariate regression analysis revealed that understanding the concept of International Normalized Ratio, knowing the acronym, age, and receiving community counseling after discharge were the strongest predictors of warfarin knowledge. Accessing postdischarge counseling resulted in significantly improved warfarin knowledge scores. Because improved knowledge has been associated with improved compliance and control, our findings support the need to develop a comprehensive postdischarge education program or at least to ensure that patients have access to a community counselor to compliment the in-hospital education program.

Anticoagulants↗

PubMed1996

Valve design characteristics and cine-fluoroscopic appearance of five currently available bileaflet prosthetic heart valves.

Bileaflet prostheses are low profile, central flow orifice devices that show excellent hemodynamic performance and low thrombogenicity. Five models are currently used for heart valve replacement. Comprehensive and comparative studies regarding valve characteristics and functioning are lacking, making the updating and the familiarization by physicians and cardiologists with these prostheses difficult. We describe the valve design characteristics and evaluate the cine-fluoroscopic appearance and functioning of 387 bileaflet prostheses that have been implanted in 367 consecutive patients. The valve types are St Jude Medical (n = 69), Edwards-Duromedics (n = 74), Carbomedics (n = 1290) Sorin Bicarbon (n = 88) and Jyros (n = 27). The prostheses' fluoroscopic appearance was evaluated through multiple radiographic views (Siemens-Elema equipment with C-arm); the prostheses' functional evaluation was performed by obtaining the "tilting disk projection" (ie, with the radiographic beam parallel to both the valve ring plane and the tilting axis of disks) to calculate opening, closing, and travel angles of the disks. This study shows that each of the five bileaflet valves has distinctive design characteristics. Fluoroscopy is an easy, readily available, and useful technique that correctly identifies the prosthesis type and properly evaluates its functioning in the majority of cases.

Aortic Valve↗

PubMed1997

D-dimer and anticoagulation in patients with mechanical prosthetic heart valves. A 2-year follow-up.

The best anticoagulation level in patients with mechanical heart valve prostheses is still being debated. D-dimer, which detects the presence of cross-linked fibrin degradation products, has been demonstrated to be a useful marker of coagulation activation. This study was designed to verify whether heart valve prostheses in anticoagulated patients are associated with abnormalities in D-dimer plasma levels, and if so, whether such levels are related to the anticoagulation level and/or whether they could be predictive of acute vascular or hemorrhagic events. In 132 patients with single and 10 with double mechanical valve replacement, international normalized ratio (INR) and D-dimer plasma levels were determined. The INR levels of the previous 8 months were reviewed to assess the time that each patient spent in the therapeutic range. The D-dimer plasma levels were compared with those obtained from 102 matched control subjects. The patients were then followed up for 2 years to record acute vascular and hemorrhagic events. For the entire group, D-dimer plasma levels in patients were the same as those in the control group. Patients with double valve replacement had higher D-dimer plasma levels than either monovalvular implant patients or control subjects. Patients who had spent < 75% of the time within the assigned anticoagulation range had higher values for D-dimer plasma levels (median, 270 vs 198 ng/mL, P = .02). The major determinants of D-dimer plasma levels were age (R2 = .07, P = .009) and the percentage of time spent below the predetermined INR level (R2 = .09, P = .001). During follow-up, 19 acute vascular and 16 hemorrhagic events occurred. High D-dimer tertile was the only parameter predicting the occurrence of thromboembolic events. In patients with mechanical heart valve prostheses, the D-dimer plasma level depended on the thoroughness of anticoagulation. Patients in the upper tertile of D-dimer values have an approximately 5-fold risk of vascular thromboembolic events. D-dimer determination can therefore be useful in detecting patients who are at a higher risk of severe vascular events.

Adult↗

PubMed2005

The optimal method for recording prosthetic heart valve sounds in clinical situations.

BACKGROUND: Valve sounds are thought to be useful in evaluating the functioning of prosthetic heart valves. In previous reports, two recording instruments have mainly been used, a condenser microphone (instrument A) and an accelerometer (instrument B), respectively. This study aimed to investigate the applicability of these conventional devices in recording mechanical heart valve sounds in daily clinical situations. In addition, two other instruments, namely, a stethoscope including a small microphone in its tube (instrument C) and an electrostethoscope (instrument D), were proposed and examined. METHODS: Mechanical valve sounds were recorded from postoperative patients using each-device and the signal to noise ratio (SNR) of each was calculated. Frequency characteristics of the two newly proposed instruments were also investigated by recording a sweep signal in an anechoic chamber. RESULTS: The SNR values of the new instruments were significantly superior to those of conventional ones (A, sound signals were not defined from noises; B, 0.97 +/- 0.59 dB; C, 11.5 +/- 4.7 dB; and D, 9.4 +/- 3.5 dB, respectively p<0.05). The frequency characteristics of the two newly proposed instruments were also shown to be acceptable (under 10 kHz), though resonance frequency peaks were observed. CONCLUSIONS: Two newly proposed instruments can record mechanical heart valve sounds more noiselessly and with more ease than previous ones, and their frequency characteristics are acceptable.

Acoustics↗

PubMed1988

Mitroflow heart valve: 5.5 years clinical experience.

From March 1982 through December 1986, 139 Mitroflow pericardial heart valves were utilized in 129 patients. There were 69 males and 60 females, with an average age of 55.2, range 26 to 74 years. Eighty-nine patients underwent isolated aortic valve replacements, 27 isolated mitral valve replacements, 3 isolated tricuspid valve replacements, 10 mitro-aortic valve replacements. In 27 cases (20.9%) additional cardiac surgery was performed. Maximum follow-up was 5.5 years with a mean of 37.9 months. The cumulative follow-up was 407.25 patient-years. Overall hospital mortality was 1.6% (2 cases). There were 3 late deaths in this series (2.4%). The linearized incidence of late mortality was 0.49% per patient-year. The survival actuarial curve was 96% +/- 1.8. The incidence of thromboembolism was 1.22% per patient-year, and the actuarial thromboembolism-free rates was 93% +/- 2.7. Prosthetic endocarditis occurred in one patient. Three patients developed primary tissue failure of the Mitroflow valve in the mitral position. The linearized incidence of primary tissue failure was 0.73% per patient-year and the actuarial freedom from primary tissue failure was 95% +/- 3.2. A total of 4 patients underwent reoperation (0.49% per patient-year). In conclusion, the clinical performance of the Mitroflow pericardial heart valve at medium-term follow-up is satisfactory, however a significant number of early mitral primary tissue failures have already occurred.

Adult↗

PubMed2001

In vitro modelling of tissue using isolated vascular cells on a synthetic collagen matrix as a substitute for heart valves.

BACKGROUND: Tissue engineering is a promising approach for obtaining lifetime durability in biological heart valves. Basic questions with respect to the selection of suitable cell populations as well as scaffolds remain unsolved. The purpose of this study was to develop a tissue-like substitute in vitro for replacement of diseased valves in vivo. METHODS: Smooth-muscle cells (SMCs) were isolated from human and porcine aortic tissue using the 'explant technique' and endothelial cells from collagenase digestion. Seeding and cultivation of isolated cells was performed on a type-I collagen matrix. The scaffold-cell specimen was investigated using light and electron microscopy. Cupromeronic blue and immunoprecipitation were used for ultracytochemical staining. RESULTS: SMCs were allowed to grow to multilayers and migrate into the collagen network. We found a tissue-like morphology in these samples characterised by several layers of cells, spaces between the cell layers filled with newly formed extracellular matrix components, compartmentalisation of proteoglycans and their association with fibrilar matrix and the cell surface. Endothelium cells covered the SMCs of the scaffold with a histological topography similar to heart valves. CONCLUSIONS: This is an approach for in vitro modelling of tissue-like substitutes and preparing plane multicellular tissues as substitutes for heart valves. This model may also be used for cell biological investigations of cell-matrix interactions.

Animals↗

PubMed2001

International normalized ratio self-management after mechanical heart valve replacement: is an early start advantageous?

BACKGROUND: Severe thromboembolic and hemorrhagic complications after mechanical heart valve replacement essentially depend on the intensity of oral anticoagulation and the fluctuation of individual international normalized ratio (INR) values. METHODS: After heart valve replacement with Medtronic Hall, St. Jude Medical, and CarboMedics implants, patients were randomly divided into two groups, one controlling INR values at home, the other being monitored by family practitioners. RESULTS: Almost 80% of the INR values recorded by patients at home were within the stipulated therapeutic range, INR 2.5 to 4.5, compared with just 62% of INR values recorded by family practitioners. The overall complication rate (hemorrhages and thromboembolic events) of the self-management group was significantly (p < 0.05) decreased compared with the conventional group. CONCLUSIONS: Through INR self-management, an improvement in the quality of ongoing oral anticoagulation could be shown. Starting this form of therapeutic control early after mechanical heart valve replacement appears to effect a further reduction in anticoagulant-induced complications.

Adult↗

PubMedDate not supplied

Hydrodynamics of a long-body bileaflet mechanical heart valve.

A new bileaflet substitute mechanical heart valve (MHV) that incorporates an optimal length-to-annulus ratio for improved hydrodynamic efficiency was recently introduced. Efforts have been made on this new prosthesis to use the current advances in carbon materials and design technology to achieve higher net forward flow with minimal energy loss for the smaller aortic valves, while reducing regurgitant closure volume for the larger size valves by an elongated orifice. Benchtop experiments performed in a pulsatile flow loop, under simulated physiologic conditions, substantiated these improvements as claimed.

Aortic Valve↗

PubMed2001

[Model fluids of blood for in vitro testing of artificial heart valves].

The increasing development and implantation of artificial organs subject to perfusion with human blood once implanted (grafts, heart-valve prostheses and assist systems) require extensive testing of hydrodynamic performance in mock circulation models. As human blood ist not always available in the necessary quantities, different fluids (water, saline or glycerine solutions) are employed for measurements of flow characteristics. However, these model fluids do not possess the non-Newtonian rheological properties of blood. In addition, they do not allow estimation of possible blood damage. Aqueous solutions of high molecular weight polyacrylamides (PAA) have rheological properties similar to blood, displaying also molecular degradation due to shear stress in the flow. Therefore, they were used as model fluid for blood. Different model solutions were compared to blood with regard to their influence on characteristic flow parameters of mechanical heart valves. Likewise, the shear damage of erythrocytes could be compared to flow-induced polymer degradation. It was shown that PAA solutions in definite concentrations are suitable models for blood, not only in terms of non-Newtonian rheology, but also in terms of estimation of hemolytic potential of artificial heart valves.

Acrylic Resins↗

PubMed1999

[Progress in studies on cavitation of mechanical heart valve].

This paper reviews the researches on cavitation of mechanical heart valve in recent years and presents a discussion on the research methods. The achievements are summarized and the prospects of further research on cavitation in mechanical heart valve are brought forth.

Heart Valve Prosthesis↗

PubMed1987

Prevention of leaflet calcification of bioprosthetic heart valves with diphosphonate injection therapy. Experimental studies of optimal dosages and therapeutic durations.

Ethanehydroxydiphosphonate therapy was studied for prevention of calcification of bioprosthetic heart valve cusps (from glutaraldehyde-preserved porcine aortic valves) implanted subcutaneously in 3-week-old male rats. Animals received daily subcutaneous injections of the drug (1, 5, 10, 15, or 25 mg/kg/24 hr) for 21 days with maximal inhibition of bioprosthetic heart valve calcification at a dosage of 15 mg/kg/24 hr (calcium level of diphosphonate-treated bioprostheses 3.5 +/- 0.5 micrograms/ml; calcium level of control bioprostheses, 161.2 +/- 5.0 micrograms/mg), but with irreversibly diminished bone and somatic growth. A dosage optimum was observed at 10 mg/kg/24 hr with significant inhibition of bioprosthetic heart valve calcification (at 21 days, the calcium level was 16.4 +/- 3.6 micrograms/mg) and an absence of adverse effects on epiphyseal development and overall growth. Bioprosthetic heart valves retrieved from animal receiving ethanehydroxydiphosphonate (15 mg/kg/24 hr) for only the first week after implantation had significantly more calcification after 21 days than did bioprostheses from animals treated for 2 or 3 weeks. Bioprostheses explanted after 110 days from animals receiving the drug (15 mg/kg/24 hr) for the first 3 weeks had calcification equivalent to that of untreated control rats. Diphosphonate (15 mg/kg/24 hr) was most efficacious when initiated within 48 hours of bioprosthesis implantation, but was totally ineffective if administered after 1 week. It is concluded that ethanehydroxydiphosphonate optimally prevents bioprosthesis calcification without significant adverse effects on epiphyseal development and overall somatic growth at a dosage of 10 mg/kg/24 hr in rat subdermal implants, but it must be administered by continuous daily injections beginning within 48 hours of the implantation; this approach should be pursued in further long-term circulatory experimental studies because of its possible clinical relevance.

Animals↗

PubMed1999

[Prevention of prosthetic heart valve infection].

Fourty patients with primary and secondary infective endocarditis of the native heart valves as well as patients with rheumatic heart diseases not complicated by infective endocarditis were operated upon in the clinic from 1996 till 1998. The prosthetic heart valves in which the tissue cuff was sutures by blanket suture along the perimeter with a silver thread were implanted to 25 patients. In the other 15 patients (a control group) prosthetics were made using unchanged construction of the prosthesis (without the silver thread). Patients with valve prostheses sutured with the silver thread had smooth postoperative period. They had no prosthetic endocarditis either at the early or at late postoperative periods. In 3 patients of the control group infective endocarditis of the valve prosthesis developed at different periods after operation. All of them were reoperated. The authors consider that defense of the tissue cuff of the prosthetic valve with the silver thread allows risk of the development of prosthetic endocarditis to be substantially reduced. In the cases described it was completely avoided.

Adolescent↗