In vitro comparison of steady and pulsatile flow characteristics of jellyfish heart valve

In examining the hydrodynamic performance of artificial heart valves in vitro, experiments are carried out under either steady or pulsatile flow conditions. Steady flow experiments are simple to set up and analysis of the data is also simple; however, their validity and accuracy have been questioned. In this study, the flow characteristics of jellyfish valves are evaluated and analyzed for steady and pulsatile flow conditions. The analysis is given in terms of velocity and shear stress distributions for a cardiac flow rate of 4.5l/min, and the corresponding steady flow rate is measured at two locations, 0.5D and 1D downstream of the valve face (D being the diameter of the pipe). At the 0.5D location, the velocity profile results obtained for both flow conditions indicated that jetting flow occurred close to the wall, and flow reversal as well as stagnation zones occurred in the core of the valve chamber. These phenomena were also evident in the shear stress profiles for both pulsatile and steady flow conditions. At this location, the maximum difference between the steady and pulsatile values of peak velocity is about 18%. However, the maximum difference between the peak shear stresses was in the range of 5%–7%. At the 1D location, the flow characteristics observed under both the pulsatile and steady flow conditions were almost identical, with a maximum difference between the peak values of less than 4%. From the data presented here, it can be stated that, at least in the initial optimization of the valve hemodynamic performance, the steady hydrodynamic evaluation of the valve could be an effective tool for analyzing the flow characteristics.     

Correlation between ventricular flow field and valve closing sound of mechanical mitral prostheses

The Jyros (JR) valve and the newer On-X and MIRA valves, all installed antianatomically, were compared with the St. Jude Medical (SJM) valve in the mitral position to study the effects of valve design differences on the down-stream flow field and the associated valve closing sound. The dynamic particle image velocimetry method utilizing a high-speed video flow visualization technique was used to map the velocity field, and wavelet analysis of the sound was used to find the correlation between the ventricular flow field and the valve closing sound. Based on the experimental data, the following general conclusions can be made. In the velocity field directly below the mitral valve, where the distinct characteristic differences of the valve designs will be evident, twin symmetrical circulations were observed due to the divergent nature of the flow generated by the two inclined half-disks with the valve installed in the anti-anatomical orientation; the SJM, the On-X, and the MIRA valves generated a centrally downward circulation that opposed the valve leaflet closing movement, and resulted in relatively loud valve closing sounds.     

A SAM valve prosthesis in the mitral position: report of a case of long-term survival

No long-term survivals over 20 years after valve replacement with SAM (Sakakibara-Arai-Mera) valve prostheses have been described. We report a 57-year-old woman who survived for 31 years after mitral valve replacement with the SAM valve (Type M, 5M). Echocardiography revealed remarkable dilatation of the left atrium and moderate tricuspid regurgitation. Cineradiography, however, showed no restricted or asymmetric disc movement of the SAM valve. Cardiac catheterization revealed moderate pulmonary hypertension (64/30mmHg), with a mean pulmonary capillary wedge pressure of 25mmHg and a mean transprosthetic pressure gradient of 13mmHg. The mitral valve area was calculated to be 0.9 cm². No findings of pannus overgrowth around the SAM valve were confirmed on echocardiograms or left ventriculograms. Although the diagnosis of prosthetic valve obstruction resulting from pannus formation was suspected, the patient strongly refused replacement of the SAM valve because of her poor prognosis with bilateral breast cancer with systemic metastases. We believe that this patient may be the last living patient with the SAM valve.     

Effect of the flow field of mechanical bileaflet mitral prostheses on valve closing

Antianatomically installed Jyros (JR) and ATS valves were compared with the St. Jude Medical (SJM) valve in the mitral position to study the effects of valve design on the downstream flow field and associated closing sounds using a particle image velocimetry (PIV) method utilizing a high-speed video flow visualization technique to map the velocity field and sound measurement to confirm claims by the manufacturer. Based on the experimental data, the following general conclusions can be made: in the velocity field directly below the mitral valve, where distinct characteristic differences in valve design can be seen, symmetrical twin circulations were observed because of the divergent nature of the flow generated by the two inclined half-disks installed in the antianatomical orientation; the SJM valve, which produced central downward circulation, is contrasted to the two other valves, which produced peripheral downward circulation. These differences may play an important role in the closing behavior of the valve leaflets, thus affecting the generation of the valve closing sound.     

The CarboMedics prosthetic heart valve: experience with 180 implants

At Jichi Medical School Hospital, three types of mechanical prosthetic valves (CarboMedics, Omnicarbon, Bicarbon) were used without randomization from 1991 to 2000. A retrospective study of valve replacements done between June 1991 and November 2000 utilizing 180 CarboMedics valves in 145 patients who had not previously undergone prosthetic valve replacement or aortic root and/or arch replacement was conducted to evaluate midterm patient outcomes to assess the future continuous use of CarboMedics valves. Women made up 47.6% of the patients and the mean age was 57.5 years (range 12–80 years). Preoperative New York Heart Association functional class was III or IV in 92.4% (134/145) of patients. Mean follow-up of 4.5 years (range 0–10.0 years) was 95.9% complete, with a total of 628 patient-years (PY). Early (within 30 postoperative days) mortality was 5.5% (8 of 145): 3 from hemorrhage, 3 from nonvalve-related heart failure, 1 from infection, and 1 from arrhythmia. There were 16 late deaths (2.54%/PY): 1 from hemorrhage, 4 from unknown causes/sudden death, 4 from nonvalve-related heart failure, and 7 from other noncardiac causes. A total of 121 patients (83.0%) were alive at the last follow-up, done in November 2000. The linearized death rate was 3.82%/year (including 1.11%/year for valve-related deaths). Linearized death rates from various causes were: bleeding, 0.96%/year; thromboembolism, 1.11%/year; thrombosis, 0.39%/year; perivalvular leak, 0.96%/year; endocarditis, 0%/year; hemolysis, 0%/year; and reoperation, 0.63%/year. No structural valve failure was observed. Comparative early mortality rates of valve replacement without aortic root replacement or arch replacement, excluding repeat valve replacement operations, in our institute, were 3.5% (12/307) for all valve types used contemporaneously, 2.6% (2/76) for Omnicarbon valves, and 2.3% (2/86) for Bicarbon valves. Although the CarboMedics valve had a rather high mortality rate of 5.5% (8/145) compared with the total early mortality rate of 3.5%, the low incidence of valve-related complications might support the continued use of the CarboMedics valve for valve replacement.     

心脏瓣膜置换后早期住院患者死亡因素分析

背景：积极加强对高危患者心脏瓣膜置换前、中和置换后的处理,可降低心脏瓣膜置换后早期死亡率。 目的：分析心脏瓣膜病患者置换治疗后早期住院死亡的危险因素,提高手术治愈率。 方法：回顾分析488例心脏瓣膜病患者行手术治疗作为临床资料;以置换后早期住院死亡为研究终点,采用单因素及多因素Logistic回归方法分析置换后早期死亡的危险因素。 结果与结论：488例心脏瓣膜置换患者中,置换后早期死亡27例,总死亡率5.5%。主要的死亡原因是低心排综合征、恶性心律失常、多器官功能衰竭。单因素分析显示：年龄≥60岁、心功能IV级、联合瓣膜手术以及同期冠状动脉旁路移植、左室射血分数≤50%、左室舒张末内径≥70 mm、体外循环时间≥120 min、主动脉阻断时间≥ 60 min与心脏瓣膜后死亡的发生具有相关性(P < 0.05)。多因素Logistic回归分析结果：年龄≥ 60岁、心功能IV级、瓣膜手术同期冠状动脉旁路移植、体外循环时间≥120 min、左室射血分数≤50% 、左室舒张末内径≥70 mm是影响心瓣膜置换后早期死亡的独立危险因素。重视围手术期处理,针对这些因素合理把握手术指征、选择合适的手术方式以及心肌保护,可以进一步降低这类患者手术并发症和病死率。 中国组织工程研究杂志出版内容重点：肾移植;肝移植;移植;心脏移植;组织移植;皮肤移植;皮瓣移植;血管移植;器官移植;组织工程全文链接：     

Effect of the mechanical prosthetic mono- and bileaflet heart valve orientation on the flow field inside the simulated ventricle

Two groups of typical contemporary mechanical heart valves, the Advancing the Standard (ATS) and the Carbomedics (CM) valve (of bileaflet design) and the Bjork-Shiley (BS) mono and Bicer-Val (BV) valves (of tilting-disc design), were tested in the mitral position under the pulsatile-flow condition. This study extends a previous report studying the effect of orientation of the St. Jude Medical (SJM) valve, representing bilcaflet valve design, and the Meditronic-Hall (MH) valve, representing mono-leaflet valve design. The test program utilized a flow visualization technique to map the velocity field inside the simulated ventricle. The study was carried out using a sophisticated cardiac simulator in conjunction with a high-speed video system (200 frames·s⁻¹). The continuous monitoring of velocity-vector time histories revealed useful details about the complex flow and helped establish the locations and times of the peak parameter values. Comparison of the velocity profiles at corresponding flow phases reveals the effects of the differences in valve design and orientation. Based on precise examination of the data, the following general conclusions can be made: pulsatile flow creates three distinct flow phases consisting of accelerating, peak, and decelerating flow; the bileaflet CM and ATS valves in the antianatomical orientation generally create a single, large circulatory flow; the ATS valve scems to offer smoother flow patterns, similar to the SJM valve; and the monoleaflet BV valve and the BS monostrut valve seem to affect the flow characteristics more dramatically, with the posterior orientation exhibiting simple and stable circulatory flow.     

Role of computational fluid mechanics in the analysis of prosthetic heart valve flow

The paper aims to present the strengths and weaknesses of computational fluid mechanics (CFM) compared with existing in vitro haemodynamic techniques such as LDA, hot-wire anemometry and static pressure measurement, and to discuss the application of CFM to the analysis of prosthetic heart valve flow. It presents a brief summary of existing methods used in analysing in vitro heart valve flow (along with CFM), the special problems inherent in each method and the quantities each is capable of giving. The analysis then goes on to present examples of information yielded by CFM. It also contains a brief discussion of the data requirements for the analysis of heart valve performance and the clinical relevance of fluid dynamic occurrences. The conclusion drawn is that CFM has a major role to play in the analysis of prosthetic heart valve flow and design because of the improved availability of data afforded and the increased correlation between CFM and clinical flow regimes, due to the ability to consider realistic models of blood.     

Method of ranking of heart valve characteristics at mitral position based on statistical model analysis

The purpose of this study was to explore a valve selection criterion based on the impact force generated at valve closure, and to test a statistical mathematical model for comparing valve performance. The impact force generated at valve closure in the mitral position was measured continuously, using a load cell mounted in the left atrial section of a mock circulatory system. Eight clinical valves were tested. The data obtained from the in vitro test were subjected to multiregression analysis, to enable systematic comparison of the impact forces of these valves. Further-more, class I quantification, theory was applied to construct the statistical mathematical model. As a result, the following interaction effect was observed in the statistical model. (1) The impact force generated at valve closure had a lower value in valves of smaller diameter. (2) The ranking of 29-mm-diameter valves by impact force was different for the flow region. Under the physiological flow condition of 4–61/min, high impact forces were generated in all valves, in the order Björk-Shiley monostrut, ATS, St. Jude medical, CarboMedics. We consider that low impact force at valve closure is desirable, upon consideration of the influence on the annulus tissue at valve replacement. From these findings, the results of the multiregression analysis provide indications for choosing the optimal value for patients with severe mitral insufficiency (MI).     

Computer graphics analysis of stresses in blood flow through a prosthetic heart valve

Fluid dynamics principles and numerical analysis techniques are applied to the study of stress distribution in blood caused by the motion of the occluder in a prosthetic heart valve. An interactive computer graphics program is developed for the simulation of the flow process and the pictoral presentation of the solution for analysis. Resulting graphics displays show the stress distribution and other flow parameters which describe the movement of a disc occluder from fullclosed position to an almost full-open position. The possible contributions of this study to the understanding of hemolysis and thrombosis associated with prosthetic heart valves are discussed.     

Effect of mechanical prosthetic heart valve orientation on the flow field inside the simulated ventricle: Comparison between St. Jude Medical Valve and Medtronic-Hall Valve

Two typical contemporary mechanical heart valves, with different designs (St. Jude Medical and Medtronic-Hall), were tested in the mitral position under pulsatile flow conditions. The test program used the flow visualization technique to map the velocity field inside the simulated ventricle. The study was carried out using a sophisticated cardiac simulator in conjunction with a highspeed video system (200 frames/s). The continuous monitoring of velocity vector time histories revealed useful details about the complex flow and helped establish the location and time of the peak parameter values. We conclude that (1) the SJM valve with antianatomical position creates a large single circulatory flow; and (2)the configuration of the MH valve seems to affect the flow characteristics more dramatically, and the posterior orientation exhibits a simple and stable circulatory flow.     

Flow analysis of the bileaflet mechanical prosthetic heart valves using laser Doppler anemometer: Effect of the valve designs and installed orientations to the flow inside the simulated left ventricle

Ever since the first introduction of the ball-type valve by Hufnagel in 1952, which was installed in the descending aorta to correct aortic valve insufficiency, great efforts have been aimed to produce a hemodynamically and structurally superior prosthetic heart valve. Bileaflet valves, commercially initiated by the St. Jude medical (SJM) valve, perform satisfactorily, and now the majority of the mechanical-type prosthetic heart valves used clinically are of this type. The recent trend in bileaflet valve design seems to be concentrated on the hinge mechanism and leaflet design to improve performance against thromboembolic complications and hemolysis. This paper studied the effects of hinge location, leaflet configuration, valve opening angle, and valve installed orientation to the flow field inside the simulated ventricle using laser Doppler anemometry. As a model prosthetic valve, the SJM valve was selected as a reference, and newer bileaflet valves, including the ATS, the Carbomedics (CM), and the Jyros (JR) valves, were selected for comparison. The test program also utilized a flow visualization technique to map the velocity field inside the simulated ventricle to complement the information obtained using the LDA system. Comparison of the velocity profiles at corresponding flow phases revealed the effects of the differences in valve design and orientation. Based on precise examination of the data, the following general conclusions can be made: all valves (SJM, ATS, CM, and JR) show distinct circulatory flow patterns when the valve is installed in the antianatomical orientation. The small differences in hinge location and leaflet configuration can generate noticeable differences, particularly during the accelerating flow phase of the valve. The ATS and the CM valves open less during the forward flow phase, and this results in generally diverse and less distinct flow patterns and slower velocity. This is particularly noticeable for the flow through the central orifice. The SJM valve maintains a relatively higher velocity through the central orifice. The curved leaflet JR valve generates higher but divergent flow during the accelerating and peak flow phases.     

Physical principles of the Edinburgh prosthetic heart valve

A new type of prosthetic heart valve, at present under development, has been designed according to a set of general assumptions, here made explicit, concerning the interaction of flowing blood with artificial structures. On these assumptions, it is shown that the characteristics desirable in a prosthetic heart valve are supplied by a form of butterfly valve in which an occluder, capable of rotation about a nearly diametral axis in a smooth-bore housing, rapidly assumes a low-drag position aligned with the forward flow and closes rapidly on flow reversal. These desiderata, not furnished by conventional butterfly valves, are achieved in the Edinburgh design, in which an occluder of suitable aerofoil shape is mounted pivotally in a housing of conical or similarly divergent bore. Certain forms of carbon are suitable materials of construction. Preliminary data forin vivo (canine) performance are given for Edinburgh valves fabricated from graphite coated with pyrolytic carbon.     

Mathematical mdoel for turbulent blood flow through a disk-type prosthetic heart valve

Computational fluid dynamic techniques are used to construct a mathematical model for turbulent blood flow through a disk-type prosthetic heart valve in the aortic position. The TEACH computer code is used to solve the k-6 turbulence model numerically over the axisymmetric flow field of the valve during systole. Stream function, mean axial velocity profiles, turbulent shear stresses and wall shear stress distributions are computed for Reynolds numbers between Re_D=600 and 10 000 (corresponding to steady flow rates of 2·63 lmin⁻¹ and 43·89lmin⁻¹, respectively). The location, length and maximum reverse flow velocities of separated, flow regions are presented and compared with experimental observations. The largest computed mean axial velocities are 4·4 to 4·8 times the inflow velocity and occur near the downstream corner of the sewing ring. The maximum wall shear stress computed is 229·7 Nm⁻² at the upstream corner of the disk occluder for Re_D=10000. The location of maximum walls shear stress occurs at the downstream corner of the sewing ring for Re_D≤2000. Turbulent shear stresses of up to 380·7 Nm⁻² are computed in the region between the sewing ring and the disk occluder for the physiological Reynolds number Re_D=6054. The numerical solutions are shown to compare favourably with available experimental measurements.     

Infective endocarditis in patients who have undergone transcatheter aortic valve implantation: a review

BackgroundTranscatheter aortic valve implantation (TAVI) has been approved for the treatment of severe aortic stenosis since 2008 and recent trials have shown that TAVI is at least non-inferior to surgical aortic valve replacement (SAVR) with regards to short-term efficacy and safety in patients across all surgical risk profiles. Prosthetic valve endocarditis of the transcatheter heart valve is a feared complication; data on the risk of infective endocarditis (IE) subsequent to TAVI are now gradually emerging.ObjectivesWe set forth to conduct a review of the incidence, diagnosis, microbial aetiologies, prevention, outcome and management of TAVI-IE.SourcesFrom the MEDLINE database we included a total of 12 observational studies and five studies of long-term results from randomized controlled trials.ContentThe incidence of TAVI-IE was reported to be between 0.7% and 3.0% per person-year. The most common microbes were reported to be enterococci, Staphylococcus aureus, streptococci and coagulase-negative staphylococci. International guidelines on prevention strategies of IE recommend good sanitary conditions including cutaneous care, good oral hygiene and good care of dialysis catheters. Antibiotic prophylaxis is recommended by guidelines prior to dental procedures in patients with TAVI; however, evidence is sparse. The majority of the patients included in this review with TAVI-IE had an indication for surgical intervention due to IE (50.0% or more); however, only a small subset of the patients underwent surgery (16.4% or less). The in-hospital mortality was around 25%, i.e. of the same order of magnitude as in prosthetic valve IE in general, but varied substantially between studies (from 11% to 64%).ImplicationsThe US Food and Drug Administration's approval of TAVI in patients at low surgical risk may change the characteristics of patients with TAVI, which may influence the incidence, management, and outcome of patients with TAVI-IE.     

Tri-layered elastomeric scaffolds for engineering heart valve leaflets

Tissue engineered heart valves (TEHVs) that can grow and remodel have the potential to serve as permanent replacements of the current non-viable prosthetic valves particularly for pediatric patients. A major challenge in designing functional TEHVs is to mimic both structural and anisotropic mechanical characteristics of the native valve leaflets. To establish a more biomimetic model of TEHV, we fabricated tri-layered scaffolds by combining electrospinning and microfabrication techniques. These constructs were fabricated by assembling microfabricated poly(glycerol sebacate) (PGS) and fibrous PGS/poly(caprolactone) (PCL) electrospun sheets to develop elastic scaffolds with tunable anisotropic mechanical properties similar to the mechanical characteristics of the native heart valves. The engineered scaffolds supported the growth of valvular interstitial cells (VICs) and mesenchymal stem cells (MSCs) within the 3D structure and promoted the deposition of heart valve extracellular matrix (ECM). MSCs were also organized and aligned along the anisotropic axes of the engineered tri-layered scaffolds. In addition, the fabricated constructs opened and closed properly in an ex vivo model of porcine heart valve leaflet tissue replacement. The engineered tri-layered scaffolds have the potential for successful translation towards TEHV replacements.     

The surface anatomy of the human aortic valve as revealed by scanning electron microscopy

Summary The anatomy of the human aortic valve was studied by SEM in 36 subjects without cardiac pathology who had died of various accidental causes. Villous and lamellar tissue excrescences were observed at the node of Arantius and at the limit between the lunules and the load-bearing portion of the leaflets. The morphology of these structures suggests that they represent areas in which valve tissue becomes detached into the bloodstream. Fenestrations were present in the lunules of 14 specimens, with a higher incidence in specimens from subjects who were middle-aged or older. Our observations suggest that fenestrations appear initially as small perforations which then coalesce to form larger apertures.Two main types of endothelial cells, elongated and polygonal were detected on the endothelial surface of the leaflets. Both types of cells display a constant mode of arrangement on the different segments of the leaflets (lunules, node of Arantius and load-bearing portion of the leaflet). The possible relationships between endothelial cell morphology and the pattern of mechanical stress to which the leaflets are subjected is discussed.     

Preparation of gradient biomaterial used for artificial mechanical heart valve

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