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PubMed2002

Physicochemical and microscopical study of calcific deposits from natural and bioprosthetic heart valves. Comparison and implications for mineralization mechanism.

Natural and bioprosthetic heart valves suffer from calcification, despite their differences in etiology and tissue material. The mechanism of developing calcific deposits in valve tissue is still not elucidated. The calcific deposits developed on human natural and bioprosthetic heart valves have been investigated and compared by physicochemical studies and microscopy investigations and the results were correlated with possible mechanisms of mineral crystal growth. Deposits from 16 surgically excised calcified valves (seven natural aortic and nine bioprosthetic porcine aortic valves) were examined by chemical analysis, FTIR, XRD, and SEM-EDS. The Ca/P molar ratio of the deposits from bioprosthetic valves (1.52+/-0.06) was significantly lower compared to that of the natural valves (1.83+/-0.03) (p=0.05, 1-way ANOVA). SEM-EDS examination of the two types of valve deposits revealed the coexistence of large (>20 microm) and medium (5-20 microm) plate-like crystals as well as microcrystalline (<5 microm) calcium phosphate mineral formations. The results confirmed the hypothesis that the mineral salt of calcified valves is a mixture of calcium phosphate phases such as dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP) and hydroxyapatite (HAP). DCPD and OCP are suggested to be precursor phases transformed to HAP by hydrolysis. The lower value of the Ca/P molar ratio found in the bioprostheses, in comparison with that corresponding in natural valves, was ascribed to the higher content in these deposits in precursor phases DCPD and OCP which were subsequently transformed into HAP. On the basis of chemical composition of the deposits and their morphology it is suggested that crystal growth proceeds in both types of valves by the same mechanism (hydrolysis of precursor phases to HAP) in spite of their differences in etiology, material, and possible initiation pathways.

Journal Article↗

PubMed1990

Laser assessment of leaflet closing motion in prosthetic heart valves.

The dynamics of leaflet motion in heart valve prostheses (HVP), and in particular the closing velocity, is believed to be related to the valve sound and possibly to the phenomenon of valve cavitation. This paper describes a non-intrusive laser sweeping technique enabling the study of leaflet motion. The principle of measurement and the equipment involved are presented, together with the results of two commercially available, 29 mm bileaflet mitral valves, a St. Jude Medical, and an Edwards Duromedic valve. Experiments were carried out in a pulsatile mock flow testing loop designed to mimic physiological pressure waveforms and ventricular contraction. Measurements of heart rate were made in the range 70-120 beats min-1, with a ventricular pressure slope range of 1800-5600 mm Hgs-1 and a cardiac output range of 5.0-7.5 litres min-1. Motion analysis of the measured data focuses on the velocity of the leaflet immediately before closure.

Equipment Design↗

PubMed1999

In vitro studies of gas bubble formation by mechanical heart valves.

BACKGROUND AND AIM OF THE STUDY: Recent clinical research using transcranial Doppler ultrasonography has shown the presence of emboli in the cranial circulation of some mechanical heart valve patients. Due to the high-intensity signals produced by these emboli, it has been suggested that they are small gas bubbles. Meanwhile, transesophageal echocardiography of mechanical heart valve patients has shown images of bright, mobile particles (also considered to be gas bubbles) near the valve. Motivated by these reports, a series of in vitro studies was performed to investigate the relationship between dissolved gas concentration and the incidence of bubble formation after valve closure. METHODS: A mock circulatory loop was used to study a Medtronic Hall tilting disc valve in the mitral position of the Penn State Electrical Ventricular Assist Device (EVAD). The valve was videotaped as it operated in saline with various levels of dissolved CO2. A Doppler ultrasound probe served as a bubble detector on the outflow side of the EVAD. Measurements of vaporous cavitation intensity with a high-fidelity pressure transducer were also made. Similar experiments were then performed in porcine blood, using an imaging ultrasound transducer to detect bubbles. RESULTS: Bubbles were seen moving off the valve in the retrograde direction just after closure. The ultrasound probe detected these bubbles downstream, indicating a bubble lifetime on the order of seconds. It was observed with high-speed video that bubble formation and cavitation are separate events and occur at different times during valve closure. Bubbles were more likely to be observed when CO2 levels were higher. Experiments in blood provided images of bubbles near the valve, predominantly at higher CO2 levels and high valve loading conditions. CONCLUSIONS: These results show that stable gas bubbles can form during mechanical heart valve operation. The bubbles likely form from the combined effects of gaseous nuclei formed by cavitation, low-pressure regions associated with regurgitant flow, and the presence of CO2, a highly soluble gas.

Animals↗

PubMed1996

Theory of wear as related to the Björk-Shiley Delrin disc heart valve.

BACKGROUND AND AIMS OF THE STUDY: Mechanical wear is an important consideration for the Björk-Shiley Delrin (BSD) heart valve, the disc of which is periodically impacted against the inlet strut by the momentum of the blood flow during closure. Impact wear theory was used in designing experiments as well as establishing theoretical evaluation and projections of wear life. MATERIALS AND METHODS: The experimental apparatus involved a pivotal hammer device where the striking face could be varied by the inclusion of distinct spherical shapes; the sharper the radius, the higher the contact stress induced. The striking speed could be varied between one and three m/s, and the repetition rate between 2-50 Hz. Blood was simulated with an aqueous 42% glycerol solution. The same wear mechanism was induced on Delrin occluder disc specimens as the one governing the wear observed in Delrin occluder discs of some of the explanted BSD heart valves; thus two wear parameters, c and g, were established for the prediction of wear in BSD implants. The experimental runs were repeated on as many as four simultaneous specimens, for up to 7.5 x 10(7) cycles. RESULTS: The wear history was found to comprise three distinct regions, corresponding to (a) initial plastic deformations; (b) zero wear; and (c) measurable wear. The zero wear region produced very little change in the contact dimensions, and represented a fatigue threshold to the progress of a wear scar. Procedures for analytical establishment of the zero wear limit are outlined in the paper. Measurable wear was governed by the process of increasing conformance between the repetitively contacting surfaces. The differential equation of wear was then used with the physical parameters c and g previously determined experimentally. CONCLUSION: The maximum depth of the wear scar after cycling the equivalent of 20 years was predicted to be 278 microns. This value appears to represent a safe dimension for BSD heart valves.

Biocompatible Materials↗

PubMed1980

[Sinus rhythm restoration in atrial fibrillation after heart valve prosthesis in rheumatic defects].

The rehabilitation program for patients who underwent heart valve prosthetics must include restoration of the sinus rhythm. On the basis of the results of electric-pulse therapy and quinidine therapy in 88 patients, it is shown that the first method is more effective than the second, but in view of the sufficient efficacy and safety of quinidine therapy with the use of medium daily doses (not more than 2 g) it may be used in some of the patients. It is advisable to restore the sinus rhythm in periods of 3 months to 3 years after operation on the heart. Restoration of the sinus rhythm improves the general condition of patients after heart valve prosthetics, normalizes hemodynamics, increases the physical capacity for work considerably, and provides greater possibilities for the return of convalescents to their jobs.

Atrial Fibrillation↗

PubMed2006

NFATc1 expression in the developing heart valves is responsive to the RANKL pathway and is required for endocardial expression of cathepsin K.

NFATc1 is necessary for remodeling endocardial cushions into mature heart valve leaflets and is also an essential effector of receptor activator of NFkappaB ligand (RANKL) signaling required for transcriptional activation of bone matrix remodeling enzymes during osteoclast differentiation. Therefore, developing heart valves were examined to determine if NFATc1 functions in the RANKL pathway during leaflet remodeling. Key components of RANKL signal transduction including RANKL, its receptor RANK, and the downstream remodeling enzyme cathepsin K (Ctsk) are expressed in the heart during valve remodeling and colocalize with NFATc1 in developing valve endocardium. However, the absence of tartrate-resistant acid phosphatase (TRAP) activity and the lack of F4/80-positive macrophage lineage contribution to the remodeling valves demonstrate that certain aspects of osteoclast RANKL function are not shared during valve formation. Analysis of NFATc1-/- mouse embryos shows that NFATc1 is specifically required for endocardial expression of RANKL and Ctsk during valve formation. In addition, RANKL treatment augments expression of NFATc1 and Ctsk in embryonic heart cultures, and the RANKL-mediated increase in Ctsk expression is dependent on NFATc1. Together, these results support a role for RANKL signaling during heart valve development and suggest that valve leaflet morphogenesis involves NFATc1-dependent expression of remodeling enzymes including Ctsk.

Animals↗

PubMed1994

[Treatment of MSOF after heart valve replacement: an analysis of 53 cases].

We treated 53 patients with multiple system organ failure (MSOF) following heart valve replacement. MVR was performed in 20 cases, AVR in 6 and DVR in 27. Before operation, NYHA functional class II was in 5, III in 17, and IV in 31. MSOF of all 53 patients occurred within 2-7 days after operation, and failing organs involved heart, lungs, kidneys, brain, gastrointestinal and blood coagulation system. The patients with the maximum organ failure had 6 failing organs, 36 of the 53 patients were living and 17 (32.1%) died. The mortality correlated positively with the number of failing organs. The results of MSOF which occurred sequentially were better compared with those occurred simultaneously. The death rate in patients with class IV was higher than that in those class II, III. The type of operation (MVR, AVR, DVR) did not effect the result of MSOF. The causes and management of MSOF after heart valve replacement were discussed.

Adult↗

PubMed2001

Risks and benefits of adding anti-platelet therapy to warfarin among patients with prosthetic heart valves: a meta-analysis.

OBJECTIVES: The objective of this study was to compare the effectiveness and safety of adding dipyridamole or aspirin to warfarin among patients with prosthetic heart valves using meta-analytic techniques. 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. METHODS: A combined MEDLINE and manual search was made for relevant articles from 1966 to November 1999. Standard meta-analysis techniques were used. RESULTS: Ten studies involving 2,199 subjects met the inclusion criteria. Compared with anticoagulation alone, the addition of an antiplatelet agent reduced the risk of thromboembolic events (odds ratio [OR]: 0.41, p < 0.001) and total mortality (OR: 0.49, p < 0.001). The risk of major bleeding was increased when antiplatelet agents were added (OR: 1.50, p = 0.033). For major bleeding, the comparison of trials performed before and after 1990 (OR: 2.23 and 0.88, respectively) showed that the chi-square test for heterogeneity was significant (p = 0.025). The latter trials used low-dose aspirin, suggesting that the risk of bleeding may be lower with contemporary low-dose (100 mg daily) aspirin. CONCLUSIONS: Adding antiplatelet therapy, especially low-dose aspirin, to warfarin decreases the risk of systemic embolism or death among patients with prosthetic heart valves. The risk of major bleeding is slightly increased with antiplatelet therapy. Nonetheless, the risk of bleeding appears to have diminished with the lower doses of aspirin used in the more recent trials, resulting in a favorable risk-to-benefit profile.

Aspirin↗

PubMed2003

Bubble observation and transient pressure signals in mechanical heart valve cavitation study.

BACKGROUND AND AIMS OF THE STUDY: Cavitation in the mechanical heart valve (MHV) was first detected in Edwards-Duromedics (ED) clinical explants. Early studies indicated that the pitted surface of the valve leaflet was due to cavitation phenomena occurring during valve closing. Cavitation is seen as the transient appearance of bubbles on the MHV surface on valve closure. The cavitation bubbles occur due to abrupt pressure changes in the vicinity of the valve on valve closing. Hence, analysis of the recorded field pressure can provide useful information relating to cavitation potential. In the present study, MHV cavitation potential was evaluated by counting bubble appearance probability and measuring bubble-size using an image-processing method. A simple and reliable technique using wavelet packet analysis (WPA) to evaluate cavitation potential was also investigated. METHODS: A single-valve, pneumatic-driven burst tester system with adjustable pressure control unit, was used to simulate the closing process in the heart mitral valve at three driving pressures: 200, 500 and 1,000 mmHg, using three valve models. A triggering and imaging system was developed within the burst tester system to capture images of cavitation bubbles at predetermined time delays on valve closing. Transient pressure signals were recorded on both sides of the MHV occluder, using a high-frequency piezoelectric pressure transducer and a physiological pressure transducer. The pictures recorded were analyzed using image processing software to determine bubble appearance probability and bubble size. WPA was applied to the transient closing pressure signals to evaluate cavitation potential. RESULTS: Cavitation intensity index (Cii) and bubble size-based cavitation index (BS-Ci) were measured by analyzing images captured at different time delays on valve closing at different driving pressures. WPA was used to analyze transient pressure signals at the inflow side of the MHV occluder at valve closure to calculate the WPA-based cavitation index (WPA-Ci). The three methods showed a similar trend for cavitation potential in the valves tested. CONCLUSION: In the present study, two new approaches to evaluate MHV cavitation were investigated, namely WPA and BS-Ci. The results obtained produced a similar trend to that seen with an earlier method based on counting the probability that cavitation bubbles occur. As cavitation is primarily a function of the transient pressure within the vicinity of the closing valve occluder, the WPA method can be an effective method for future investigation of cavitation potential of mechanical heart valves.

Biophysical Phenomena↗

PubMed2004

[Implementation of habituation theory to pulsatile somato-sounds (tinnitus): the heart valve prosthesis sound model].

OBJECTIVES: To evaluate the habituation process to mechanical heart valve prosthesis sound as a model to understand the pulsatile tinnitus or somatosound perception changes. STUDY DESIGN: Transversal descriptive. PATIENTS: One hundred and fifty patients referred to a University Hospital for one or two mechanical heart valve implantation. OUTCOME MEASURES: Questionnaire sent by mail for prosthesis sound loudness and interference in quality of life evaluation. Detection of factors related to habituation process development. RESULTS: Eighty three percent of the patients perceived their prosthesis sound continuously, while only a 17% showed high levels of annoyance. No significative differences in prosthesis type and localization were described. Anxiety was the most important factor for loudness increase. The average of visual analogical scales on sound loudness and annoyance showed mild values (3.7 and 1.9 respectively). CONCLUSIONS: Extensive medical counselling or tinnitus retraining therapy (TRT) program for most severe cases, are proposed for pulsatile tinnitus management when etiological treatment cannot be available.

Adult↗

PubMed1992

Mechanical heart valve prostheses: sound level and related complaints.

In a randomised study, we investigated the sound production of mechanical heart valve prostheses and the complaints related to this sound. The CarboMedics, Björk-Shiley monostrut and StJude Medical prostheses were compared. A-weighted levels of the pulse-like sound produced by the prosthesis were measured in 25 patients after aortic valve replacement. Additionally, 141 patients, 117 after aortic valve replacement, 20 after mitral valve replacement and 4 after double valve replacement were interviewed. The average sound pulse pressure levels were 46.0 +/- 2.9 dB(A) in the Carbomedics group, 55.4 +/- 1.2 dB(A) in the Björk-Shiley monostrut group and 44.1 +/- 4.4 dB(A) in the StJude Medical group, measured at a distance of 1 cm from the chest. The Björk-Shiley monostrut was louder than the other two prostheses (p less than 0.0005). Twenty (14.2%) of all patients had complaints related to the valve sound such as sleeping disturbances, irritation, nervousness or fear. Significantly more patients with a Björk-Shiley monostrut could hear their valve or had complaints when compared to the other two prostheses. Younger patients and patients with a mitral valve prosthesis could hear their valve more often than older patients or patients after aortic valve replacement. We conclude that sound characteristics and related complaints differ considerably among heart valve prostheses.

Aged↗

PubMed1989

Actuarial analysis of a uniform and reliable preservation method for viable heart valve allografts.

CryoLife has developed a method for cryopreserving allograft heart valves for transplantation. Since 1984, 6,907 valves have been processed and 4,216 transplanted. Documentation was available on 2,647 transplants, 11 of which were removed for structural deterioration and 13, for nonstructural deterioration. At the end of 35 months, actuarial survival was 99.17% and the estimated freedom from reoperation, 97.16%. There have been no reports of thromboembolism or valve-related death.

Actuarial Analysis↗

PubMed1982

Bioengineering aspects of heart valve replacement.

Biomedical engineering inputs have been important in the design, development and testing of substitute heart valves as well as in the pre- and post-operative management of patients with cardiac valve disease. This paper is a review of heart valve replacement whose goal is the enhancement of future bioengineering contributions. We review the approach to the patient with valvular heart disease, and the sources of early and late postoperative pathology with emphasis on complications of the prostheses used. Major significant problem areas relate to the noninvasive evaluation of cardiovascular function (both before and after surgery), device design, hemodynamics, and the need for thromboresistant and durable materials.

Biomedical Engineering↗

PubMed2002

Effect of oral anticoagulant during pregnancy with prosthetic heart valve.

This retrospective study aimed to evaluate the risks and outcome of oral anticoagulant use during pregnancy in women with prosthetic heart valves. Between December 1989 and November 1998, 192 females of childbearing age underwent heart valve replacement with a mechanical prosthesis. There were 37 pregnancies in 30 patients during follow-up. Pregnancy was terminated on medical grounds in 5 cases, there were 2 (6%) spontaneous abortions, and 1 (3%) premature birth of a normal baby who died 24 hours later due to asphyxia. The other 29 pregnancies (91%) went to full term and the mothers continued taking oral anticoagulants until a week before the expected date of delivery, then switched to heparin. There was no thromboembolism, valve thrombosis, or maternal mortality. Three babies (10%) had a skeletal deformity: nasal hypoplasia in all 3, with cleft pinna in 1. Continuation of oral anticoagulants during pregnancy provided adequate protection against thromboembolism and valve thrombosis, but the risks of fetal abnormalities and premature delivery should be explained to women of childbearing age with a mechanical valve prosthesis.

Abnormalities, Drug-Induced↗

PubMed1987

[Heart valve replacement in patients over age 60: analysis of the peri- and postoperative course compared to patients under age 60].

During recent years, advances in cardiology and cardiac surgery have led to an increased number of older patients submitted for heart valve replacement. The following retrospective study analyses perioperative risk and long-term prognosis of 168 patients older than 60 years of age, compared with 942 patients younger than 60 years of age with heart valve replacement. There was no significant difference in 7-year actuarial survival, late mortality, late complications and postoperative functional improvement for both groups. However, early mortality was higher in patients over 60 years of age than in the group of patients under 60 years (7.9% vs. 4.5% from 1980-85, p less than 0.05), especially when multivalvular replacement was performed or the patients were in preoperative functional class NYHA IV. The results indicate that in patients over 60 years of age, heart valve replacement can be performed with a good long-term prognosis and a marked improvement in the quality of life. Early mortality can be reduced to an acceptable rate if the patient is operated in time.

Adolescent↗

PubMed1989

Dental procedures and endocarditis prophylaxis in patients with prosthetic heart valves: results of a questionnaire to 220 patients.

220 patients with prosthetic heart valves were surveyed regarding dental status, dental health, patient-dentist relationship, information on dental procedures and antimicrobial prophylaxis at the last visit to the dentist. The vast majority of these patients were on life-long anticoagulant treatment because of mechanical heart valve prostheses. Half of the patients had a regular dentist and customarily visited a dentist one or more times a year. One third of the patients were edentulous and 26.5% of the patients indicated dental disease, including chronic periodontitis. Only 30.4% of the patients received antimicrobial prophylaxis in connection with dental extraction and only 13.8% in connection with scaling. Maintenance of good oral health, routine dental checks and better information to the patients and the dentist are called for.

Adult↗

PubMed1989

[In vitro hemodynamic characteristics of prosthetic heart valves].

The functional characteristics of the prosthetic heart valve are the hemodynamic characteristics when it has been ideally attached; in clinical practice, however, it is seldom that this artificial valve is ideally put in position because of the modality of changeable valve angle in deformed annulus and the narrow aortic root, orientation of the valve, anatomical factors, etc. Thus, we devised an attachment head for the prosthetic valve whose angle can freely be varied in order to evaluate the hemodynamic characteristics of five clinically-available mechanical prosthetic valves and two xenografts in the pulsatile circulation system in the mitral position by changing the angle and orientation of the valve attachment. The prosthetic valves used were St Jude Medical (SJM), Starr-Edwards ball (S-E), monostrut Björk-Shiley (mB-S), Omniscience (OS), Omnicarbon (OC), Carpentier-Edwards Supra-annular (C-Es) and Carpentier Edwards Pericardial (C-Ep) whose tissue annulus diameter was 27 mm. The experimental instrument similar to that of Umezu et al. was prepared to determine the mean pressure gradient, output and calculated orifice area of each valve. At the same time, a recently-manufactured valve attachment head was employed to measure the output, pressure gradient and orifice area by altering the valve attachment angle and orientation and increasing the number of heart beats from 60 bpm to 160 bpm, and the following results were obtained: With the changeable angle valve, an angle was determined whose end was parallel to the flow path in association with changes in the attachment angle, and the orientation was such that the pressure gradient was reduced and the orifice area was increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioprosthesis↗

PubMed2003

Does the noise of mechanical heart valve prostheses affect quality of life as measured by the SF-36 questionnaire?

OBJECTIVE: The closure clicks of mechanical heart valve prostheses' leaflets are quite often clearly audible. The study describes the effects of subjective valve sound perception on the patients' quality of life and analyses factors that might contribute to valve noise-related discomfort. METHODS: We included 556 patients who received a mechanical valve prosthesis and participated in the study in our institution from 1994 to 1998. All compiled the standardised questionnaire Short-Form-36 Health Survey (SF-36) and indicated their subjective disturbance grade pre- and postoperatively, then every 6 months up to 2 years. A series of factors was scanned for correlation with unpleasant noise perception. RESULTS: Two years after the operation, only 5.8% classified their valve sounds as 'quite' or 'very much' disturbing. Age <60 years and being female were statistically significant factors for persisting unease caused by valve sounds. Without one of these factors, severe disturbance chance was 1.5%. As expected, quality of life improved after surgery. Patients disturbed seriously by valve noise showed significantly lower mean life quality values on each SF-36 scale. CONCLUSION: Patients (94.2%) with mechanical heart valve replacement have no persistent complaints about the valve noise. The grade of annoyance by valve noise is paralleled by lower average quality of life. Age under 60 years or being female increases the probability of severe disturbance due to mechanical valve sounds. It remains unclear whether the disturbing noise is reason or consequence of lower quality of life.

Adolescent↗