Altered aortic shape in bicuspid aortic valve relatives influences blood flow patterns

Abstract

Aims: Bicuspid aortic valve (BAV) is known to exhibit familial inheritance and is associated with aortopathy and altered aortic haemodynamics. However, it remains unclear whether BAV-related aortopathy can be inherited independently of valve morphology.

Methods and results: Four-dimensional flow magnetic resonance imaging for the in vivo assessment of thoracic aortic 3D blood flow was performed in 24 BAV relatives with trileaflet aortic valves (age = 40 ± 14 years) and 15 healthy controls (age = 37 ± 10 years). Data analysis included aortic dimensions, shape (round/gothic/cubic), and 3D blood flow characteristics (semi-quantitative vortex/helix grading and peak velocities). Cubic and gothic aortic shapes were markedly more prevalent in BAV relatives compared with controls (38 vs. 7%). Ascending aorta (AAo) vortex flow in BAV relatives was significantly increased compared with controls (grading = 1.5 ± 1.0 vs. 0.6 ± 0.9, P = 0.015). Aortic haemodynamics were influenced by aortic shape: peak velocities were reduced for gothic aortas vs. round aortas (P = 0.003); vortex flow was increased for cubic aortas in the AAo (P < 0.001) and aortic arch (P = 0.004); vortex and helix flows were elevated for gothic aortas in the AAo and descending aorta (P = 0.003, P = 0.029). Logistic regression demonstrated significant associations of shape with severity of vortex flow in AAo (P < 0.001) and aortic arch (P = 0.016) in BAV relatives.

Conclusion: BAV relatives expressed altered aortic shape and increased vortex flow despite the absence of valvular disease or aortic dilatation. These data suggest a heritable component of BAV-related aortopathy affecting aortic shape and aberrant blood flow, independent of valve morphology.

Keywords: 4D flow MRI; bicuspid aortic valve; haemodynamics; relatives.

Figure 1

(A) Locations for diameter measurements along the aorta (Subject 3, Family 1): (1) SOV, (2) sinotubular junction (STJ), (3) mid-AAo at the level of right pulmonary artery (MAA), (4) proximal aortic arch immediately proximal to brachiocephalic trunk (PROX), (5) aortic arch between the left common carotid and subclavian arteries (ARCH), (6) distal aortic arch immediately distal to left subclavian artery (DIST), and (7) DAo at the level of left atrium (DESC). (B) Measurement of aorta width and height for calculating the width-to-height ratio.

Figure 2

Velocity MIP for BAV relatives with round (normal), cubic, and gothic aortas. The white arrow in the gothic aorta points the acute angulation between AAo and DAo with the horizontal part of the aorta being shortened. Differences in blood flow velocities for different shapes are clearly evident.

Figure 3

Examples of helix (top row) and vortex (bottom row) flows visualized using velocity-colour-coded 3D streamlines (red = fast velocities and blue = slow, see legend on the left) at peak systole. From left to right, the degree of vortex and helix flows increases from mild to severe. The left panel shows an example without helix or vortex flow. The white arrows point to the particular area of vortex or helix flow. Both the mild and severe helix examples had similar degrees of vortex flow.

Figure 4

Family trees of all seven BAV families showing all relatives with a tricuspid aortic valve without colour filling, all known kindred, but with unknown valve morphology with a grey filling and all BAV cases with black filling. According to the standardized human pedigree nomenclature, females are represented with a circle, males with a square, and unknown gender with a diamond.

Figure 5

Results of semi-quantitative flow pattern grading. Significant differences (P < 0.05) between controls, BAV relatives, and FDRs as well as between round and cubic and round and gothic are indicated with an asterisk. (A) Vortex flow for AAo, aortic arch, and DAo. (B) Helix flow for AAo, arch, and Dao. (C) Occurrence of vortex flow for round, cubic, and gothic aortas. (D) Occurrence of helix flow in round, cubic, and gothic aortas.