Bicuspid aortic valve annulus: assessment of geometry and size changes during the cardiac cycle as measured with a standardized method to define the annular plane

Abstract

Purpose: Bicuspid aortic valve (BAV) is a complex malformation affecting not merely the aortic valve. However, little is known regarding the dynamic physiology of the aortic annulus in these patients and whether it is similar to tricuspid aortic valves (TAV). Determining the BAV annular plane is more challenging than for TAV. Our aim was to present a standardized methodology to determine BAV annulus and investigate its changes in shape and dimensions during the cardiac cycle.

Methods: BAV patients were prospectively included and underwent an ECG-gated cardiac CTA. The annulus plane was manually identified on reconstructions at 5% intervals of the cardiac cycle with a new standardized method for different BAV types. Based on semi-automatically defined contours, maximum and minimum diameter, area, area-derived diameter, perimeter, asymmetry ratio (AR), and relative area were calculated. Differences of dynamic annular parameters were assessed also per BAV type.

Results: Of the 55 patients included (38.4 ± 13.3 years; 58% males), 38 had BAV Sievers type 1, 10 type 0, and 7 type 2. The minimum diameter, perimeter, area, and area-derived diameter were significantly higher in systole than in diastole with a relative change of 13.7%, 4.8%, 13.7%, and 7.2% respectively (all p < 0.001). The AR was ≥ 1.1 in all phases, indicating an elliptic shape, with more pronounced flattening in diastole (p < 0.001). Different BAV types showed comparable dynamic changes.

Conclusions: BAV annulus undergo significant changes in shape during the cardiac cycle with a wider area in systole and a more elliptic conformation in diastole regardless of valve type.

Key points: • A refined method for the identification of the annulus plane on CT scans of patients with bicuspid aortic valves, tailored for the specific anatomy of each valve type, is proposed. • The annulus of patients with bicuspid aortic valves undergoes significant changes during the cardiac cycle with a wider area and more circular shape in systole regardless of valve type. • As compared to previously published data, the bicuspid aortic valve annulus has physiological dynamics similar to that encountered in tricuspid valves but with overall larger dimensions.

Keywords: Bicuspid aortic valve; Cardiovascular physiological phenomena; Computed tomography angiography; Cross-sectional anatomy; Transcatheter aortic valve replacement.

Fig. 1

Determination of the annulus in patients with BAV type 1 with asymmetric cusps. (a) Volume rendered (VR) reconstructions in systole (a1) and diastole (a2) demonstrating the asymmetry of the sinuses due to the smaller dimensions of the right coronary cusp (RCC) (arrows). (b–d) Wrong annulus plane definition based on the three hinge points. In (b1) and (c1) schematic representations of the LVOT, sinuses of Valsalva (red, yellow, blue lines) and sinotubular junction (gray line) where the annulus plane (green line) was identified as the plane passing through the three hinge points (hinge point of the RCC in red; hinge point of the non-coronary cusp (NCC) in blue; hinge point of the left coronary cusp (LCC) in yellow). In (b2–b3) and (c2–c3), VR reconstructions showing the angulation between the centerline passing through the LVOT/aortic root and the line (b2–b3 and c2–c3; green lines) passing through the hinge points of the LCC and the NCC (b) and RCC (c), respectively. In (d1) and (d2), MPR showing the position of the axis in the longitudinal planes when identifying the plane passing through the three hinge points (d3). (e–f) Correct annulus plane definition. At first, one plane passing through the two hinge points of the two biggest cusps is identified (e1); then, this plane is tilted along the only still undetermined direction (e2) until the minimum cross-sectional area and/or a plane perpendicular to the centerline is obtained (e3). In (f1) and (f2), MPR showing the position of the axis in the longitudinal planes when determining the plane passing through the two hinge points and then make adjustments by tilting the violet and orange axis to identify the smallest possible area and a plane perpendicular to the centerline (e3)

Fig. 2

Determination of the annulus plane in patients with BAV type 0. (a) VR reconstructions in systole (a1) and diastole (a2) showing the presence of only two cusps. (b) 3D anatomy of the aortic root. (c–d) One plane passing through the two hinge points of the two cusps is defined (c1); then, this plane is tilted along the only still undetermined direction (c2) until the minimum cross-sectional area and/or a plane perpendicular to the centerline is obtained (c3). In (d1) and (d2), MPR showing the position of the axis in the longitudinal planes when determining the annulus plane (d3) as detailed above

Fig. 3

Annulus measurements. (a) Measurement of the annulus parameters (maximum and minimum diameters, perimeter, area, and area-derived diameter) based on the semi-automatically defined contour. (b) A case example showing all the 20 phases analyzed in a patient with BAV type 1 LR. The annulus shows a more circular shape in systole and a more elliptic shape during diastole

Fig. 4

Mean annulus parameters per cardiac phase. Vertical bars indicate 95% confidence intervals (CI)

Fig. 5

Mean AR and RA per phase and valve type. Vertical bars indicate 95% CI

Fig. 6

Asymmetry ratio and relative area in groups with different heart rates during successive phases of the cardiac cycle expressed in terms of percentage (a and b) and absolute time (c and d)