Fluid-structure interaction simulation of aortic valve closure with various sinotubular junction and sinus diameters

Numerical simulation of fluid-structure interaction analysis for the performance of leaflet reimplantation with different types of artificial graft

BACKGROUND AND OBJECTIVE

In clinical practice, valve-sparing aortic root replacement surgery primarily addresses left ventricular dysfunction in patients due to severe aortic regurgitation, but there is controversy regarding the choice of surgical technique. In order to investigate which type of valve-sparing aortic root replacement surgeries can achieve better blood flow conditions, this study examines the impact of changes in the geometric morphology of the aortic root on the hemodynamic environment through numerical simulation.

METHODS

An idealized model of the aortic root was established based on data obtained from clinical measurements, including using the model of the aortic root without significant lesions as the control group (Model C), while using surgical models of leaflet reimplantation with tubular graft (Model T), leaflet reimplantation with Valsalva graft (Model V), and the Florida sleeve procedure (Model F) as the experimental groups. Fluid-structure interaction numerical simulations were conducted to assess the differences in blood flow between the three surgical techniques.

RESULTS

Compared to the control group, all the three experimental groups showed no abnormal blood flow patterns in the aortic root. Additionally, the distribution of high-velocity blood flow was similar to that of the control group. Due to the changes in geometric shape after surgery, the impact locations of blood on the vessel wall varied, leading to different degrees of wall shear stress concentration at the sinus-conduit junction and the aortic valve ring in the three surgical models. During the peak systolic phase, the maximum opening area of the leaflets in the three surgical models (T, V, and F) differs from that of the control model, with the disparity in aortic valve leaflet opening area being 6.42 %, 9.17 %, and 8.63 %, respectively. When comparing the leaflet closure states, it was found that the closure velocity in Model V was close to that of Model C.

CONCLUSIONS

The changes in the geometry of the aortic sinus affect the hemodynamics within the aorta, and leaflet reimplantation with Valsalva graft and Florida sleeve procedures are more stable during blood flow impacts.

Effect of Sinotubular Junction Size on TAVR Leaflet Thrombosis: A Fluid-Structure Interaction Analysis

TAVR has emerged as a standard approach for treating severe aortic stenosis patients. However, it is associated with several clinical complications, including subclinical leaflet thrombosis characterized by Hypoattenuated Leaflet Thickening (HALT). A rigorous analysis of TAVR device thrombogenicity considering anatomical variations is essential for estimating this risk. Clinicians use the Sinotubular Junction (STJ) diameter for TAVR sizing, but there is a paucity of research on its influence on TAVR devices thrombogenicity. A Medtronic Evolut® TAVR device was deployed in three patient models with varying STJ diameters (26, 30, and 34 mm) to evaluate its impact on post-deployment hemodynamics and thrombogenicity, employing a novel computational framework combining prosthesis deployment and fluid-structure interaction analysis. The 30 mm STJ patient case exhibited the best hemodynamic performance: 5.94 mmHg mean transvalvular pressure gradient (TPG), 2.64 cm2 mean geometric orifice area (GOA), and the lowest mean residence time (TR)-indicating a reduced thrombogenic risk; 26 mm STJ exhibited a 10 % reduction in GOA and a 35% increase in mean TPG compared to the 30 mm STJ; 34 mm STJ depicted hemodynamics comparable to the 30 mm STJ, but with a 6% increase in TR and elevated platelet stress accumulation. A smaller STJ size impairs adequate expansion of the TAVR stent, which may lead to suboptimal hemodynamic performance. Conversely, a larger STJ size marginally enhances the hemodynamic performance but increases the risk of TAVR leaflet thrombosis. Such analysis can aid pre-procedural planning and minimize the risk of TAVR leaflet thrombosis.

Assessment of valve implantation in the descending aorta as an alternative for aortic regurgitation patients not treatable with conventional procedures

BACKGROUND

Aortic Regurgitation (AR) produces the entrance of an abnormal amount of blood in the left ventricle. This disease is responsible for high morbidity and mortality worldwide and may be caused by an aortic valve dysfunction. Surgical and transcatheter aortic valve replacement (TAVR) are the current options for treating AR. They have replaced older procedures such as Hufnagel's one. However, some physicians have reconsidered this procedure as a less aggressive alternative for patients not eligible for surgical or TAVR. Although Hufnagel suggested a 75% regurgitation reduction when a valve is placed in the descending aorta, a quantification of this value has not been reported.

METHODS

In this paper, CFD/FSI numerical simulation is conducted on an idealized geometry. We quantify the effect of placing a bileaflet mechanical heart valve in the descending aorta on a moderate-severe AR case. A three-element Windkessel model is employed to prescribe pressure outlet boundary conditions. We calculate the resulting flow rates and pressures at the aorta and first-generation vessels. Moreover, we evaluate several indices to assess the improvement due to the valve introduction.

RESULTS AND CONCLUSIONS

Regurgitation fraction (RF) is reduced from 37.5% (without valve) to 18.0% (with valve) in a single cardiac cycle. This reduction clearly shows the remarkable efficacy of the rescued technique. It will further ameliorate the left ventricle function in the long-term. Moreover, the calculations show that the implantation in that location introduces fewer incompatibilities' risks than a conventional one. The proposed methodology can be extended to any particular conditions (pressure waveforms/geometry) and is designed to assess usual clinical parameters employed by physicians.

A computational analysis of potential aortic dilation induced by the hemodynamic effects of bicuspid aortic valve phenotypes

BACKGROUND AND OBJECTIVES

The bicuspid aortic valve (BAV) is a major risk factor for the progression of aortic dilation (AD) because of the induced abnormal blood flow environment in aorta. The differences in the development of AD induced by BAV phenotypes remains unclear. Therefore, the objective of this study was to assess the potential locations of AD induced by different phenotypes of BAV. The different effects of opening orifice area and leaflet orientation on ascending aortic hemodynamics in Type-1 BAV was investigated by means of numerical simulation.

METHODS

Finite element dynamic analysis was performed on tricuspid aortic valve (TAV) and BAV models to simulate the motion of the leaflets and obtain the geometrical characteristics of AV at peak systole as a reference, which were used for aortic models. Then, four sets of aortic fluid models were designed according to the leaflet fusion types [TAV; BAV (left-right-coronary cusp fusion, LR; right-non-coronary cusp fusion, RN; left-non-coronary cusp fusion, LN)], and the computational fluid dynamics method was applied to compare the hemodynamic differences within the aorta at peak systole.

RESULTS

The maximum opening area of BAV was significantly reduced, resulting in alterations in aortic hemodynamics compared with TAV. The velocity streamlines were essentially parallel to the aortic wall in TAV. The average pressure and wall shear stress in aorta tend to be stable. In contrary, the eccentricity of BAV orifice jet resulted in high-velocity flow directed toward the ascending aorta (AA) wall and aortic arch for LR and LN; RN features an asymmetrical velocity distribution toward the outer bend of the middle AA, and eccentric flow tends to impact the distal AA. As the flow angle is associated with distinct flow impingement locations, different degrees of WSS and pressure concentration occur along the aortic wall from the AA to the aortic arch in three BAV types.

CONCLUSIONS

The BAV morphotype affects the aortic hemodynamics, and the abnormal blood flow associated with BAV may play a role in AD. The different BAV phenotypes determine the direction of blood flow jet and change the expression of dilation. LR is likely to cause dilation of the tubular AA; RN results in dilation of the middle AA to proximal aortic arch; and LN causes an increased incidence of the tubular AA and the proximal aortic arch.

Effect of Valve Height on the Opening and Closing Performance of the Aortic Valve Under Aortic Root Dilatation

Patients with aortic valve disease can suffer from valve insufficiency after valve repair surgery due to aortic root dilatation. The paper investigates the effect of valve height (Hv) on the aortic valve opening and closing in order to select the appropriate range of Hv for smoother blood flow through the aortic valve and valve closure completely in the case of continuous aortic root dilatation. A total of 20 parameterized three-dimensional models of the aortic root were constructed following clinical surgical guidance. Aortic annulus diameter (DAA) was separately set to 26, 27, 28, 29, and 30 mm to simulate aortic root dilatation. H_V value was separately set to 13.5, 14, 14.5, and 15 mm to simulate aortic valve alterations in surgery. Time-varying pressure loads were applied to the valve, vessel wall of the ascending aorta, and left ventricle. Then, finite element analysis software was employed to simulate the movement and mechanics of the aortic root. The feasible design range of the valve size was evaluated using maximum stress, geometric orifice area (GOA), and leaflet contact force. The results show that the valve was incompletely closed when H_V was 13.5 mm and D_AA was 29 or 30 mm. The GOA of the valve was small when H_V was 15 mm and D_AA was 26 or 27 mm. The corresponding values of the other models were within the normal range. Compared with the model with an H_V of 14 mm, the model with an H_V of 14.5 mm could effectively reduce maximum stress and had relatively larger GOA and less change in contact force. As a result, valve height affects the performance of aortic valve opening and closing. Smaller H_V is adapted to smaller D_AA and vice versa. When H_V is 14.5 mm, the valve is well adapted to the dilatation of the aortic root to enhance repair durability. Therefore, more attention should be paid to H_V in surgical planning.

Early and mid-term follow-up of patients receiving arterial switch operation: a single-center experience

Background

The arterial switch operation (ASO) has become the preferred method for surgical correction of transposition of the great arteries (TGA) and Taussig-Bing anomaly. This study was aimed to analysis the early and mid-term results of patients receiving ASO for TGA and Taussig-Bing anomaly in our institute.

Methods

A single-institution retrospective study was conducted to assess cardiovascular outcomes after ASO between January 2007 and December 2013. A total of 119 consecutive patients were included in this study. The median age at operation was 30 days (range, 1 day-8 years), the median weight was 3.8 kg (range, 2.0-23.0 kg). The ventricular septum was intact in 59 (49.6%) patients, 43 (36.1%) had ventricular septal defect, and 17 (14.3%) had a Taussig-Bing anomaly. We followed up patients with echocardiography. Special attention had been paid to the neo-aortic regurgitation and pulmonary stenosis.

Results

In hospital deaths occurred in 10 (8.4%) patients. The most cause of death was low cardiac output due to deconditioning of the left ventricle and myocardial infarction. Echocardiographic data after ASO were collected in 93 (85.3%) patients at a mean duration of 60.7±20.2 months. Among them, 4 (4.3%) patients had moderate to severe neo-aortic regurgitation, 1 (1.1%) patient had moderate tricuspid regurgitation, 4 (4.3%) patients had moderate pulmonary regurgitation; 1 (1.1%) patients had moderate pulmonary stenosis and no patients had severe stenosis. Only two patients required a surgical reintervention.

Conclusions

The early mortality rate has decreased and the most cause of death was low cardiac output. The outcomes of the ASO using our reconstruction and reimplantation techniques were excellent and the reoperation rate was very low in the early and mid-term follow-up.

Numerical simulation of closure performance for neo-aortic valve for arterial switch operation

Background

Modeling neo-aortic valve for arterial switch surgical planning to simulate the neo-aortic valve closure performance.

Methods

We created five geometrical models of neo-aortic valve, namely model A, model B, model C, model D and model E with different size of sinotubular junction or sinus. The nodes at the ends of aorta and left ventricle duct fixed all the degrees of freedom. Transvalvular pressure of normal diastolic blood pressure of 54 mmHg was applied on the neo-aortic valve cusps. The neo-aortic valve closure performance was investigated by the parameters, such as stress of neo-aortic root, variation of neo-aortic valve ring as well as aortic valve cusps contact force in the cardiac diastole.

Results

The maximum stress of the five neo-aortic valves were 96.29, 98.34, 96.28, 98.26, and 90.60 kPa, respectively. Compared among five neo-aortic valve, aortic valve cusps contact forces were changed by 43.33, −10.00% enlarging or narrowing the sinotubular junction by 20% respectively based on the reference model A. The cusps contact forces were changed by 6.67, −23.33% with sinus diameter varying 1.2 times and 0.8 times respectively.

Conclusions

Comparing with stress of healthy adult subjects, the neo-aortic valve of infant creates lower stress. It is evident that enlarging or narrowing the sinotubular junction within a range of 20% can increase or decrease the maximum stress and aortic valve cusps contact force of neo-aortic valve.