Blood flow patterns in patients with bicuspid aortic valve undergoing different type of aortic valve replacement-computational fluid dynamics analyses and case reports

Introduction

Background

The bicuspid aortic valve (BAV) is a frequently seen congenital heart defect in adults, affecting approximately nearly 1% of the population worldwide (1). The BAV is frequently associated with the ascending aortic dilation. This condition, called bicuspid aortopathy, may lead to serious clinical consequences such as aortic aneurysm, dissection, or rupture (2,3). Current guidelines recommend prophylactic repair or replacement of ascending aorta in BAV patients when the diameter exceeds 45 mm during the aortic valve surgery (4,5). Surgical aortic valve replacement (SAVR) remains the first-line therapy for patients who can tolerate open heart surgery, although the indication for transcatheter aortic valve replacement (TAVR) continues to expand.

Rationale and knowledge gap

Hemodynamic abnormality plays an important role in the ascending aortic dilation (6). Computation fluid dynamics (CFD) is useful for assessment of hemodynamics. It allows visualization of the blood flow streamline (7). Disturbed flow patterns, such as flow eccentricity and helicity, have been associated with asymmetric wall stress and region-specific dilation of the ascending aorta (8). The wall shear stress (WSS) and the aortic pressure because these hemodynamic parameters play a critical role in the pathophysiology of ascending aortic dilation. Abnormal WSS has been shown to promote extracellular matrix degradation and medial degeneration (6-8). Similarly, altered pressure distribution also contributes to increased wall tension (6-8). Although previous studies have shown that blood flow patterns might be associated with aortic dilation and adverse aortic events (9,10), studies regarding the comparison of different types of aortic prostheses are limited.

Objective

The present study aimed to compare the hemodynamics in BAV patient with ascending aortic dilation who underwent aortic valve replacement (AVR). We focused on the WSS, pressure, and flow patterns because these parameters were reported to be associated with ascending aortic dilation (6,8). We also sought to compare these hemodynamic parameters between different types of AVR. We present this article in accordance with the CARE reporting checklist (available at https://cdt.amegroups.com/article/view/10.21037/cdt-2025-1-643/rc).

Case presentation

Study patients

We identified three BAV patients with severe aortic stenosis with ascending aortic dilation (maximum diameter ≥40 mm) who underwent mechanical AVR, bioprosthetic AVR, and TAVR, respectively. All patients underwent uneventful operations. We performed CFD analyses for these patients using pre- and post-operative computed tomography angiography (CTA) data. All procedures performed in this study were in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the institutional review board of Fuwai Hospital (date of review, 24 February 2025; approval No. 2025-2627). Written informed consent was obtained from the patients for the publication of this case report. A copy of the written consent is available for review by the editorial office of this journal.

Geometric model and mesh generation

The luminal geometries were derived from CTA images using the Materialise Mimics 21.0 (Leuven, Belgium). The three-dimensional aorta models were created using Digital Imaging and Communications in Medicine (DICOM) data. The geometric model of the prosthetic valve was derived from postoperative CTA images and virtually placed at the appropriate location within the reconstructed aortic model. All valves were modeled in the fully open position to simulate systolic flow conditions.

For the mechanical valve, we segmented the housing and leaflets based on Hounsfield unit thresholds. The leaflets were oriented at a 25° angle relative to the valve housing, which matches the fully open configuration of typical bileaflet mechanical valves. The sewing ring was included as a simplified annular structure, using dimensional specifications provided by the manufacturer.

For the bioprosthetic valve, stent posts were clearly visible on CTA, but leaflet tissue itself fell below the resolution limit of clinical CT. We therefore reconstructed leaflet geometry using the stent frame topology, alongside anatomical references from published literature on leaflet attachment sites and free-edge geometry (9). The sewing ring was modeled as an integral part of the stent structure.

For the TAVR valve, we segmented the nitinol frame from CTA via gradient-based edge detection. Anatomical positioning was determined using radiopaque markers, and we verified proper apposition to the native aortic annulus. Leaflet geometry was modeled similarly to the bioprosthetic valve, with dimensions adjusted to match the device’s specific design.

We validated virtual implantation with the input of an experienced cardiac surgeon (Dr. K.A.), who compared the model directly to intraoperative records and multiplanar reformats from postoperative imaging.

Computational meshes corresponding to the reconstructed three-dimensional aortic models were constructed via the commercial grid-generation software ANSYS^®-ICEM CFD 2025 (ANSYS, Inc., Canonsburg, PA, USA) for discretization of the computational domain. To ensure the reliability of CFD results, a systematic grid independence analysis was conducted based on WSS, a key hemodynamic parameter of interest. Four mesh densities were evaluated: 1.0 million, 1.5 million, 2.0 million, and 2.5 million elements. Grid refinement was stopped when the relative difference in mean WSS across the ascending aortic wall between successive mesh densities was less than 5%. The final mesh, comprising approximately 2.0 million tetrahedral elements and five prismatic layers, was chosen to balance computational accuracy and efficiency.

Boundary conditions

Blood flow was modeled as an incompressible Newtonian fluid with a density of 1.06×10³ kg/m³ and a viscosity of 3.5×10⁻³ Pa·s. Blood flow was assumed to be laminar, and no turbulence model was applied. Our choice of Newtonian model is supported by practical and academic evidence relevant to the present study (11,12). The ascending aorta is a high-shear environment where shear rates consistently exceed 100 s⁻¹. In such environments, blood’s shear-thinning properties are barely noticeable, and its viscosity tends to stabilize at a constant value—this makes the Newtonian assumption highly applicable. Notably, in stenotic regions, the already elevated shear rates further weaken non-Newtonian effects, which reinforces the rationality of our model. Additionally, our study focuses on global hemodynamic parameters post-AVR, such as pressure distribution and bulk flow patterns. While non-Newtonian behavior might affect local flow in low-shear areas (e.g., sinus vortices), it has little impact on the macroscopic measures that are the core of our analysis. We also aligned our modeling with clinical data: inlet boundary conditions were derived from transthoracic echocardiography, which captures bulk flow and reflects blood’s macroscopic properties—in turn ensuring consistency between our computational model and clinical observations.

As described above, the inlet flow velocity profiles at the orifice of the native aortic valve (pre-operative) or the prosthetic valve (post-operative) were acquired by echocardiography in real time with electrocardiogram. The outlet boundaries included innominate artery, left carotid artery, left subclavian artery, and descending aorta, where a zero pressure condition was applied. The blood flow stimulation was run for 3 cardiac cycles. Time step was set to 1×10⁻⁴ s to capture the hemodynamic changes. It satisfies the Courant-Friedrichs-Lewy (CFL) condition, which is critical for capturing systolic hemodynamics—where flow accelerates rapidly. From our mesh independence study, we established a near-wall resolution of 0.01 mm. Combined with typical aortic velocities, this time step keeps the maximum CFL number below 1.0 across the entire domain, ensuring both numerical stability and sufficient temporal resolution for flow features. The convergence criterion was set to 1×10⁻⁵ for all residual variables. Specifically, this criterion was applied to all normalized residuals of the solved equations in the ANSYS^®-FLUENT 2025 framework, including continuity (mass conservation), momentum equations in all three coordinate directions, and relevant turbulence equations. This ensures the full convergence of all flow field variables—pressure, velocity components, and turbulence parameters—at each time step. To ensure the stability and periodicity of the transient simulation results, the blood flow simulation was run for 3 complete cardiac cycles. Data from the first cycle were discarded due to the influence of initial conditions, and data from the third cycle were finally used for hemodynamic analyses. The blood flow simulation and analyses were employed using the ANSYS FLUENT 16.2 (ANSYS, Inc.).

Hemodynamic results

Baseline patient characteristics were shown in Table 1. All patients had type-1 left/right (L/R) BAV with ascending aortic dilation (maximum diameter ≥40 mm). All had uneventful operations and underwent pre- and post-operative CTA and echocardiography.

Figure 1 demonstrated the CFD analyses for mechanical AVR. Before the procedure, the patient had abnormal right-handed helical flow pattern. The peak velocity and the mean pressure gradient were 5.1 m/s and 59 mmHg, respectively. The highest pressure and the WSS was in the right anterior position which corresponds to the great outer curvature. After the procedure, the blood flow patterns improved. The peak velocity and the mean pressure gradient were 1.7 m/s and 7 mmHg, respectively. The pressure and the WSS also drastically decreased (pressure from 19,806 to 16,718 Pa, WSS from 89 to 17 Pa).

Figure 1 Representative of computational fluid dynamic-generated flow patterns in patient 1 (mechanical valve).

Figure 2 demonstrated the CFD analyses for bioprosthetic AVR. Before the procedure, the patient also had abnormal right-handed helical flow pattern. The peak velocity and the mean pressure gradient were 5.8 m/s and 89 mmHg, respectively. The highest pressure and WSS were in the great outer curvature. After the procedure, although the blood flow patterns improved, there was residual right-handed helical flow pattern. The peak velocity and the mean pressure gradient were 2.7 m/s and 17 mmHg, respectively. While the pressure and the WSS decreased (from 76 to 40 Pa), the pressure in the great outer curvature still seemed to be high (from 16,253 to 15,724 Pa).

Figure 2 Representative of computational fluid dynamic-generated flow patterns in patient 2 (bioprosthetic valve).

Figure 3 demonstrated the CFD analyses for TAVR. Before the procedure, the patient had abnormal helical flow pattern in the posterior ascending aorta. The peak velocity and the mean pressure gradient were 5.3 m/s and 67 mmHg, respectively. The highest pressure and WSS were in the great outer curvature. After the procedure, there was slight residual right-handed helical flow pattern. The peak velocity and the mean pressure gradient were 2.7 m/s and 13 mmHg, respectively. The pressure and the WSS also decreased (pressure from 19,557 to 15,672 Pa, WSS from 68 to 21 Pa).

Figure 3 Representative of computational fluid dynamic-generated flow patterns in patient 3 (transcatheter heart valve).

Discussion

Currently there are two main theories explaining the mechanism of bicuspid aortopathy: genetics and hemodynamics. In BAV patients with severe aortic stenosis, the intrinsically vulnerable aortic wall is exposed to the aberrant eccentric and spiral flow jets created by the abnormal aortic valve (8). This might partially explain the ascending aortic dilation. In the present study, we observed preoperative abnormal helical flow and asymmetrically elevated pressure and WSS in all patients. Following AVR, blood flow patterns appeared to improve with decrease of pressure and WSS.

Mechanical AVR seemed to have good hemodynamics. This result is supported by several previous studies, which described better hemodynamic or long-term outcome after mechanical AVR compared with bioprosthetic AVR (10,13,14). For example, Bissell et al. (14) found that mechanical AVR showed a significant reduction in rotational flow (from 30.4±16.3 to 7.3±4.1 mm²/ms; P<0.05) and WSS (from 0.47±0.20 to 0.20±0.13 N/m²; P<0.05), whereas these parameters remained similar in the bioprosthetic AVR group. One possible explanation is the bileaflet design of the mechanical valve, which has non-physiological opening and produces two parallel flow jets arising off-center. This may reduce the overall rotational flow and decreased the pressure and the WSS in the ascending aorta.

Bioprosthetic AVR appeared to have remnant helices and relatively high residual pressure and WSS. One hypothesis is that bioprostheses contain a sewing ring that might impede the blood flow. By comparison, transcatheter valves are fixed at the aortic wall. Several previous studies have reported the better hemodynamic performances of TAVR compared with bioprosthetic AVR (15,16). For example, the NOTION trial compared the performance and durability after TAVR or SAVR (bioprosthetic valve) (15). They found more favorable hemodynamic parameters after TAVR, reflected by transprosthetic gradient and effective orifice area (P<0.05). However, these results need further confirmation in the future studies.

To date studies regarding ascending aortic expansion after isolated AVR remains inconclusive. While some studies found continued ascending aortic dilation after SAVR or TAVR in patients with BAV (17-19), others showed that SAVR or TAVR could prevent progressive aortic dilation (20-21). In addition, very few studies have compared the postoperative ascending aortic dilation and adverse aortic events between patients using mechanical and bioprosthetic valves. Based on the results of the present study, one possible explanation might be that blood flow patterns in the ascending aorta differ post AVR. Large studies comparing hemodynamics and ascending aortic dilation rate in mechanical, bioprosthetic, and transcatheter valves would be ideal.

Several limitations should be acknowledged. First, the sample size is small and there is no statistical analysis and comparison. The three individual cases just provide the feasibility of performing CFD analysis in BAV patients undergoing difference type of AVR. Therefore, the results of the present study should be interpreted cautiously. Second, several simplifications and assumptions were made during the CFD analyses. For example, we used CDF with rigid wall assumptions. While FSI offers superior biomechanical fidelity, rigid-wall CFD remains a well-validated, widely used method for comparative hemodynamic analyses (22). This is particularly true when evaluating relative changes in flow patterns (e.g., pre-versus post-operative conditions) rather than absolute quantitative values. Although previous studies showed key parameters like peak WSS may differ by 10–20% between rigid and compliant wall models (23), this does not compromise the comparative insights of our study. Our choice to use a rigid-wall model was driven by the exploratory nature of the present study, as well as the significant computational resources required for FSI simulations across multiple patient-specific geometries. Another simplification is to apply zero pressure for all outlets, which might neglect physiological pressure distributions and downstream impedance. However, previous reports showed that zero pressure for outlets is feasible when the patient-specific pressure measurements are not available (24). Therefore, the present study can be considered as a pivot study to evaluate the feasibility of our methods. Third, the relationship between the postoperative hemodynamics and the ascending aortic dilation is not analyzed. Our previous studies have found that in patients with BAV and ascending aortic dilation who underwent TAVR, the ascending aortic diameter showed a trend toward expansion (25). In the future study, we would focus on the role of different types of valves and their hemodynamic performance in postoperative ascending aortic expansion.

Conclusions

Abnormal aortic flow patterns appeared to improve after AVR in patients with BAV. The type of aortic prostheses might be an influence on the hemodynamics, which requires further studies.

Acknowledgments

We would like to thank Samuel Lv for his help in polishing our paper.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://cdt.amegroups.com/article/view/10.21037/cdt-2025-1-643/rc

Peer Review File: Available at https://cdt.amegroups.com/article/view/10.21037/cdt-2025-1-643/prf

Funding: This work was supported by the Fundamental Research Funds for the Central Universities (No. 3332024024) and Noncommunicable Chronic Diseases-National Science and Technology Major Project (No. 2023ZD0514300).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://cdt.amegroups.com/article/view/10.21037/cdt-2025-1-643/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the institutional review board of Fuwai Hospital (date of review, 24 February 2025; approval No. 2025-2627). Written informed consent was obtained from the patients for the publication of this case report. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Masri A, Svensson LG, Griffin BP, et al. Contemporary natural history of bicuspid aortic valve disease: a systematic review. Heart 2017;103:1323-30. [Crossref] [PubMed]
2. Verma S, Siu SC. Aortic dilatation in patients with bicuspid aortic valve. N Engl J Med 2014;370:1920-9. [Crossref] [PubMed]
3. Guzzardi DG, Verma S, Fedak PW. Bicuspid aortic valve aortopathy: mechanistic and clinical insights from recent studies. Curr Opin Cardiol 2017;32:111-6. [Crossref] [PubMed]
4. Otto CM, Nishimura RA, Bonow RO, et al. 2020 ACC/AHA Guideline for the Management of Patients With Valvular Heart Disease: Executive Summary: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation 2021;143:e35-71. [Crossref] [PubMed]
5. Nishimura RA, Otto CM, Bonow RO, et al. 2017 AHA/ACC Focused Update of the 2014 AHA/ACC Guideline for the Management of Patients With Valvular Heart Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Circulation 2017;135:e1159-95. [Crossref] [PubMed]
6. Cilla M, Casales M, Peña E, et al. A parametric model for studying the aorta hemodynamics by means of the computational fluid dynamics. J Biomech 2020;103:109691. [Crossref] [PubMed]
7. Morris PD, Narracott A, von Tengg-Kobligk H, et al. Computational fluid dynamics modelling in cardiovascular medicine. Heart 2016;102:18-28. [Crossref] [PubMed]
8. Nordmeyer S, Hellmeier F, Yevtushenko P, et al. Abnormal aortic flow profiles persist after aortic valve replacement in the majority of patients with aortic valve disease: how model-based personalized therapy planning could improve results. A pilot study approach. Eur J Cardiothorac Surg 2020;57:133-41. [Crossref] [PubMed]
9. Marx P, Kowalczyk W, Demircioglu A, et al. The Fluid Dynamical Performance of the Carpentier-Edwards PERIMOUNT Magna Ease Prosthesis. Biomed Res Int 2018;2018:5429594. [Crossref] [PubMed]
10. Botzenhardt F, Hoffmann E, Kemkes BM, et al. Determinants of ascending aortic dimensions after aortic valve replacement with a stented bioprosthesis. J Heart Valve Dis 2007;16:19-26. [PubMed]
11. Liu H, Lan L, Abrigo J, et al. Comparison of Newtonian and Non-newtonian Fluid Models in Blood Flow Simulation in Patients With Intracranial Arterial Stenosis. Front Physiol 2021;12:718540. [Crossref] [PubMed]
12. Steinman DA, Taylor CA. Flow imaging and computing: large artery hemodynamics. Ann Biomed Eng 2005;33:1704-9. [Crossref] [PubMed]
13. Hellmeier F, Nordmeyer S, Yevtushenko P, et al. Hemodynamic Evaluation of a Biological and Mechanical Aortic Valve Prosthesis Using Patient-Specific MRI-Based CFD. Artif Organs 2018;42:49-57. [Crossref] [PubMed]
14. Bissell MM, Loudon M, Hess AT, et al. Differential flow improvements after valve replacements in bicuspid aortic valve disease: a cardiovascular magnetic resonance assessment. J Cardiovasc Magn Reson 2018;20:10. [Crossref] [PubMed]
15. Thyregod HGH, Jørgensen TH, Ihlemann N, et al. Transcatheter or surgical aortic valve implantation: 10-year outcomes of the NOTION trial. Eur Heart J 2024;45:1116-24. [Crossref] [PubMed]
16. Clavel MA, Webb JG, Rodés-Cabau J, et al. Comparison between transcatheter and surgical prosthetic valve implantation in patients with severe aortic stenosis and reduced left ventricular ejection fraction. Circulation 2010;122:1928-36. [Crossref] [PubMed]
17. Yasuda H, Nakatani S, Stugaard M, et al. Failure to prevent progressive dilation of ascending aorta by aortic valve replacement in patients with bicuspid aortic valve: comparison with tricuspid aortic valve. Circulation 2003;108:II291-4. [Crossref] [PubMed]
18. He YX, Fan JQ, Zhu QF, et al. Ascending aortic dilatation rate after transcatheter aortic valve replacement in patients with bicuspid and tricuspid aortic stenosis: A multidetector computed tomography follow-up study. World J Emerg Med 2019;10:197-204. [Crossref] [PubMed]
19. Chiariello GA, Di Mauro M, Pasquini A, et al. Progression of the ascending aorta diameter after surgical or transcatheter bicuspid aortic valve replacement. Interdiscip Cardiovasc Thorac Surg 2024;38:ivae100. [Crossref] [PubMed]
20. Abdulkareem N, Soppa G, Jones S, et al. Dilatation of the remaining aorta after aortic valve or aortic root replacement in patients with bicuspid aortic valve: a 5-year follow-up. Ann Thorac Surg 2013;96:43-9. [Crossref] [PubMed]
21. Lv WY, Zhao ZG, Li SJ, et al. Progression of the Ascending Aortic Diameter After Transcatheter Aortic Valve Implantation: Based on Computed Tomography Images. J Invasive Cardiol 2019;31:E234-41. [Crossref] [PubMed]
22. Mendez V, Di Giuseppe M, Pasta S. Comparison of hemodynamic and structural indices of ascending thoracic aortic aneurysm as predicted by 2-way FSI, CFD rigid wall simulation and patient-specific displacement-based FEA. Comput Biol Med 2018;100:221-9. [Crossref] [PubMed]
23. Zhu Y, Mirsadraee S, Rosendahl U, et al. Fluid-Structure Interaction Simulations of Repaired Type A Aortic Dissection: a Comprehensive Comparison With Rigid Wall Models. Front Physiol 2022;13:913457. [Crossref] [PubMed]
24. Taylor CA, Figueroa CA. Patient-specific modeling of cardiovascular mechanics. Annu Rev Biomed Eng 2009;11:109-34. [Crossref] [PubMed]
25. An K, Zhang F, Ouyang W, et al. Influence of ascending aortic dilation in patients undergoing transcatheter aortic valve replacement: A multicenter, retrospective study. JTCVS Structural and Endovascular 2025;6:100055. [Crossref]