FLOW DYNAMIC COMPARISON BETWEEN RECESSED HINGE AND OPEN PIVOT BI-LEAFLET HEART VALVE DESIGNS

Alternative mechanical heart valves for the developing world

Due to the prevalence of rheumatic heart disease in the developing world, mechanical heart valves in the younger patient population remain the prostheses of choice if repair is not feasible. Despite their durability, mechanical valves are burdened by coagulation and thromboembolism. Modern design tools can be utilized during the design process of mechanical valves, which allow a more systematic design approach and more detailed analysis of the blood flow through and around valves. These tools include computer-aided design, manufacturing, and engineering, such as computational fluid dynamics and finite element analysis, modern manufacturing techniques such as additive manufacturing, and sophisticated in-vitro and in-vivo tests. Following this systematic approach, a poppet valve was redesigned and the results demonstrate the benefits of the method. More organized flow patterns and fewer complex fluid structures were observed. The alternative trileaflet valve design has also been identified as a potential solution and, if a similar design approach is adopted, it could lead to the development of an improved mechanical heart valve in the future. It is imperative that researchers in developing countries continue their search for a mechanical heart valve with a reduced thromboembolic risk, requiring less or no anticoagulation.

Influence of Transvalvar Pressure Gradient on Hinge Washing in Closed Mechanical Prosthetic Cardiac Valves Under Pulmonary Pressure Conditions: A Comparative In Vitro Study

OBJECTIVE

Hinge washing is a crucial factor in the prevention of mechanical prosthetic valvar thrombosis, especially in the pulmonary valve position. The aim of this laboratory study was to determine the relationship between pressure difference and the amount of hinge washing in the closed position, using the pressures that are normal for the right ventricle and pulmonary artery.

METHODS

In an in vitro setting, four different bileaflet mechanical valves were tested for hinge washing in closed position. Based on similarity in inner diameter (range: 20.5-21.4 mm), the following valves were tested: Abbott SJM Regent size 23, Cryolife On-X size 23, LivaNova Carbomedics-R size 25, Medtronic Open Pivot (M-OP)-A size 25. Tests were carried out in a range between 3 and 100 mm Hg pressure difference, using water as a test fluid. The amount of leakage per minute through the closed valve was measured.

RESULTS

All four valves showed an increase in leakage with increasing transvalvar gradient, and the relationship between pressure and leakage behaves in logarithmic fashion. Leakage under normal pulmonary diastolic pressure conditions (10 mm Hg) was between 23.3% and 29.3% of the leakage under aortic diastolic pressure conditions (80 mm Hg). The Cryolife On-X valve showed the highest closed leakage volume under pulmonary conditions (10 mm Hg) 0.254 ± 0.01 (L/min), where the Medtronic M-OP showed the lowest leakage volume with 0.125 ± 0.014 (mL/min).

CONCLUSION

Hinge washing is related to transvalvar pressure difference in closed position. Valve brands differed significantly from each other in the amount of hinge washing.

SHEAR-INDUCED PLATELET ACTIVATION IN TORTUOUS CORONARY ARTERY: A NUMERICAL STUDY

High fluid shear stresses (FSSs) were observed in tortuous coronary arteries, especially during the strenuous exercise condition. Whether these high FSSs would enhance the shear-induced platelet activation is still unknown. A computational fluid dynamics (CFD) study was conducted to evaluate the impact of coronary tortuosity (CT) on the shear-induced platelet activation during various conditions. A patient-specific left anterior descending (LAD) coronary artery model (CT model) and the corresponding non tortuous model (nCT model) were reconstructed to perform three-dimensional CFD analysis. Lagrangian particle analysis was performed to further obtain the platelet activation state (PAS) of the platelet-like particles. No significant difference was observed between CT and nCT models on the PAS values reached by the platelet-like particles at all simulated conditions. PAS values for particles within both CT and nCT models were decreased during exercise conditions, as compared to those during the rest condition. These results confirmed that CT could not enhance the platelet activation even with extreme high FSSs existing at bend sections during the strenuous exercise condition, and the results also implied that high FSSs might not be the critical factor leading to the platelet activation during the strenuous exercise for persons without the coronary obstructive.

BOUBAKER POLYNOMIALS EXPRESSION TO THE MAGNETIC PHASE-SHIFT INDUCED IN LEON–VIGMOND 3D-MODEL OF THE HUMAN HEART

The heart is simulated as an electrically controlled fluid pump which operates by mechanical contraction. Human heart modeling is undoubtedly a computationally daunting task which must incorporate magnetic, plastic, mechanic and electric patterns. In this paper, a polynomial mathematical formulation for the magnetic field phase shift in a particular heart 3D-model is proposed. The developed model can give an insight into the local and global complex dynamics of the heart magnetic field under controlled excitation as guides to monitoring i.e., the transition from normal to abnormal myocardial activity or collateral dysfunctions. The used protocol allowed handling the boundary conditions in a smooth way.

Design optimization of a mechanical heart valve for reducing valve thrombogenicity-A case study with ATS valve

Patients implanted with mechanical heart valves (MHV) or with ventricular assist devices that use MHV require mandatory lifelong anticoagulation for secondary stroke prevention. We recently developed a novel Device Thrombogenicity Emulator (DTE) methodology that interfaces numerical and experimental approaches to optimize the thrombogenic performance of the device and reduce the bleeding risk associated with anticoagulation therapy. Device Thrombogenicity Emulator uses stress-loading waveforms in pertinent platelet flow trajectories that are extracted from highly resolved numerical simulations and emulates these flow conditions in a programmable hemodynamic shearing device (HSD) by which platelet activity is measured. We have previously compared two MHV, ATS and the St. Jude Medical, and demonstrated that owing to its nonrecessed hinge design, the ATS valve offers improved thrombogenic performance. In this study, we further optimize the ATS valve thrombogenic performance, by modifying various design features of the valve, intended to achieve reduced thrombogenicity: 1) optimizing the leaflet-housing gap clearance; 2) increasing the effective maximum opening angle of the valve; and 3) introducing a streamlined channel between the leaflet stops of the valve that increases the effective flow area. We have demonstrated that the DTE optimization methodology can be used as test bed for developing devices with significantly improved thombogenic performance.

Role of Computational Simulations in Heart Valve Dynamics and Design of Valvular Prostheses

Computational simulations are playing an increasingly important role in enhancing our understanding of the normal human physiological function, etiology of diseased states, surgical and interventional planning, and in the design and evaluation of artificial implants. Researchers are taking advantage of computational simulations to speed up the initial design of implantable devices before a prototype is developed and hence able to reduce animal experimentation for the functional evaluation of the devices under development. A review of the reported studies to date relevant to the simulation of the native and prosthetic heart valve dynamics is the subject of the present paper. Potential future directions toward multi-scale simulation studies for our further understanding of the physiology and pathophysiology of heart valve dynamics and valvular implants are also discussed.