Advances in prosthetic heart valves: fluid mechanics of aortic valve designs

The in vitro hemodynamic characteristics of a variety of mechanical and tissue heart valve designs used during the past two decades were investigated in the aortic position under pulsatile flow conditions. The following valve designs were studied: Starr-Edwards ball and cage (model 1260), Bj?rk-Shiley tilting disc (convexo-concave model), Medtronic-Hall tilting disc, St. Jude Medical bileaflet, Carpentier-Edwards porcine and pericardial (models 2625, 2650 and 2900), Hancock porcine (models 250 and 410) and Ionescu-Shiley standard pericardial. The Starr-Edward ball and cage, Bj?rk-Shiley tilting disc, Carpentier-Edwards porcine (model 2625) and Ionescu-Shiley standard pericardial valves were designed prior to 1975, while the Medtronic-Hall tilting disc, St. Jude Medical bileaflet, Hancock porcine (model 250), Hancock II porcine (model 410), Carpentier-Edwards porcine (model 2650) and Carpentier-Edwards pericardial (model 2900) valves were designed after 1975. The pressure drop results indicated that the valves designed prior to 1975 had performance indices of 0.30 to 0.45, whereas the valves designed after 1975 had performance indices of 0.40 to 0.70. The regurgitant volumes were higher for the mechanical designs (5.0 to 11.0 cm3/beat) compared to the tissue bioprostheses (1.0 to 5.0 cm3/beat). Two-dimensional laser Doppler anemometry studies indicated that the valves designed after 1975 tended to create more centralized flow fields, with reduced levels of turbulent shear stresses. However, none of the current valve designs is ideal: they all create areas of stasis and/or regions of low velocity reverse flow; and regions of elevated turbulent shear stresses that are capable of causing sub-lethal and/or lethal damage to the formed elements of blood.     

Noninvasive detection of mechanical prosthetic heart valve disorder

Auscultation is a widely used efficient technique by cardiologists for detecting the heart conditions. Since the mechanical prosthetic heart valves are widely used today, it is important to develop a simple and efficient method to detect abnormal mechanical valves. In this paper, the mechanical prosthetic heart valve sounds are analyzed by using different power spectral density (PSD) estimation techniques. To improve the classification accuracy of heart sounds, we propose two different feature extraction schemes, i.e., a modified local discriminant bases (LDB) scheme and a Hilbert-Huang Transform (HHT)-based scheme. A database of 150 heart sounds is used in this study and an average classification accuracy of 97.3% is achieved for both the two feature extraction schemes, when a generic linear discriminant analysis (LDA) classifier is used in the classification stage.     

Paecilomyces javanicus endocarditis of native and prosthetic aortic valve

A 41-year-old diabetic woman developed endocarditis of the aortic valve caused by Paecilomyces javanicus six years after insertion of a porcine mitral valve heterograft. The patient died shortly after aortic valve replacement. Autopsy revealed vegetations of the aortic heterograft, valve ring abscess and ascending aortitis due to Paecilomyces. There was no involvement of the mitral valve heterograft. Lesions due to mycotic emboli were found in the kidneys, spleen, and brain. Cultures of the surgically removed aortic valve and of the kidney at autopsy produced rapid growth of P. javanicus. The gross and microscopic pathologic and cultural characteristics of this organism are described with a review of the literature. Previously reported cases of Paecilomyces endocarditis occurred only in prosthetic heart valves. This is the first known report of P. javanicus endocarditis of a native valve and its prosthetic heart valve heterograft.     

Including aortic valve morphology in computational fluid dynamics simulations: Initial findings and application to aortic coarctation

Computational fluid dynamics (CFD) simulations quantifying thoracic aortic flow patterns have not included disturbances from the aortic valve (AoV). 80% of patients with aortic coarctation (CoA) have a bicuspid aortic valve (BAV) which may cause adverse flow patterns contributing to morbidity. Our objectives were to develop a method to account for the AoV in CFD simulations, and quantify its impact on local hemodynamics. The method developed facilitates segmentation of the AoV, spatiotemporal interpolation of segments, and anatomic positioning of segments at the CFD model inlet. The AoV was included in CFD model examples of a normal (tricuspid AoV) and a post-surgical CoA patient (BAV). Velocity, turbulent kinetic energy (TKE), time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) results were compared to equivalent simulations using a plug inlet profile. The plug inlet greatly underestimated TKE for both examples. TAWSS differences extended throughout the thoracic aorta for the CoA BAV, but were limited to the arch for the normal example. OSI differences existed mainly in the ascending aorta for both cases. The impact of AoV can now be included with CFD simulations to identify regions of deleterious hemodynamics thereby advancing simulations of the thoracic aorta one step closer to reality.     

Case report of Streptomyces endocarditis of a prosthetic aortic valve.

We describe the first case of prosthetic valve endocarditis due to a Streptomyces sp. The patient presented with fever, cutaneous embolic lesions, and bacteremia 3 months after aortic valve replacement. Treatment required valve replacement and a long course of parenteral imipenem.     

Propionibacterium acnes as a cause of prosthetic valve aortic root abscess

Propionibacterium acnes isolates usually have relatively low virulence and are often classified as contaminants when isolated from blood and tissue cultures. We report a patient with Propionibacterium acnes bacteremia and late prosthetic valve endocarditis, complicated by an aortic root abscess.     

Experimental analysis of fluid mechanical energy losses in aortic valve stenosis: Importance of pressure recovery

Current methods for assessing the severity of aortic stenosis depend primarily on measures of maximum systolic pressure drop at the aortic valve orifice and related calculations such as valve area. It is becoming increasingly obvious, however, that the impact of the obstruction on the left ventricle is equally important in assessing its severity and could potentially be influenced by geometric factors of the valve, causing variable degrees of downstream pressure recovery. The goal of this study was to develop a method for measuring fluid mechanical energy losses in aortic stenosis that could then be directly related to the hemodynamic load placed on the left ventricle. A control volume form of conservation of energy was theoretically analyzed and modified for application to aortic valve stenosis measurements.In vitro physiological pulsatile flow experiments were conducted with different types of aortic stenosis models, including a venturi meter, a nozzle, and 21-mm Medtronic-Hall tilting disc and St. Jude bileaflet mechanical valves. The energy loss created by each model was measured for a wide range of experimental conditions, simulating physiological variation. In all cases, there was more energy lost for the nozzle (mean=0.27 J) than for any other model for a given stroke volume. The two prosthetic valves generated approximately the same energy losses (mean=0.18 J), which were not statistically different, whereas the venturi meter had the lowest energy loss for all conditions (mean=0.037 J). Energy loss correlated poorly with orifice pressure drop (r ²=0.34) but correlated well with recovered pressure drop (r ²=0.94). However, when the valves were considered separately, orifice and recovered pressure drop were both strongly correlated with energy loss (r ²=0.99, 0.96). The results show that recovered pressure drop, not orfice pressure drop, is directly related to the energy loss that determines pump work and therefore is a more accurate measure of the hemodynamic significance of aortic stenosis.     

A patient diagnosed with pauciarticular juvenile rheumatoid arthritis after a mechanical prosthetic valve replacement due to aortic regurgitation.

Valvular heart disease is a rare complication of juvenile rheumatoid arthritis (JRA), with most cases associated with polyarticular JRA. The aortic valve is most commonly affected, and valvular involvement occurs months or years after the onset of JRA. Reported cases of valvular heart disease in patients with JRA in a pauciarticular pattern are rare. We report a case of severe aortic insufficiency in a 12-year-old boy who underwent aortic valve replacement before diagnosis of JRA with a pauciarticular pattern.     

Measurements of steady flow through a bileaflet mechanical heart valve using stereoscopic PIV

Computational modeling of bileaflet mechanical heart valve (BiMHV) flow requires experimentally validated datasets and improved knowledge of BiMHV fluid mechanics. In this study, flow was studied downstream of a model BiMHV in an axisymmetric aortic sinus using stereoscopic particle image velocimetry. The inlet flow was steady and the Reynolds number based on the aortic diameter was 7600. Results showed the out-of-plane velocity was of similar magnitude as the transverse velocity. Although additional studies are needed for confirmation, analysis of the out-of-plane velocity showed the possible presence of a four-cell streamwise vortex structure in the mean velocity field. Spatial data for all six Reynolds stress components were obtained. Reynolds normal stress profiles revealed similarities between the central jet and free jets. These findings are important to BiMHV flow modeling, though clinical relevance is limited due to the idealized conditions chosen. To this end, the dataset is publicly available for CFD validation purposes.     

Numerical comparison of the closing dynamics of a new trileaflet and a bileaflet mechanical aortic heart valve

The closing velocity of the leaflets of mechanical heart valves is excessively rapid and can cause the cavitation phenomenon. Cavitation bubbles collapse and produce high pressure which then damages red blood cells and platelets. The closure mechanism of the trileaflet valve uses the vortices in the aortic sinus to help close the leaflets, which differs from that of the monoleaflet or bileaflet mechanical heart valves which mainly depends on the reverse flow. We used the commercial software program Fluent to run numerical simulations of the St. Jude Medical bileaflet valve and a new trileaflet mechanical heart valve. The results of these numerical simulations were validated with flow field experiments. The closing velocity of the trileaflet valve was clearly slower than that of the St. Jude Medical bileaflet valve, which would effectively reduce the occurrence of cavitation. The findings of this study are expected to advance the development of the trileaflet valve.     

The closing behavior of mechanical aortic heart valve prostheses

Mechanical artificial heart valves rely on reverse flow to close their leaflets. This mechanism creates regurgitation and water hammer effects that may form cavitations, damage blood cells, and cause thromboembolism. This study analyzes closing mechanisms of monoleaflet (Medtronic Hall 27), bileaflet (Carbo-Medics 27; St. Jude Medical 27; Duromedics 29), and trileaflet valves in a circulatory mock loop, including an aortic root with three sinuses. Downstream flow field velocity was measured via digital particle image velocimetry (DPIV). A high speed camera (PIVCAM 10-30 CCD video camera) tracked leaflet movement at 1000 frames/s. All valves open in 40-50 msec, but monoleaflet and bileaflet valves close in much less time (< 35 msec) than the trileaflet valve (>75 msec). During acceleration phase of systole, the monoleaflet forms a major and minor flow, the bileaflet has three jet flows, and the trileaflet produces a single central flow like physiologic valves. In deceleration phase, the aortic sinus vortices hinder monoleaflet and bileaflet valve closure until reverse flows and high negative transvalvular pressure push the leaflets rapidly for a hard closure. Conversely, the vortices help close the trileaflet valve more softly, probably causing less damage, lessening back flow, and providing a washing effect that may prevent thrombosis formation.     

A novel technique for high resolution analysis of the cytoskeleton

A new technique is described for producing and examining carbon-platinum replicas of the cytoskeleton of cultured cells. This technique allows the individual components of the cytoskeleton to be visualized and positively identified in the transmission electron microscope, and also permits an analysis of the 3-dimensional disposition of these components.     

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.     

Validation of a numerical 3-D fluid–structure interaction model for a prosthetic valve based on experimental PIV measurements

A numerical 3-D fluid–structure interaction (FSI) model of a prosthetic aortic valve was developed, based on a commercial computational fluid dynamics (CFD) software program using an Arbitrary Eulerian Lagrangian (ALE) formulation. To make sure of the validity of this numerical model, an equivalent experimental model accounting for both the geometrical features and the hydrodynamic conditions was also developed. The leaflet and the flow behaviours around the bileaflet valve were investigated numerically and experimentally by performing particle image velocimetry (PIV) measurements. Through quantitative and qualitative comparisons, it was shown that the leaflet behaviour and the velocity fields were similar in both models. The present study allows the validation of a fully coupled 3-D FSI numerical model. The promising numerical tool could be therefore used to investigate clinical issues involving the aortic valve.     

经心尖主动脉瓣置换术治疗高危单纯无钙化主动脉瓣关闭不全的手术配合

目的探讨国产J-Valve?支架瓣膜行经心尖主动脉瓣置换(TAVR)术治疗高危单纯无钙化主动脉瓣关闭不全的手术配合方法。 方法收集2017年3月至2018年3月在首都医科大学附属北京安贞医院高危单纯无钙化主动脉瓣关闭不全患者资料,共15例。所有患者均使用国产J-Valve?系统为患者行TAVR术。经过细致的术前评估(包括术前访视、熟悉仪器设备、介入耗材设备等)、术中流畅的手术配合[包括严格遵循无菌原则、术中患者体温保护、X线防护、激活全血凝固时间(ACT)的监测以及支架瓣膜的装配等]和术中安全管理(包括防止输送器移位和动脉置管的护理等)。观测患者术中是否使用心肺转流、发生心室快速起搏、中转行常规体外循环下TAVR术,是否有冠状动脉阻塞、植入瓣膜是否有移位,有无瓣膜内狭窄及瓣周漏等情况发生,观测术后即刻平均主动脉瓣跨瓣压差;患者在ICU是否顺利脱离呼吸机拔除气管插管,术中平均出血量、患者在ICU时间和呼吸机辅助通气时间、射血分数以及是否存在瓣周漏等;了解患者心功能分级、活动耐量以及是否存在胸闷、心绞痛等症状。 结果本研究中所有患者均成功完成TAVR术,未使用心肺转流、未发生心室快速起搏,无中转行常规体外循环下TAVR术,未发生冠状动脉阻塞或植入瓣膜移位,未见瓣膜内狭窄及瓣周漏等情况。术后即刻平均主动脉跨瓣压差为[5.8(4.9,12.9)] mmHg(1 mmHg＝0.133 kPa)。所有患者在ICU均顺利脱离呼吸机拔除气管插管,术中平均出血量为[200.0 (100.0, 500.0)]mL,患者在ICU时间为(1.2±0.4) d,呼吸机辅助通气时间为[19.0 (8.5, 23.5)] h,平均射血分数为(56.2±15.6)%,仅有2例患者存在微量瓣周漏。末次随访中,10例患者心功能Ⅰ级,4例为Ⅱ级,1例为Ⅲ级;患者的活动耐量都较术前明显改善;患者术后胸闷、心绞痛等症状较术前明显改善。 结论手术室护士正确掌握TAVR术的手术配合方法,术前做好患者的心理护理以及各项术前准备,手术过程中与外科医师密切配合,是患者手术成功的保证。     

Effects of prosthetic valve placement on mitral annular dynamics and the left ventricular base

Insertion of a rigid mitral prosthesis impairs the function of the mitral annulus and induces systolic narrowing of the left ventricular outflow tract (LVOT). To study this mechanism, we investigated dynamic changes in the left ventricular (LV) base, which consists of the mitral annulus and LVOT orifice. In seven patients with mechanical mitral valve prostheses and eight normal subjects, the image of the LV base was reconstructed three-dimensionally and its dynamic change during systole was studied. In the patients, the rigid prosthetic valve (=mitral annulus) tilted toward the left ventricle with a hinge point at the posterior mitral annulus during systole. The left ventricular base exhibited contraction, but the size of the prosthetic valve was constant. As a consequence, the prosthetic valve occupied more of the left ventricular base, which resulted in narrowing of the LVOT. In the normal subjects, the mitral annulus did not interfere with the region of the LVOT orifice during systole as the mitral annulus underwent both dorsiflexion and contraction. Thus, fixation of the mitral annulus induces an anti-physiologic motion of the annulus. Conscious preservation of annular flexibility in mitral valve surgery is important in avoiding potential dynamic LVOT obstruction.     

Time-dependent mechanical properties of aortic valve cusps: Effect of glycosaminoglycan depletion

Aortic valve (AV) performance is closely linked to its structural components. Glycosaminoglycans (GAGs) are thought to influence the time-dependent properties of living tissues. This study investigates the effect of GAGs on the viscoelastic behaviour of the AV. Fresh porcine AV cusps were either treated enzymatically to remove GAGs or left untreated (control). The specimens were tested for stress relaxation and tensile properties under equibiaxial load conditions. The stress relaxation curves were fitted using a double exponential decay equation and the early relaxation constant (τ₁) and late relaxation constant (τ₂) calculated for each specimen. Immunohistochemistry confirmed the successful depletion of both sulphated and non-sulphated GAGs from the AV cusps. A statistical increase in τ₁ was found for both the radial and circumferential directions between the control and –GAGs group (radial, control 17.37 s vs. –GAGs 25.65 s; circumferential, control 21.47 s vs. –GAGs 27.37 s). It was also found that τ₁ differed between the two directions for the control group but not after GAG depletion (control, radial 17.37 s vs. circumferential 21.47 s; –GAGs, radial 25.65 s vs. circumferential 27.37 s). No effect on stiffness was found. The results showed that the presence of GAGs influences the mechanical viscoelastic properties of the AV but has no effect on the stiffness. The natural anisotropy, which reflects the relaxation kinematics, is lost after GAG depletion.     

Cure of bartonella endocarditis of a prosthetic aortic valve without surgery: value of serologic follow-up

Bartonella species are emerging as an important cause of blood culture-negative endocarditis, but the optimal management of this disease has not been fully defined. We describe a case of subacute Bartonella henselae endocarditis of a prosthetic aortic valve in an immunocompetent woman that was cured with long-term antibiotic therapy alone. In addition, we demonstrate that follow-up of serologic titers against B. henselae was helpful in assessing definitive cure of the infection.