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Biomechanics of Aortic ValvesFluid-Structure Interaction Analyses (FSI)

Karin Lavon


Contact:

Karin Lavonkarinlavon@gmail.com


Abstract:

Bicuspid aortic valve (BAV) is the most common type of congenital heart disease, occurring in 0.5-2% of the population, where the aortic valve has only two leaflets rather than the normal three. Calcific aortic valve disease (CAVD) is characterized by stiffened valve leaflets, which rapidly leads to aortic stenosis (AS). BAV patients constitute more than half the patients diagnosed with CAVD, which progresses rapidly compared to tricuspid aortic valves. Transcatheter aortic valve replacement (TAVR) is a treatment approach for CAVD where a stent with mounted bioprosthetic valve is deployed on the stenotic valve. Performing TAVR in calcified BAV patients has only recently been performed off-label, and raise concerns stemming from the asymmetrical structure of the BAV, which can cause partial anchoring and paravalvular leakage (PVL). This research aims to develop and utilize new and refined numerical finite-element simulations for investigating the development of calcification in BAVs, and examine potential percutaneous treatment approaches for those patients, such as balloon aortic valvuloplasty and TAVR.

The clinical part of this study introduces a new Reverse Calcification Technique (RCT) that generates spatial calcified densities from computed tomography (CT) scans of pre-intervention AS patients, and capable of predicting the CAVD progression that leads to the current stage. The different calcification patterns of BAVs were characterized based on acquired CT scans of calcified BAV patients. The CAVD patterns were compared to previous disease stages revealed by the RCT and compared to selected patients who underwent more than one CT procedure in their past.

A new parametric model of type-1 BAV is introduced and serves as a base for modeling diseased BAVs. The RCT method was utilized for a new density-based approach for layered calcification modeling, and a generation of progressive calcified BAV models. Those models were expanded for fluid-structure interaction (FSI) simulations during the full cardiac cycle. Progressive valve stenosis was found to be accompanied by higher jet flow velocities, followed by intense vortices aside from the jet, eventually returning and reaching the calcified leaflets and elevating shear stresses upon them, expediting calcification development.

A calcification fragmentation biomechanical model is introduced to study the balloon-valvuloplasty procedure aimed at expanding AV root and increase compliance. Towards that goal, six stenotic BAVs with varied calcification patterns were modeled. Their calcification fragmentation patterns were revealed by deploying a balloon catheter inside the calcified valves and applying failure criteria for the calcium medium. The geometrical shape of the calcium deposit indicated cracking initiations. Sphere-shaped deposits had a strong resistance to fragmentation compared with arc-shaped deposits, which resulted in multiple crackings in its bottleneck regions, while partial circle pattern deposits remained mostly intact.

The deployments of the two most common FDA-approved TAVR devices inside a calcified BAV, having self and balloon-expandable deployment approaches, were simulated (Evolut and Sapien 3 devices, respectively). The effect of the inner cuff orientation and outer cuff presence on the outcomes of the self-expandable devices were examined by CFD simulations to calculate the paravalvular leakage (PVL) severity. The Evolut stent was characterized in asymmetric and elliptic deployment, with lower anchoring forces compared with the Sapien 3. The Sapien 3 and Evolut PRO had comparable PVL values, while the outer cuff of the Evolut PRO was shown to be more efficient in reducing the leakage compared to the Evolut R. Positioning the Evolut cuff and prosthetic commissures in alignment with the native commissures was found to minimize the PVL.

The proposed clinical and biomechanical computational models in this study are shown to be effective towards BAV patient-specific simulations to improve future treatment in those patients.



Representative Results:























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Education

2016 – 2020 Ph.D. in Mechanical Engineering

Mechanical Engineering School, Engineering Faculty, Tel Aviv University,

Dissertation title: “Biomechanics of Bicuspid Aortic Valves: Fluid-Structure Models Including Calcification and Percutaneous Devices", supervised by Prof. Rami Haj-Ali & Prof. Ehud Raanani


2013 – 2016 M.Sc. in Mechanical Engineering, Magna Cum Laude

Mechanical Engineering School, Engineering Faculty, Tel Aviv University,

Thesis title: "Bio-Mechanical Fluid-Structure Interaction Models of Bicuspid Aortic Valves”, supervised by Prof. Rami Haj-Ali & Prof. Ehud Raanani

• Dean’s award for outstanding achievement, Engineering Faculty


2009 – 2013 B.Sc. in Bio-Medical Engineering,

Bio-Medical Engineering Department, Engineering Faculty, Tel Aviv University



Research Experience

Numerical finite-element simulations of the bicuspid aortic valves (BAV), including fluid-structure interaction (FSI), structural and computational fluid dynamics (CFD) simulations of healthy and pathological BAVs, together with treatment approaches, such as repair and Transcatheter Aortic Valve Replacement (TAVR).


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