Author + information
- Ryo Torii, PhD,
- Maria Kalantzi, MD,
- Stergios Theodoropoulos, MD,
- Padmini Sarathchandra, PhD,
- Xiao Yun Xu, PhD and
- Magdi H. Yacoub, MD∗ ()
- ↵∗Harefield Heart Science Centre, Hill End Road, Harefield, Middlesex UB9 6JH, United Kingdom.
Bicuspid aortic valve (BAV) is the most common congenital cardiac anomaly with a prevalence of 1% to 2% in the general populations. Acute dissection and rupture of the ascending aorta in patients of aortic stenosis due to BAV carries very poor prognosis. The aortic wall abnormality is known to be an integral part of the BAV syndrome. The changes in the aortic wall are known to be due to several causes including genetic, developmental and hemodynamic factors (1). However, while significant efforts have been devoted to elucidating the genetic and developmental aspects, the effect of hemodynamic factors has been less adequately defined despite some recent attempts made in imaging and/or computational approaches (2). Previous flow studies focused on characterizing aortic flow patterns and quantified hemodynamic shear stress (3). However, the all-important changes in the structure of the aortic wall and their causes (4) have not been adequately studied in patients with BAV. Here, we describe a patient in whom an extensive damage of the aortic wall is colocalized with hemodynamic jet impact, using a noninvasive technique that could also be used to predict damage to the aortic wall.
A male patient, 46 years of age, presented with symptomatic aortic valve stenosis due to a BAV with fusion of right and noncoronary cusps (Fig. 1A). In an attempt to define the degree of dilation of ascending aorta and characterize flow dynamics in the aortic root, magnetic resonance imaging using 1.5-T clinical scanner was performed. Breath-holding and electrocardiography-gated sequence with contrast agent was used to acquire bright blood transversal images from the thorax at 2.5 mm interval (0.703 mm/pixel in-plane resolution). Phase-contrast images were also acquired at mid-sinus level (5.0 mm slice thickness and 1.328 mm/pixel in-plane resolution) at 20 timings during the cardiac cycle using breath-holding and electrocardiography-gated sequence with 450 cm/s of encoding velocity.
The acquired anatomical images were segmented in reference to image intensity to reconstruct vascular anatomy in 3D. Spatiotemporal evolution of the blood flow in the aorta as well as wall shear stress were calculated using computational fluid dynamics (CFD) using the reconstructed anatomical model and the cross-sectional, through-plane velocity profile based on phase-contrast magnetic resonance images. Here, the anatomical model was truncated at the mid-sinus level and the spatiotemporal velocity profile was mapped as boundary conditions. The aortic wall was assumed to be rigid and no turbulence model was used. The assumptions potentially lead to the shear stress value overestimated but in the condition of the present study, the aortic anatomy and inflow condition are expected to be more dominant. Details of the procedure, including quality control of computational mesh, can be found in our previous papers (5).
A hemodynamic jet through the stenosed valve with 4.46 m/s was measured which impinged on a localized area of the outer-curvature of the ascending aorta. Stress mapping of this region showed endothelial shear stress of 18.56 Pa, which could be extremely damaging over time with progressive thinning of the aorta (Fig. 1B). Per operative and histological observation showed a localized area of extreme aortic wall thinning: 390 μm in thickness with complete interruption of the media and absence of elastic fibers and smooth muscle cells, which were compatible with impending rupture (Fig. 1B). The aortic wall in this area was represented by a thinned-out adventitia layer. Even in the thicker part of the wall, there were areas devoid of elastic fibers and smooth muscle cells indicating the loss of normal lamellar organization of alternative layers of elastic fibers, smooth muscle cells, and collagen. This area corresponded to the area defined by magnetic resonance imaging and CFD as being impinged on by an extremely fast jet. The aneurysmal aorta measuring 7.5 cm in diameter was excised and was replaced with a Dacron graft (Hemashield, Boston Scientific, Natick, Massachusetts) 30 mm in diameter. The aortic valve, which was extremely heavily calcified, was replaced with 27 Freestyle porcine xenograft root (Medtronic, Inc., Minneapolis, Minnesota).
Post-operative magnetic resonance imaging and CFD were performed 13 months after operation using exactly the same method as pre-operatively, except for encoding velocity in phase-contrast MR acquisition (Venc = 200 cm/s). The result showed smooth flow pattern in the aortic root, along the ascending aorta and arch without any jet (maximum velocity 1.43 m/s). The maximal level of endothelial shear stress was 5.32 Pa, which falls within the normal limits.
This case demonstrates that abnormal hemodynamics can lead to severe localized structural damage to the aortic wall.
For supplemental videos, please see the online version of this article.
Please note: Dr. Torii was supported as a Qatar Cardiovascular Research Center Fellow by The Qatar Foundation. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- American College of Cardiology Foundation
- Barker A.J.,
- Markl M.,
- Burk J.,
- et al.
- Tan F.P.P.,
- Xu X.Y.,
- Torii R.,
- et al.