Deformation Dynamics and Mechanical Properties of the Aortic Annulus by 4-Dimensional Computed Tomography: Insights Into the Functional Anatomy of the Aortic Valve Complex and Implications for Transcatheter Aortic Valve Therapy

Objectives rpose of this study was to assess deformation dynamics and in vivo mechanical properties of the aortic annulus throughout the cardiac cycle. ound tanding dynamic aspects of functional aortic valve anatomy is important for beating-heart transcatheter aortic valve implantation. s -five patients with aortic stenosis and 11 normal subjects underwent 256-slice computed tomography. The aortic annulus plane was reconstructed in 10% increments over the cardiac cycle. For each phase, minimum diameter, ellipticity index, cross-sectional area (CSA), and perimeter (Perim) were measured. In a subset of 10 patients, Youngʹs elastic module was calculated from the stress-strain relationship of the annulus. s h subjects with normal and with calcified aortic valves, minimum diameter increased in systole (12.3 ± 7.3% and 9.8 ± 3.4%, respectively; p < 0.001), and ellipticity index decreased (12.7 ± 8.8% and 10.3 ± 2.7%, respectively; p < 0.001). The 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). Accordingly, relative percentage differences between maximum and minimum values were significantly smallest for Perim compared with all other parameters. Youngʹs modulus was calculated as 22.6 ± 9.2 MPa in patients and 13.8 ± 6.4 MPa in normal subjects. sions rtic 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 valves, because tissue properties allow very little expansion. Aortic annulus perimeter appears therefore ideally suited for accurate sizing in transcatheter aortic valve implantation.