ASCENDING AORTA FLOW: INFLUENCE OF ARTIFICIAL HEART VALVES

Cooperative study
TU-Graz, Inst. of Mathematics: A. Leuprecht, K. Perktold
ETH and Uni-Zürich, Inst. of Biomed. Engineering: S. Kozerke, P. Boesiger

Flow dynamic details in the ascending aorta downstream of native and prosthetic aortic valves are of great interest.

The highly convective nature of blood flow in the ascending aorta results in very thin boundary layers which cannot be resolved with appropriate resolution by current MRI systems. Numerical simulation can be carried out at a scale beyond the resolution limit of MRI in-vivo.

The flow simulation is based on in-vivo MR data concerning time-varying vessel geometry and inflow condition (inflow velocity profiles).

ASCENDING AORTA: Computational model, based on time-varying geometric data acquired from MRI scans



Bileaflet mechanical valve - Saint Jude Medical


Native configuration - MRI measurements in a normal volunteer subject
Artificial valve configuration - in a patient with a bileaflet mechanical valve implanted in the aortic position


AXIAL VELOCITY PROFILES at systolic peak flow



Native valve - "Flat" profiles, skewing to the inner wall of the aortic arch (blue: measured MRI data)



Valve prosthesis - Two jets corresponding to the orifices of the valve, skewing to the posterior wall (blue: measured MRI data)


Highly convective flow ® thin boundary layers

IN-PLANE STREAMTRACES


at the outflow cross-section F

Native valve
Valve prosthesis


AXIAL WALL SHEAR STRESS


Native valve
Valve prosthesis


Axial WSS is higher downstream of the aortic valve prosthesis when compared to the native configuration

CONCLUSION


Combining CFD and MRI appears to be a promising tool for studying fluid dynamics connected with cardiovascular implants. This method potentially extends the quantification of flow dynamic variables in-vivo at a scale beyond the resolution limit of MRI.

The approach might offer a relatively new way towards an improved assessment of detailed in-vivo flow conditions and alterations of blood flow associated with heart valve prostheses.

Knowledge of fluid dynamic details should be helpful to develop optimum design of implants to further improve their in-vivo performance.

Comparison between native and mechanical bileaflet valve configuration:

Abdominal aorta inflow is different

Ş Strong consequences on flow and WSS patterns in the abdominal aorta

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