Annular dilatation and loss of sino-tubular junction in aneurysmatic aorta: implications on leaflet quality at the time of surgery. A finite element study

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.

[Effect of sinus diameter on the opening and closing performance of aortic valve under the expansion of aortic root]

This study aims to explore the effect of aortic sinus diameter on aortic valve opening and closing performance in the case of no obvious disease of aortic valve and annulus and continuous dilation of aortic root. A total of 25 three-dimensional aortic root models with different aortic sinus and root diameters were constructed according to the size of clinical surgical guidance. The valve sinus diameter DS is set to 32, 36, 40, 44 and 48 mm, respectively, and the aortic root diameter DA is set to 26, 27, 28, 29 and 30 mm, respectively. Through the structural mechanics calculation with the finite element software, the maximum stress, valve orifice area, contact force and other parameters of the model are analyzed to evaluate the valve opening and closing performance under the dilated state. The study found that aortic valve stenosis occurs when the DS = 32 mm, DA = 26, 27 mm and DS = 36 mm, DA = 26 mm. Aortic regurgitation occurs when the DS = 32, 36 and 40 mm, DA = 30 mm and DS = 44, 48 mm, DA = 29, 30 mm. The other 15 models had normal valve movement. The results showed that the size of the aortic sinus affected the opening and closing performance of the aortic valve. The smaller sinus diameter adapted with the larger root diameter and the larger sinus diameter adapted with the smaller root diameter. When the sinus diameter is 40 mm, the mechanical performance of the valve are good and it can well adapt with the relatively large range of aortic root dilation.

Gender Related Association between Arterial Stiffness and Aortic Root Geometry

BACKGROUND

The gender-related change in aortic morphology by arterial stiffness has not been well studied. This study was performed to investigate the association between brachial-ankle pulse wave velocity (baPWV) and aortic root size according to gender.

METHODS

A total of 263 consecutive subjects (63.2 ± 10.6 years, 71.1% men) without overt cardiovascular disease who underwent both baPWV measurement and transthoracic echocardiography on the same day were retrospectively analyzed. The diameters of the aortic annulus (AN), sinus of Valsalva (SV), sinotubular junction (STJ), and ascending aorta (AA) were measured using 2-dimensional echocardiography.

RESULTS

The body surface area (BSA)-corrected diameters of AN, SV, STJ, and AA were significantly higher in women than in men. Univariable analyses showed that baPWV was significantly correlated with SV/BSA and STJ/BSA in men, and with SV/BSA, STJ/BSA, and AA/BSA in women (p < 0.05 for each). In men, however, these associations disappeared in multiple linear regression models after controlling for potential confounders (p > 0.05 for each). In women, the associations of baPWV with diameters of STJ/BSA (β = 0.407, p < 0.001) and AA/BSA (β = 0.391, p = 0.005) remained significant in the same multivariate models. Women-specific correlation between aortic root size and baPWV was also similarly demonstrated in age-matched analyses (n = 61 in each gender).

CONCLUSIONS

Among Korean adult without overt cardiovascular disease, the association between increased arterial stiffness and aortic root dilatation is stronger in women than in men.

[Experimental study of the effects of sinotubular junction taper on artificial bioprosthesis valve in pulsatile flow condition]

The aim of the present experimental study is to determine the effects of sinotubular junction diameter on artificial bioprosthesis valves. An experimental study was performed for aortic root models with different sinotubular junction taper under pulsatile flow condition. The sinotubular junction diameters were modified to create four models with different sinotubular junction tapers with 0, 1, 3 and 5 degrees, respectively, using three dimensional printing techniques. After installing the testing bioprosthesis valve on the aortic root models, we conducted experiments of the pulsatile flow testing with different stroke volume in the pulsatile circulation simulation system. The testing condition was set at the pulse frequency of 70 beats/min and the stroke volume of 2-7 L/min. The status of the valves in 10 continuous pulse cycles was tested and the average results were obtained for each stroke volume. The results of testing showed that the mean transvalvular pressure gradients agreed well with the national standard, and all smaller than 10 mm Hg. The sinotubular junction taper had an influence on regurgitation fraction of the artificial bioprosthesis valve. The smaller sinotubular junction taper showed beneficial effect to decrease the regurgitation fraction. In the case of smaller stroke volume, the smaller sinotubular junction taper was beneficial to increase the effective valve orifice area. In the case of larger stroke volume, the larger sinotubular junction taper was beneficial to increase the effective valve orifice area. This study indicates that a doctor should consider the smaller sinotubular junction taper in the case of smaller stroke volume more. In the case of larger stroke volume, the doctor should consider the larger sinotubular junction taper more.

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.