(181m) Computational Fluid Dynamics (CFD) Assessment of Native Stenotic Aortic Valve Employing In Vivo Computed Tomography (CT) Derived Geometries

Currently, in developed countries, 2% of people about age 65 and 4% of people above age 80 have aortic stenosis. Aortic stenosis is a heart valve disorder that narrows or obstructs the aortic valve (AV) opening.   The diagnosis of aortic stenosis is complicated by the elastic composite material construction of the arterial system, wide variation in geometrical properties, and coupled pulsatile and peristaltic behavior of the cardiovascular system.  The key to diagnosis is to utilize limited available data from clinical measurement to produce an accurate assessment on whether or not a patient with other medical obstacles can 1) survive the valve replacement operation and 2) live longer after surgery than if they continued with their original valve. 

In the 60 years that has passed since the publication of the Gorlin formula which has been employed widely in clinical diagnosis of heart valve diseases, various medical imaging technologies have been developed that allow us to obtain more information about in vivo geometries and turbulent flows around the heart valve.  In this study, dimensions of the aortic valve and its root were derived from an intravenous contrast enhanced retrospectively ECG gated multidetector CT (64-slice Philips Brilliance 64) axial data set. CT data permitted reconstruction of the in vivo geometry using commercially available software packages of Materialise Mimics 14.01 and 3-Matic 5.1. Pro/Engineer was used to generate artificial orifice geometries with maintained sinus structure and to limit modifications to the orifice geometry only. A Casson non-Newtonian fluid model was employed in the CFD study via ANSYS CFX.

The current study re-examines the validity of Gorlin formula when applied on CT derived in vivo geometry of a patient with severe aortic stenosis, using CFD simulation, as well as its validity in artificial, computer generated valve orifice geometries. The empirically derived Gorlin formula is assumed to be independent of flow rate; however, this computational study shows that the Gorlin formula is dependent not only on the flow rate but also on the three-dimensional geometrical variations.