Abstract 9644: Deformation Dynamics and Mechanical Properties of the Aortic Annulus by Four-Dimensional Computed Tomography Insights Into the Functional Anatomy of the Aortic Valve Complex and Implications for Transcatheter Aortic Valve Therapy

Abstract

Objectives: To assess deformation dynamics and mechanical properties of the aortic annulus. Background: Understanding dynamic aspects of functional aortic valve anatomy is important for beating-heart transcatheter aortic valve implantation (TAVI). Methods: Thirty five patients with aortic stenosis and eleven normal subjects underwent 256-slice computed tomography (CT). The aortic annulus plane was reconstructed in 10% increments of the RR-interval. For each phase minimum diameter (Min), ellipticity index (EI), cross-sectional area (CSA), and perimeter (Perim) were measured (Figure 1). In a subset of 10 patients Young's elastic module was calculated from the stress-strain relationship of the annulus. Results: In both subjects with normal and with calcified aortic valves Min increased in systole (12.3 ± 7.3% and 9.8 ± 3.4%, respectively; P < 0.001) and EI decreased (12.7 ± 8.8% and 10.3 ± 2.7%; P < 0.001, respectively). CSA increased by 11.2 ± 5.4% and 6.2 ± 4.8, respectively (P < 0.001). Perim increase was negligible in patients with calcified valves (0.56 ± 0.85%; P < 0.001) and small even in normal subjects (2.2 ± 2.2%; P = 0.01). Young's modulus was calculated as 13.2 MPa in patients. Kolmogorov-Smirnov analysis, showed significant differences between maximum and minimum values for all parameters except perimeter. Conclusion: The aortic annulus, generally elliptic, assumes a more round shape in systole, thus increasing CSA without substantial change in perimeter. Perimeter changes are negligible in patients with calcified valve, because tissue properties allow very little expansion. Figure 1: Reconstruction of the aortic annulus from the sagittal (A) and the coronal planes (B). The aortic annulus is defined as the circumferential connection of the aortic leaflets' most basal attachments in the reconstructed axial plane (C). Measurements of the minimum and maximum diameter (D), the perimeter (E), and the area (F) were performed in this plane.