Aortic annulus sizing by CT. (a): The anterior-posterior (AP) (D3) and mediolateral diameter (ML) (D4) are measured on cross-sectional images. The mean of both diameters is commonly calculated for selecting the appropriate size of the transcatheter aortic valve prosthesis device finally used for TAVI (currently, 23 mm, 26 mm, or 29 mm devices). Exact fit is crucial to avoid paravalvular leakage and to ensure seamless adaption of the prosthesis with the aortic annulus. (b): Quantification of the annulus area is another valuable parameter for selection of the final valve size. Aortic annulus area is traced with a digital caliper (Area, 475 mm2).
