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PubMed1995

Dynamic characteristics of prosthetic heart valves.

The relation between flow rate (Q) and transvalvular pressure-drop (DP) is of fundamental importance for a prosthetic heart valve tested in steady flow conditions. The Q-DP plot can thus be called the static characteristic of the valve. While in pulsatile flow, with time (t) as a parameter, the instantaneous Q(t)-DP(t) relation can also be obtained. The Q-DP relation forms a phase graph on an X-Y plane during a whole cardiac cycle, and can be regarded as the dynamic characteristic, which to our knowledge has never been systematically explored before. With in vitro experiment the Q(t)-DP(t) relations are presented for five different aortic valves. Properly modelling the characteristics of heart valves is a key link in modelling the interactions between the ventricle and arterial system. Treatments for valves, such as diode analogue and orifice area assumption governed by the Gorlin formula, are found unsatisfactory. A simple one-dimensional flow equation is used to further examine the Q-DP graph, and both the dynamic resistance characteristic and the dynamic flow characteristic can be obtained. It is found that the dynamic characteristic differs from the static one not only in the inertance effect but also in the transient process, which can be quite energy-consuming and therefore important. Geometric relations of these phase graphs with the transvalvular power loss are discussed. The method of dynamic characteristics provides a new way to evaluate the performance of a tested valve.

Biomedical Engineering↗
PubMed1969

Isolation and properties of hyaluronic acid from bovine heart valves.

1. A soluble extract of bovine heart valves was obtained after the tissue had been pulverized at liquid-nitrogen temperatures in a mill. 2. Hyaluronic acid was isolated from the crude extract by sedimentation equilibrium in a caesium chloride density gradient (Franek & Dunstone, 1966). 3. Analysis of the product indicated that it contained 15% of protein and the molar ratio of glucuronic acid to glucosamine was 1.27. 4. Its physicochemical properties, as determined by lightscattering, viscosity and sedimentation studies, suggested that its molecular size and configuration were similar to those of hyaluronic acid isolated from ox synovial fluid (Preston, Davies & Ogston, 1965).

Animals↗
PubMed2000

Can vortices in the flow across mechanical heart valves contribute to cavitation?

Cavitation in mechanical heart valves is traditionally attributed to the hammer effect and to squeeze and clearance flow occurring at the moment of valve closure. In the present study, an additional factor is considered--the contribution of vortex flow. Using a computational fluid dynamics analysis of a 2D model of a tilting disk mitral valve, we demonstrate that vortices may form in the vicinity of the inflow side of the valve. These vortices roll up from shear layers emanating from the valve tips during regurgitation. A significant decrease in the pressure at the centre of the vortices is found. The contribution of the vortex to the total pressure drop at the instant of closure is of the order of 70 mmHg. Adding this figure to the other pressure drop sources that reach 670 mmHg, it might be that this is the deciding factor that causes the drop in blood pressure below vapour pressure. The total pressure drop near the upper tip (750 mmHg) is larger than near the lower tip (670 mmHg), indicating a preferential location for cavitation inception, in agreement with existing experimental findings.

Blood Flow Velocity↗
PubMed1975

[Heart valve surgery in bacterial endocarditis (author's transl)].

Bacterial endocarditis was the cause of heart valve destruction in 23 patients. Additional 5 patients were reoperated because of an infected valve prothesis. 13 were operated upon during the inactive stage. Nevertheless infection recurred after operation at least in one patient. 10 patients underwent operation during the active stage, 6 of these with stable cardiac function, 4 in cardiogenic shock. Hospital mortality was 2/6 and 1/4 respectively. One patient died after three months of persisting infection. Three of five patients with infected valve prosthesis survived reoperation. An attempt is made to define the indication for valve surgery in bacterial endocarditis.

Adolescent↗
PubMedDate not supplied

In vivo observation of cavitation on prosthetic heart valves.

In this study, a method to determine the existence of prosthetic heart valve cavitation in vivo is presented. Pennsylvania State University Left Ventricular Assist Devices (LVADs) were implanted in two separate calves for this study. Björk-Shiley Monostrut (Irvine, CA) 27 mm and 25 mm valves with Delrin occluders were used in the mitral and aortic positions, respectively. A high fidelity, piezoelectric pressure transducer was mounted approximately 1.25 cm proximal to the mitral valve and measured the high frequency pressure fluctuations caused by cavitation bubble formation and collapse after valve closure. The root mean square (RMS) value of the mitral pressure signal during a 5 ms interval after valve closure was used as a measure of cavitation intensity. The pressure signals observed in vivo were similar to ones observed in vitro with the same type of pressure transducer and were associated with the visually observed cavitation. The percentage of beats with cavitation increased from 20.3% to 67.7% when pump filling was decreased by increasing beat rate. A blood test conducted during post-operative days 1-3 showed a significant increase in plasma hemoglobin during the low filling condition. However, blood tests conducted later (post-operative days 7-44) did not show a significant change in plasma hemoglobin during low filling conditions.

Animals↗
PubMed1993

Age thresholds for prophylactic replacement of Björk-Shiley convexo-concave heart valves. A clinical and economic evaluation.

BACKGROUND: Björk-Shiley convexo-concave heart valves have an increased risk of mechanical failure. One might consider prophylactic rereplacement as a preventive measure to avert the disastrous consequences of these failures. We investigated the effect that prophylactic rereplacement has on survival of individual patients and on the medical costs. METHODS AND RESULTS: Quantitative estimates for the surgical risks of prophylactic replacement of Björk-Shiley valves, long-term survival, and the risk of outlet strut fracture were derived insofar as possible from a detailed analysis of a follow-up study conducted in The Netherlands, including 2303 patients with a mean follow-up of 6.6 years. On the basis of these estimates, we calculated life expectancy with and without prophylactic replacement. For the various valve types, age thresholds were determined below which rereplacement prolongs (discounted quality-adjusted) life expectancy. We also calculated the cost per year of life gained as a function of age. The age thresholds below which prophylactic rereplacement increases life expectancy (expressed in simple future years of life) for male patients without comorbidity, if the surgical mortality after rereplacement is equivalent to that of primary replacement, are 27, 48, 51, and 65 years for small and large 60 degrees and for small and large 70 degrees mitral valves, respectively. For aortic valves, these age thresholds lie somewhat higher: 39, 52, 56, and 76 years, respectively. Repeat analyses indicated that for women, all age thresholds lie about 1 or 2 years higher. These age thresholds decrease considerably if the surgical mortality after rereplacement is considered to be higher after prophylactic rereplacement than after primary replacement or if comorbidity is present. The costs per discounted and quality-adjusted year of life gained depend on type and position of the Björk-Shiley convexo-concave heart valve and rise steeply as the patient's age approaches the threshold for rereplacement. CONCLUSIONS: The results of the Dutch follow-up study allow guidance for prophylactic replacement of the Björk-Shiley convexo-concave valve on an individual basis. Rereplacement compares favorably with expectant management in some patient subgroups with both 60 degrees and 70 degrees valves. Age thresholds may serve as a first step in identifying patients in whom rereplacement might be beneficial.

Adult↗
PubMedDate not supplied

Venturi pressure cannot cause cavitation in mechanical heart valve prostheses.

Surface pitting of certain mechanical heart valve (MHV) explants has prompted investigation into possible causes of cavitation during MHV operation. Leaflets of a 29 mm MHV were glued shut with B-datum (BD) gaps fixed at 0.0089, 0.0174, and 0.0219 cm. Each BD gap setting was tested in a steady flow chamber, with leakage flow established at transvalvular pressures (delta P) of 20 to 200 mmHg. Laser Doppler velocimeter (LDV) velocity measurements were recorded 220 microns distal to the BD, along with leakage flowrates. Maximum LDV velocities were compared with those calculated using the mass conservation equation. At identical P, the LDV flow velocities for the three BD settings were found to be approximately equal. This indicates a geometric independence of the leakage flow velocity. At atmospheric pressure, the local velocity necessary to cavitate blood as a liquid is approximately 13 m/sec. These results demonstrate that the leakage velocity is insufficient to cause cavitation. A simplified theoretical model is proposed to illustrate the necessary delta P to produce Venturi related cavitation.

Blood Flow Velocity↗
PubMedDate not supplied

A non-conventional reniform heart valve bioprosthesis with improved performance.

Conventional bioprosthetic heart valves have been designed with circular mounting rings. This article describes a mitral bioprosthetic valve consisting of three bovine pericardial leaflets with a "reniform" base. Its shape resembles that of the mitral anulus, and therefore, it provides a better anatomic fit. Hydrodynamic comparisons were made between conventional valves (CV) and equivalent sized reniform valves (ERV) that would adapt to the same anulus. Under steady flow of 30 L/min, pressure drops were compared in CVs and ERVs. For CV sizes 27, 29, and 31mm, the ratios of pressure drops compared with ERVs were 2, 1.49, and 1.30, respectively. With the same flow rate, the ratios of effective orifice areas (EOA) for CVs and ERVs in sizes 27, 29, and 31mm were 1.41, 1.21, and 1.14, respectively. Under pulsatile flow (mean flow, 5 L/min, 100 beats/min [bpm]), the pressure drop across CVs was averaged for sizes 27, 29, and 31mm, and found to be 1.51-fold the averaged pressure drops for ERVs. In addition, ERV sizes 27, 29, and 31mm had EOAs averaging 1.24-fold those of CVs. Similarly, for an 80 bpm frequency, the pressure drops across CVs for the three sizes averaged 1.48-fold that of ERVs. The EOAs of ERVs were 1.22-fold those of CVs averaged for the three sizes.

Animals↗
PubMed1976

The course of pregnancy in patients with artificial heart valves.

Twenty-five women with prosthetic heart valves (PHV) became pregnant 28 times. Twenty-six of the pregnancies occurred while the patients were receiving oral anticoagulants and these were continued throughout in 25 pregnancies. Dipyridamole or dipyridamole and acetylsalicyclic acid were used in 22 pregnancies. Eighteen infants were delivered, one with a congenital corneal leukoma; none had hemorrhagic complications; their psychomotor development was normal. Nine women aborted 10 times, including patients with two PHV, pelvic trauma and self-induced abortion. We could not detect excess anticoagulation in eight of the nine who had spontaneous losses; excess anticoagulation occurred five weeks before an abortion. There were no maternal deaths despite numerous complications; in two women, brain embolism was related to short interruptions of anticoagulation. The details of management are mentioned. We lack enough evidence to suggest routine sterilization, routine interruption of coumarin therapy during pregnancy or routine interruption of pregnancy in women with certain types and models of PHV; however, pregnancy under such conditions, plus antithrombotic therapy, carries a high risk for the product and a potential teratogenic effect. Women with one or two PHV can have children if their management is closely supervised and if extreme care is taken with the use of oral anticoagulants.

Abortion, Spontaneous↗
PubMed2001

Differences in heart valve procedures between North American and European centers: a report from the Artificial Valve Endocarditis Reduction Trial (AVERT).

BACKGROUND AND AIM OF THE STUDY: Differences in heart valve procedures between North American (NA) and European (EU) centers were evaluated in a multicenter trial. METHODS: Between July 1998 and January 2000, 807 patients from 12 NA (n = 446) and seven EU centers (n = 361) were randomized to receive either Silzone or conventional valves in the Artificial Valve Endocarditis Reduction Trial (AVERT). Subanalysis was performed to compare demographics, patient risk profile, surgical techniques and perioperative management of patients in NA and EU centers. RESULTS: Mean age was significantly younger and body mass index higher in NA. Patients' risk profiles showed significantly higher incidences of previous myocardial infarction, congestive heart failure, angina, prior cardiovascular surgery, and history of smoking in NA. A different distribution of implant position was observed between groups: aortic valve/mitral valve/double valve replacement in 54.0, 35.7 and 10.3% in NA, and 64.5, 27.4 and 8.0% in EU (p <0.01). Concomitant coronary artery bypass grafting was performed in 31.6% of NA patients and 19.4% of EU patients (p <0.001). Timing of surgery showed a higher incidence of urgent procedures in NA centers. Distribution of valve sizes and perioperative complication rate were similar, but length of hospital stay was longer in EU centers. CONCLUSION: Surprisingly, surgeons in NA and EU centers are faced by different patient populations requiring mechanical heart valve replacement. NA patients were younger, but required more extensive surgery. Surgical technique and perioperative management appear to differ in NA and EU centers. These differences in reporting heart valve procedures might have been influenced by variable interpretations of definitions and different patient expectations, although a uniform study protocol with consistent definitions was used at all sites.

Aged↗
PubMed2002

In-vitro and in-vivo activity of antimicrobial-coated prosthetic heart valve sewing cuffs.

BACKGROUND AND AIM OF THE STUDY: Prosthetic valve endocarditis (PVE) is a relatively uncommon but very serious condition. As bacterial colonization of the prosthetic heart valve sewing cuff can be a prelude to the clinical occurrence of PVE, antimicrobial coating of the sewing cuff may be beneficial. The study aims were to examine the antimicrobial activity in vitro and anti-infective efficacy in vivo of prosthetic heart valve sewing cuffs coated with minocycline and rifampin. METHODS: Zones of inhibition by antimicrobial-coated sewing cuffs were assessed in vitro against Staphylococcus epidermidis, S. aureus, Enterococcus faecalis, Pseudomonas aeruginosa and Candida albicans. The ability of subcutaneously implanted devices coated with minocycline and rifampin to resist colonization and infection by P. aeruginosa was also examined in a rabbit model. RESULTS: Antimicrobial-coated sewing cuffs produced zones of inhibition against all tested organisms. Coated devices were significantly less likely than uncoated devices to become colonized (2/24; 8% versus 20/24; 83%; p <0.001) or to cause device-related infection (0/24; 0% versus 18/24; 75%; p <0.001) and device-related abscess (0/24; 0% versus 10/24; 42%; p <0.001) due to P. aeruginosa. CONCLUSION: Prosthetic heart valve sewing cuffs coated with minocycline and rifampin provide broad-spectrum antimicrobial activity in vitro, and are anti-infective in vivo against P. aeruginosa. These results encourage the clinical evaluation of these sewing cuffs.

Animals↗
PubMed1996

Mechanical performance of pyrolytic carbon in prosthetic heart valve applications.

An experimental procedure has been developed for rigorous characterization of the fracture resistance and fatigue crack extension in pyrolytic carbon for prosthetic heart valve application. Experiments were conducted under sustained and cyclic loading in a simulated biological environment using Carbomedics Pyrolite carbon. While the material was shown to have modest fracture toughness, it exhibited excellent resistance to subcritical crack growth. The crack growth kinetics in pyrolytic carbon were formulated using a phenomenological description. A fatigue threshold was observed below which the crack growth rate diminishes. A damage tolerance concept based on fracture mechanics was used to develop an engineering design approach for mechanical heart valve prostheses. In particular, a new quantity, referred to as the safe-life index, was introduced to assess the design adequacy against subcritical crack growth in brittle materials. In addition, a weakest-link statistical description of the fracture strength is provided and used in the design of component proof-tests. It is shown that the structural reliability of mechanical heart valves can be assured by combining effective flaw detection and manufacturing quality control with adequate damage tolerance design.

Biocompatible Materials↗
PubMed2006

[Reoperation about recurrent heart valve disease in 221 cases].

OBJECTIVE: To retrospectively review the experience of reoperation after closed mitral commissurotomy, valvuloplasty, perivalvular leakage and dysfunction of bioprosthetic valve in 221 cases. METHODS: Two hundred and twenty-one patients underwent heart valve reoperation from January 1998 to August 2005. Among them, 8 cases was emergency operation. The reasons of reoperation included 105 cases suffered from mitral valve restenosis after closed mitral commisurotomy, 37 cases suffered from valve lesion after mitral or aortic valvuloplasty, 29 cases suffered from perivalvular leakage after valve replacement. Eighteen cases suffered from bioprosthetic valve decline, 9 cases suffered from dysfunction of machine valve, 7 cases suffered from tricuspid insufficiency of Ebstein, 5 cases suffered from prosthetic valve endocarditis and 11 cases suffered from other valve disease. The re-operations were mitral valve replacement, mitral and aortic valve replacement, aortic valve replacement and tricuspid valve replacement. The interval from first operation to next operation was 1 - 21 years. RESULTS: The early-stage postoperative mortality was 8.6% (19/221). And the reasons were low cardiac output syndrome, arrhythmia, multiple organ dysfunction failure (MODF) and renal failure. Among these the emergency operative mortality was 3/8. And the mortality was 14.5% (9/62) in class IV of cardiac function (NYHA). CONCLUSIONS: The risk factors of reoperation about heart valve disease include emergency operation, low preoperative cardiac function, MODF, long time of cardiopulmonary bypass and aortic blocking. Therefore it is emphasized that mastering and treating the risk factors promptly, which could decrease the mortality and incidence of complication.

Adolescent↗
PubMed1989

[The effect of intravascular hemolysis on the body of rheumatics with heart valve prostheses].

The rate of intravascular hemolysis and associated complications was studied in 100 patients with rheumatic heart disease within 2 to 20 years after replacement of the heart valves. Hemolysis of varying intensity was recorded in 72% of patients, anemia in 5%, hemosiderinuria in 27%, cholelithiasis in 4%, and sideropenia in 36.8% of the examined. Renal failure was diagnosed in none of the patients. Thromboembolic complications were more frequently encountered in patients with hemolysis. In order to prevent anemia and sideropenia, it is recommended that control may be exercised over hemolysis and iron content in the blood of patients with prosthetic heart valves.

Anemia, Hemolytic↗
PubMed2003

Reduction of mechanical heart valve thrombosis through a clinical audit.

BACKGROUND AND AIM OF THE STUDY: Patients with mechanical heart valves implanted at four cardiothoracic centers were followed up in a hospital in Eastern India. Despite successful surgery and regular hospital visits, long-term survival was compromised by anticoagulation-related complications. METHODS: Systematic analysis revealed under-anticoagulation in most patients. Thrombosis risk in 80 patients on regular follow up from 1989 to 1997 was 8.68 per 100 patient years (pt-yr). The incidence of both thrombotic and bleeding complications was reported as less than two per 100 pt-yr, when prothrombin time was consistently in the range of INR 2.5 to 3.9. In targeting this low event rate, impediments to optimum anticoagulation in the local set-up were identified. International Normalized Ratio (INR) was introduced to report prothrombin time (PT). Patients and doctors were educated about drug and diet interactions with oral anticoagulants (OAC) and the early features of valve thrombosis. Treatment protocols were evolved. The impact of the remedial measures was studied in 81 patients (64 old, 17 new) over a total of 254 pt-yr of follow up, from 1998 to 2001. RESULTS: Thrombosis risk was reduced from 8.68 to 5.12 per 100 pt-yr, while non-fatal bleeding events increased from 0.28 to 1.96 per 100 pt-yr. Due to early recognition of occlusive prosthetic valve thrombosis and institution of fibrinolytic therapy, fatal events were reduced from 3.8 per 100 pt-yr to none for four consecutive years (statistically significant at 99% CI). CONCLUSION: The clinical audit proved to be a valuable tool for understanding the problems in health care delivery, and bringing about improvement.

Administration, Oral↗
PubMed1982

Calcification of porcine prosthetic heart valves: a radiographic and light microscopy study.

To determine the incidence and extent of calcification of implanted glutaraldehyde-treated porcine prosthetic heart valves, 82 valves explanted from 73 patients were examined for calcium by radiography and light microscopy. At the time of valve implantation, the patients were 2 1/4-76 years old. The included 15 children (patients younger than 15 years of age, mean age at time of valve implantation 8.7 +/- 4.1 years) and 58 adults (patients older than 15 years, mean age at time of valve implantation 53.5 +/- 15.1 years). Valves explanted from children (average time implanted 4.6 +/- 1.7 years) included four aortic, five mitral, as well as six right ventricle-pulmonary artery conduits and one left ventricle-abdominal aorta conduit. Valves explanted from adults (average time implanted 3.2 +/- 2.5 years) included 32 aortic and 32 mitral, as well as one tricuspid valve and one valve from a right ventricle-pulmonary artery conduit. Calcification of explanted valves was graded from 0 to 4+ based on radiographs. All 16 valves from children were calcified, with grade 3+ or 4+ calcification in each of the aortic and mitral valves. In adult patients, calcification was present in 10 of 33 valves (30%) implanted for less than 3 years (average time implanted 1.0 year), in nine of 11 valves (82%) implanted for 3-5 years (average time implanted 3.7 years) and in 21 of 22 valves (96%) implanted for 5 years or longer (average time implanted 6.2 years). Analysis of variance demonstrated that calcification was strongly related to the duration that valves were implanted (p less than 0.001). Age at the time of valve implantation also had a strong effect (p less than 0.001) on the amount of valvular calcium. Valves from children showed the most calcification, and the amount did not change when valves were implanted in patients 30 years of age or older. Patient sex and valve position had no effect on the amount of calcification. Calcification occurred at each right- and left-heart valve position, most frequently at sites of commissural attachments.

Adolescent↗