4d Echocardiographic Estimation Of Aortic Root Strain In Trileaflet And Bicuspid Aortic Valves
Ankush Aggarwal1, Peter Mortensen1, Jilei Hao2, Lukasz Kaczmarczyk1, Albert T. Cheung3, Lourdes Al Ghofaily2, Robert C. Gorman2, Nimesh D. Desai2, Joseph E. Bavaria2, Alison M. Pouch2.
1University of Glasgow, Glasgow, United Kingdom, 2University of Pennsylvania, Philadelphia, PA, USA, 3Stanford University, Stanford, CA, USA.
OBJECTIVE: Mechanical deformation of the aortic root is conventionally assessed in 2D cross-sectional images, and there is limited knowledge about how cyclic aortic root strain of congenital bicuspid aortic valves (BAVs) differs from physiologically normal aortic valves. We present a framework to estimate regional 3D strains from 4D echocardiography of size-matched roots of minimally calcified BAVs and trileaflet aortic valves (TAVs).
METHODS: A semi-automated image segmentation, shape modeling, and strain analysis pipeline was implemented to analyze deformation of the aortic root in 4D transesophageal echocardiography (Figure 1a). The method is based on fully nonlinear shell-based kinematics, which quantifies in-plane (shear and dilatational) and out-of-plane (thickness) regional strains over the cardiac cycle. Both global and regional strains were characterized in 10 physiologically competent TAVs and 7 minimally calcified BAVs with mean root diameters in the range of 31 - 36 mm. Inter-group differences in TAV and BAV root strain were evaluated using the Wilcoxon rank-sum test.
RESULTS: No statistically significant inter-group differences were observed in global strain measures, which assessed total change in root surface area, root wall volume, and luminal size over the cardiac cycle. Statistically significant differences were observed in localized shear, areal (dilatational), and thickness strains, with higher regional strains in BAV roots. Inter-group differences in the three measures of regional strain were localized to different 3D regions of the aortic root (Figure 1b).
CONCLUSIONS: This study presents a generalizable framework for assessing aortic root strain from volumetric images. The results point to the importance of assessing locally resolved regional deformation in addition to global strain measures. The elevated in-plane and out-of-plane regional strains observed in BAV roots may have implications for future dilatation, dissection, or rupture risk, which warrant further investigation in a large population.
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