A simplified D-shaped model of the mitral annulus to facilitate CT-based sizing before transcatheter mitral valve implantation

Background: The nonplanar, saddle-shaped structure of the mitral annulus has been well established through decades of anatomic and echocardiographic study. Its relevance for mitral annular assessment for transcatheter mitral valve implantation is uncertain. Objective: Our objectives are to define the methodology for CT-based simplified "D-shaped" mitral annular assessment for transcatheter mitral valve implantation and compare these measurements to traditional "saddle-shaped" mitral annular assessment. Methods: The annular contour was manually segmented, and fibrous trigones were identified using electrocardiogram-gated diastolic CT data sets of 28 patients with severe functional mitral regurgitation, yielding annular perimeter, projected area, trigone-to-trigone (TT) distance, and septal-lateral distance. In contrast to the traditional saddle-shaped annulus, the D-shaped annulus was defined as being limited anteriorly by the TT distance, excluding the aortomitral continuity. Hypothetical left ventricular outflow tract (LVOT) clearance was assessed. Results: Projected area, perimeter, and septal-lateral distance were found to be significantly smaller for the D-shaped annulus (11.2 ± 2.7 vs 13.0 ± 3.0cm²; 124.1 ± 15.1 vs 136.0 ± 15.5mm; and 32.1 ± 4.0 vs 40.1 ± 4.9mm, respectively; P < .001). TT distances were identical (32.7 ± 4.1mm). Hypothetical LVOT clearance was significantly lower for the saddle-shaped annulus than for the D-shaped annulus (10.7 ± 2.2 vs 17.5 ± 3.0mm; P < .001). Conclusion: By truncating the anterior horn of the saddle-shaped annular contour at the TT distance, the resulting more planar and smaller D-shaped annulus projects less onto the LVOT, yielding a significantly larger hypothetical LVOT clearance than the saddle-shaped approach. CT-based mitral annular assessment may aid preprocedural sizing, ensuring appropriate patient and device selection.