Small Scale Flow Structure Evolution During Mechanical Heart Valve Closure

2013 ◽  
Author(s):  
J. Mousel ◽  
H. S. Udaykumar ◽  
K. B. Chandran
Keyword(s):  
Heart Valves ◽  
Thrombus Formation ◽  
Mechanical Heart Valve ◽  
Structure Evolution ◽  
Small Scale ◽  
Leakage Flows ◽  
Large Pressure ◽  
Large Pressure Gradient ◽  
Valve Position ◽  
Systolic Phase

Despite half a century of use, mechanical heart valves still require further research to reduce the non-physiologic nature of the flow field, which is the source of potential medical complications, of which the most serious complication is thrombus formation [1]. In the systolic phase of the flow, excessive fluid stresses are generated by the non-physiologic flow patterns [2, 3]. In the closed valve position, a large pressure gradient is imposed across the device which leads to the generation of strong and damaging small-scale leakage flows that entrain platelets such that they are exposed to elevated stresses for excessive time durations [4–6].

Design Optimization of a Mechanical Heart Valve for Reducing Valve Thrombogenicity: A Case Study With ATS Valve

2010 ◽  
Author(s):  
Gaurav Girdhar ◽  
Yared Alemu ◽  
Michalis Xenos ◽  
Jawaad Sheriff ◽  
Jolyon Jesty ◽  
...  
Keyword(s):  
Heart Valves ◽  
Thrombus Formation ◽  
Anticoagulation Therapy ◽  
Mechanical Heart Valve ◽  
Ventricular Assist Devices ◽  
Circulatory Support ◽  
Ventricular Assist ◽  
Mechanical Circulatory Support Devices ◽  
Artificial Hearts

Flow past mechanical heart valves (MHV) in mechanical circulatory support devices including total artificial hearts and ventricular assist devices, is primarily implicated in thromboembolism due to non-physiological flow conditions where the elevated stresses and exposure times are sufficiently high to cause platelet activation and thrombus formation. Mitigation of this risk requires lifelong anticoagulation therapy and less thrombogenic MHV designs should therefore be developed by device manufacturers [1].

Argatroban and bivalirudin compared to unfractionated heparin in preventing thrombus formation on mechanical heart valves

2009 ◽  
Vol 101 (06) ◽  
pp. 1163-1169 ◽  
Author(s):  
Torsten Linde ◽  
Thomas Michel ◽  
Kathrin Hamilton ◽  
Ulrich Steinseifer ◽  
Ivar Friedrich ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Unfractionated Heparin ◽  
Continuous Infusion ◽  
Valve Replacement ◽  
Heart Valves ◽  
Thrombus Formation ◽  
Mechanical Heart Valve ◽  
Mechanical Heart Valves ◽  
Valve Prostheses

SummaryPrevention of valve thrombosis in patients after prosthetic mechanical heart valve replacement and heparin-induced thrombocytopenia (HIT) is still an open issue. The aim of the present in-vitro study was to investigate the efficacy of argatroban and bivalirudin in comparison to unfractionated heparin (UFH) in preventing thrombus formation on mechanical heart valves. Blood (230 ml) from healthy young male volunteers was anticoagulated either by UFH, argatroban bolus, argatroban bolus plus continuous infusion, bivalirudin bolus, or bivalirudin bolus plus continuous infusion. Valve prostheses were placed in a newly developed in-vitro thrombosis tester and exposed to the anticoagulated blood samples. To quantify the thrombi, electron microscopy was performed, and each valve was weighed before and after the experiment. Mean thrombus weight in group 1 (UFH) was 117 + 93 mg, in group 2 (argatroban bolus) 722 + 428 mg, in group 3 (bivalirudin bolus) 758 + 323 mg, in group 4 (argatroban bolus plus continuous infusion) 162 + 98 mg, and in group 5 (bivalirudin bolus plus continuous infusion) 166 + 141 mg (p-value <0.001). Electron microscopy showed increased rates of thrombus formation in groups 2 and 3. Argatroban and bivalirudin were as effective as UFH in preventing thrombus formation on valve prostheses in our in-vitro investigation when they were administered continuously. We hypothesise that continuous infusion of argatroban or bivalirudin are optimal treatment options for patients with HIT after mechanical heart valve replacement for adapting oral to parenteral anticoagulation or vice versa.

Factor Xa Inhibitors for Patients after Mechanical Heart Valve Replacement?

2021 ◽  
Author(s):  
Stephen Gerfer ◽  
Maria Grandoch ◽  
Thorsten C.W. Wahlers ◽  
Elmar W. Kuhn
Keyword(s):  
Heart Valve ◽  
Heart Valves ◽  
Oral Anticoagulants ◽  
Mechanical Heart Valve ◽  
Factor Xa ◽  
Mechanical Heart Valves ◽  
Factor Xa Inhibitors ◽  
Current Evidence ◽  
Small Scale ◽  
Number Of Patients

AbstractPatients with a mechanical heart valve need a lifelong anticoagulation due to the increased risk of valve thrombosis and thrombo-embolism. Currently, vitamin K antagonists (VKA) are the only approved class of oral anticoagulants, but relevant interactions and side effects lead to a large number of patients not achieving the optimal therapeutic target international normalized ration (INR). Therefore, steady measurements of the INR are imperative to ensure potent anticoagulation within a distinctive range. Direct oral anticoagulants (DOACs) with newer agents could serve as a possible alternative to VKAs in this patient cohort. DOACs are approved for several indications, e.g., atrial fibrillation (AF). They only have a minor interaction potential, which is why monitoring is not needed. Thereby, DOACs improve the livability of patients in need of chronical anticoagulation compared with VKAs. In contrast to dual platelet inhibition using aspirin in combination with an ADP receptor antagonist and the direct thrombin inhibitor dabigatran, the oral factor Xa inhibitors apixaban and rivaroxaban show promising results according to current evidence. In small-scale studies, factor Xa inhibitors were able to prevent thrombosis and thrombo-embolic events in patients with mechanical heart valves. Finally, DOACs seem to represent a feasible treatment option in patients with mechanical heart valves, but further studies are needed to evaluate clinical safety. In addition to the ongoing PROACT Xa trial with apixaban in patients after aortic On-X valve implantation, studies in an all-comer collective with rivaroxaban could be promising.

Flow and Thrombosis at Orifices Simulating Mechanical Heart Valve Leakage Regions

2005 ◽  
Vol 128 (1) ◽  
pp. 30-39 ◽  
Author(s):  
Anna M. Fallon ◽  
Nisha Shah ◽  
Ulla M. Marzec ◽  
James N. Warnock ◽  
Ajit P. Yoganathan ◽  
...  
Keyword(s):  
Present Method ◽  
Heart Valves ◽  
Antithrombin Iii ◽  
Thrombus Formation ◽  
Mechanical Heart Valve ◽  
Critical Threshold ◽  
Valve Leakage ◽  
Study Interval ◽  
Flow Through ◽  
Blood Elements

Background: While it is established that mechanical heart valves (MHVs) damage blood elements during leakage and forward flow, the role in thrombus formation of platelet activation by high shear flow geometries remains unclear. In this study, continuously recalcified blood was used to measure the effects of blood flow through orifices, which model MHVs, on the generation of procoagulant thrombin and the resulting formation of thrombus. The contribution of platelets to this process was also assessed. Method of Approach: 200, 400, 800, and 1200μm orifices simulated the hinge region of bileaflet MHVs, and 200, 400, and 800μm wide slits modeled the centerline where the two leaflets meet when the MHV is closed. To assess activation of coagulation during blood recirculation, samples were withdrawn over 0-47min and the plasmas assayed for thrombin-antithrombin-III (TAT) levels. Model geometries were also inspected visually. Results: The 200 and 400μm round orifices induced significant TAT generation and thrombosis over the study interval. In contrast, thrombin generation by the slit orifices, and by the 800 and 1200μm round orifices, was negligible. In additional experiments with nonrecalcified or platelet-depleted blood, TAT levels were markedly reduced versus the studies with fully anticoagulated whole blood (p<0.05). Conclusions: Using the present method, a significant increase in TAT concentration was found for 200 and 400μm orifices, but not 800 and 1200μm orifices, indicating that these flow geometries exhibit a critical threshold for activation of coagulation and resulting formation of thrombus. Markedly lower TAT levels were produced in studies with platelet-depleted blood, documenting a key role for platelets in the thrombotic process.

Computational hemodynamic investigation of a new bileaflet mechanical heart valve

SIMULATION ◽  
2019 ◽  
Vol 96 (5) ◽  
pp. 459-469
Author(s):  
Belkhiri Khellaf ◽  
Boumeddane Boussad
Keyword(s):  
Heart Valve ◽  
Heart Valves ◽  
Stokes Equations ◽  
Thrombus Formation ◽  
Mechanical Heart Valve ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Navier Stokes Equations ◽  
Blood Damage ◽  
Flow Through

In this paper, we perform a numerical analysis for simulating steady, two-dimensional, laminar blood flow through our proposed design, known as the Butterfly mechanical heart valve, where the leaflets are fully opened. Blood has been assumed to be Newtonian and non-Newtonian fluid using the Casson model for shear-thinning behavior. A non-uniform Cartesian grid generation technique is presented to generate a two-dimensional grid for the irregular geometry of the Butterfly valve. The governing Navier–Stokes equations of flow, written in a stream function–vorticity formulation, are solved by the finite difference method with hybrid differencing of the convective terms. The computed results show that the blood’s non-Newtonian nature significantly affects the flow field with the existence of recirculation and consequently stagnation causing thrombus formation, as well as an increase of the shear stress along the wall, which contributes to hemolytic blood damage. The results demonstrate that the model is capable of predicting the hemodynamic features most interesting to physiologists. It can be used to assess thromboembolic problems occurring with heart valves and in the design of cardiac prostheses.

pELAFINT3D: A Unified Approach for Modeling Prosthetic Heart Valves

2013 ◽  
Author(s):  
John A. Mousel ◽  
Sarah C. Vigmostad ◽  
H. S. Udaykumar ◽  
Krishnan B. Chandran
Keyword(s):  
Fine Structure ◽  
Heart Valves ◽  
Thrombus Formation ◽  
Mechanical Heart Valve ◽  
Prosthetic Heart Valves ◽  
Prosthetic Valves ◽  
Valve Motion ◽  
Structure State ◽  
Flow Changes ◽  
Blood Elements

Cutting edge computational tools are an important component of the future of tasks such as surgical planning of mitral valve repair and the design and evaluation of prosthetic valves. For example, despite half a century of use, mechanical heart valves still require further research to reduce the non-physiologic nature of the flow field, which is the source of potential medical complications, of which the most serious complication is thrombus formation [1]. In fact, there is still a lack of consensus in the literature about which flow pathologies are the most damaging to blood elements [2, 3]. Much computational work has been performed examining the flow around mechanical heart valve devices [4, 5], but because the emphasis has been on correct valve motion and not fine structure detail, only the largest features have been adequately resolved and the forward flow structures are allowed to dissipate on stretched meshes such that the features may not lead to the correct fine structure state as directionality of blood flow changes during the cardiac cycle.

scholarly journals TCT CONNECT-347 Overexpansion of Balloon-Expandable Aortic Transcatheter Heart Valves in the Mitral Valve Position

2020 ◽  
Vol 76 (17) ◽  
pp. B149-B150
Author(s):  
Mohammed Al-Hijji ◽  
Mackram Eleid ◽  
Dee Dee Wang ◽  
Susheel Kodali ◽  
Tatiana Kaptzan ◽  
...  
Keyword(s):  
Mitral Valve ◽  
Heart Valves ◽  
Valve Position

scholarly journals Heparin is more effective than apixaban in inhibiting in vitro contact activated coagulation

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
M.M Engelen ◽  
C Van Laer ◽  
M Jacquemin ◽  
C Vandenbriele ◽  
K Peerlinck ◽  
...  
Keyword(s):  
Thrombin Generation ◽  
Heart Valves ◽  
Thrombus Formation ◽  
Oral Anticoagulants ◽  
Direct Oral Anticoagulants ◽  
Factor Xa ◽  
Coagulation Factor ◽  
Mechanical Heart Valves ◽  
Contact Activation

Abstract Introduction Contact of blood with artificial surfaces such as mechanical support devices, catheters, and mechanical heart valves activates the contact activation (CA) pathway of coagulation. Furthermore, recent animal data and clinical studies suggest a more important contribution of CA in pathological thrombus formation in other cardiovascular diseases. Direct oral anticoagulants (DOACs) are recommended as first-line treatment in most patients who require long-term anticoagulation. However, because DOACs directly inhibit a single downstream coagulation factor (thrombin (fXIIa) or factor Xa (fXa)), it has been suggested that their efficacy could be reduced in the presence of strong activation of the CA pathway as compared to anticoagulants that target multiple, more upstream located coagulation factors. Purpose To compare the efficacy of a DOAC (apixaban) and heparin to suppress thrombin generation in the presence of strong CA pathway activation. Methods Pooled platelet-poor plasma was spiked with either apixaban (dissolved in DMSO and PBS) or unfractionated heparin to achieve therapeutic plasma levels. SynthASil, a commercially available mixture of phospholipids and silica, was used to stimulate the CA pathway in two different dilutions (1–80 and 5–80). Downstream coagulation was accessed by Thrombin Generation Test using Thrombinoscope by Stago and associated Thrombin Calibrator (activity 640 nM). The endogenous thrombin potential (area under the thrombin generation curve; ETP), peak thrombin generation (PTG), time to peak (ttPeak) and time to start (ttStart) were accessed. Results With decreasing concentrations of apixaban, stimulation with the lower dose SynthASil reveals an increasing ETP and PTG. As expected, ttPeak and ttStart decreased. Even supratherapeutic levels of apixaban (i.e. 1120 ng/mL) could not inhibit thrombin from being generated, in striking contrast with UFH where no thrombin was formed. Using a five times higher dose of SynthASil showed comparable ETP for all concentrations of apixaban, allocated around the control value. PTG, however, slightly increased with decreasing concentrations of apixaban. ttPeak and ttStart slightly decreased. Except for the subtherapeutic UFH concentration of 0,114 IU/mL, no thrombin was generated with UFH. Conclusion UFH is more effective in inhibiting downstream thrombin generation compared to apixaban as a response to activation of the CA pathway in vitro. These findings could help explain why direct inhibitors were not able to show non-inferiority in patients with mechanical heart valves and support the development of specific CA pathway inhibitors for patients with conditions that activate the CA pathway. Thrombin generation curves Funding Acknowledgement Type of funding source: None

Isothermal Bubble Motion Through a Rotating Liquid

1972 ◽  
Vol 94 (1) ◽  
pp. 187-192 ◽  
Author(s):  
D. L. Schrage ◽  
H. C. Perkins
Keyword(s):  
Radial Direction ◽  
Terminal Velocity ◽  
Distilled Water ◽  
Analytical Prediction ◽  
Bubble Motion ◽  
Large Pressure ◽  
Rotating Liquid ◽  
Angular Velocities ◽  
Large Pressure Gradient ◽  
Good Agreement

An analytical and experimental study of isothermal bubble motion through a liguid which is itself in motion is presented. Both analytical and experimental results are reported for the velocities and trajectories of oxygen bubbles moving through a liquid annulus which is rotating at angular velocities ranging from 500 to 1500 rpm. Results are presented for both distilled water and glycerin. The analytical prediction of the trajectories and velocities showed good agreement with the experimental data. It was found that the bubbles, which were injected at the exterior of the liquid annulus, spiralled inward rapidly and, due to the large pressure gradient in the radial direction, did not reach a constant or terminal velocity.

scholarly journals Adverse Hemodynamic Conditions Associated with Mechanical Heart Valve Leaflet Immobility

2018 ◽  
Vol 5 (3) ◽  
pp. 74 ◽  
Author(s):  
Fardin Khalili ◽  
Peshala Gamage ◽  
Richard Sandler ◽  
Hansen Mansy
Keyword(s):  
Heart Valve ◽  
Heart Valves ◽  
Computational Study ◽  
Cell Damage ◽  
Mechanical Heart Valve ◽  
Flow Characteristics ◽  
Maximal Velocity ◽  
Valve Dysfunction ◽  
Promising Tool ◽  
Artificial Heart Valves

Artificial heart valves may dysfunction, leading to thrombus and/or pannus formations. Computational fluid dynamics is a promising tool for improved understanding of heart valve hemodynamics that quantify detailed flow velocities and turbulent stresses to complement Doppler measurements. This combined information can assist in choosing optimal prosthesis for individual patients, aiding in the development of improved valve designs, and illuminating subtle changes to help guide more timely early intervention of valve dysfunction. In this computational study, flow characteristics around a bileaflet mechanical heart valve were investigated. The study focused on the hemodynamic effects of leaflet immobility, specifically, where one leaflet does not fully open. Results showed that leaflet immobility increased the principal turbulent stresses (up to 400%), and increased forces and moments on both leaflets (up to 600% and 4000%, respectively). These unfavorable conditions elevate the risk of blood cell damage and platelet activation, which are known to cascade to more severe leaflet dysfunction. Leaflet immobility appeared to cause maximal velocity within the lateral orifices. This points to the possible importance of measuring maximal velocity at the lateral orifices by Doppler ultrasound (in addition to the central orifice, which is current practice) to determine accurate pressure gradients as markers of valve dysfunction.

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