In-vivo assessment of the morphology and hemodynamic functions of the BioValsalva™ composite valve-conduit graft using cardiac magnetic resonance imaging and computational modelling technology

Abstract

Background: The evaluation of any new cardiac valvular prosthesis should go beyond the classical morbidity and mortality rates and involve hemodynamic assessment. As a proof of concept, the objective of this study was to characterise for the first time the hemodynamics and the blood flow profiles at the aortic root in patients implanted with BioValsalva™ composite valve-conduit using comprehensive MRI and computer technologies.

Methods: Four male patients implanted with BioValsalva™ and 2 age-matched normal controls (NC) underwent cardiac magnetic resonance imaging (MRI). Phase-contrast imaging with velocity-mapping in 3 orthogonal directions was performed at the level of the aortic root and descending thoracic aorta. Computational fluid dynamic (CFD) simulations were performed for all the subjects with patient-specific flow information derived from phase-contrast MR data.

Results: The maximum and mean flow rates throughout the cardiac cycle at the aortic root level were very comparable between NC and BioValsalva™ patients (541 ± 199 vs. 567 ± 75 ml/s) and (95 ± 46 vs. 96 ± 10 ml/s), respectively. The maximum velocity (cm/s) was higher in patients (314 ± 49 vs. 223 ± 20; P = 0.06) due to relatively smaller effective orifice area (EOA), 2.99 ± 0.47 vs. 4.40 ± 0.24 cm2 (P = 0.06), however, the BioValsalva™ EOA was comparable to other reported prosthesis. The cross-sectional area and maximum diameter at the root were comparable between the two groups. BioValsalva™ conduit was stiffer than the native aortic wall, compliance (mm2 • mmHg(-1) • 10(-3)) values were (12.6 ± 4.2 vs 25.3 ± 0.4.; P = 0.06). The maximum time-averaged wall shear stress (Pa), at the ascending aorta was equivalent between the two groups, 17.17 ± 2.7 (NC) vs. 17.33 ± 4.7 (BioValsalva™ ). Flow streamlines at the root and ascending aorta were also similar between the two groups apart from a degree of helical flow that occurs at the outer curvature at the angle developed near the suture line.

Conclusions: BioValsalva™ composite valve-conduit prosthesis is potentially comparable to native aortic root in structural design and in many hemodynamic parameters, although it is stiffer. Surgeons should pay more attention to the surgical technique to maximise the reestablishment of normal smooth aortic curvature geometry to prevent unfavourable flow characteristics.

Figure 1

Three-dimensional geometries of the aorta for all subjects. (a) Normal control group and (b) BioValsalva™ patients group. The normal smooth curvature of the aorta is lost in BioValsalva^TM patients.

Figure 2

Volumetric flow rate waveforms and spatiotemporal velocity profile. a) Shows the similarity in volumetric flow rate waveforms at aortic root between the normal controls and BioValsalva™ patients. b) The spatiotemporal through-plane velocity profile at aortic root of subject Normal #1 (top) and Patient #1 (bottom), the velocity profile of the BioValsalva™ was steeper and with higher peak than the normal.

Figure 3

The in-plane and the through-plane velocities at aortic root. The in-plane velocity projected on the cross section area of aortic root (vectors) and the through-plane velocity (color contours) are visualized for subject Normal #1 (top) and Patient #1 (bottom). Although the in-plane flow is organized in the orifice area in both subjects, the BioValsalva™ patient is more likely to have swirl near the edge of orifice area.

Figure 4

The effective orifice area (EOA). Colour-coded velocity map showing the EOA at peak flow rate above the valves (broken lines) for all subjects, (a) Normal control group and (b) BioValsalva™ patients group. The shapes of the EOA in BioValsalva™ are less regular and smaller.

Figure 5

The time-averaged Wall Shear Stress (TAWSS) for subject Normal #1 and Patient #1. The maximum TAWSS values were comparable between the two groups, but the spatial distribution of areas with high wall shear stress was different.

Figure 6

Flow streamlines for subject Normal #1 and Patient #1. The flow at the outer curvature of the ascending aorta was more uniform and streamlined in normal aorta in comparison to the BioValsalva™ patient.