4D Computed Tomography Analysis of the Bicuspid Aortic Valve

Abstract

Objectives: To evaluate the role of 4D (3D+time) analysis using multiphase cardiac computed tomography (MCCT) in the description of the aortic annulus (AA) of bicuspid aortic valves (BAV) with regards to the latest expert consensus classification. Methods: ECG-gated MCCT of 15 patients with BAV were analyzed using an in-house software and compared to 15 patients with normal tricuspid aortic valve (TAV). The AA border was pinpointed on 9 reconstructed planes and the 3D coordinates of the 18 consecutive points were interpolated in 3D using a cubic spline to calculate 3D areas, perimeters, diameters, eccentricity indexes and global height. Measurements were repeated through the cardiac cycle (10 phases). Three additional planes were generated at the level of the left ventricular outflow tract (LVOT), the Valsalva sinuses and the sinotubular junction (STJ). Results: The annulus area was significantly larger in BAV than in TAV (Mean indexed 3D area 5.64±0.84 cm²/m2 vs 4.3±0.38 cm²/m² respectively, < 0.001). The AA was also larger in BAV than in TAV in terms of perimeter, diameters, and height (p<0.001). The Valsalva sinuses and the STJ were also significantly larger in BAV compared to TAV (mean area in end-diastole of 6.06±1.00 cm² vs 4.69±1.00 cm², p<0.001 and 5.13±1.62 cm² vs 3.62±0.99 cm², p<0.001 respectively). In BAV, 3D AA shape analysis helps to distinguish the 3 types of BAV: the 2-sinus type (symmetrical), the fused type, and the partial-fusion type or “form fruste” (both asymmetrical). It also allows to determine the position and the height of the nonfunctional commissure. In symmetrical BAV, the non-functional commissure was significantly lower than the other commissures (6.01±4.27mm vs 18.24±3.20mm vs 17.15±3.60mm, p <0.001) whereas in asymmetrical BAV, the 3 commissures had comparable heights (16.38±0.86mm vs 15.88±1.69mm vs 15.37±0.88mm, p=0.316). There was no difference in AA eccentricity indexes between TAV and BAV in all phases of the cardiac cycle. However, there was a spectrum of ellipticity for the other components of the aortic root between the different types of valves: going from TAV to asymmetrical BAV to symmetrical BAV, at end-diastole, the LVOT became more circular, and the Valsalva sinuses became more elliptical. Conclusion: 3D morphometric analysis of the BAV using MCCT allows to identify the type of BAV, and to describe the position and height of the nonfunctional commissure. There are significant differences in the morphology of the aortic root between TAV and the different types of BAV. Further studies should be done to evaluate the impact of 3D analysis on the procedural planning of pathological BAV.