Use of patient-specific computational models for optimization of aortic insufficiency after implantation of left ventricular assist device

Abstract

Objective: Aortic incompetence (AI) is observed to be accelerated in the continuous-flow left ventricular assist device (LVAD) population and is related to increased mortality. Using computational fluid dynamics (CFD), we investigated the hemodynamic conditions related to the orientation of the LVAD outflow in these patients.

Method: We identified 10 patients with new aortic regurgitation, and 20 who did not, after LVAD implantation between 2009 and 2018. Three-dimensional models of patients' aortas were created from their computed tomography scans. The geometry of the LVAD outflow graft in relation to the aorta was quantified using azimuth angles (AA), polar angles (PAs), and distance from aortic root. The models were used to run CFD simulations, which calculated the pressures and wall shear stress (rWSS) exerted on the aortic root.

Results: The AA and PA were found to be similar. However, for combinations of high values of AA and low values of PA, there were no patients with AI. The distance from aortic root to the outflow graft was also smaller in patients who developed AI (3.39 ± 0.7 vs 4.07 ± 0.77 cm, P = .04). There was no significant difference in aortic root pressures in the 2 groups. The rWSS was greater in AI patients (4.60 ± 5.70 vs 2.37 ± 1.20 dyne/cm², P < .001). Qualitatively, we observed a trend of greater perturbations, regions of high rWSS, and flow eddies in the AI group.

Conclusions: Using CFD simulations, we demonstrated that patients who developed de novo AI have greater rWSS at the aortic root, and their outflow grafts were placed closer to the aortic roots than those patients without de novo AI.

Keywords: SimVascular; aortic incompetence; computational fluid dynamics; heart failure; left ventricular assist device.

Figure 1

SimVascular pipeline to generate 3D CFD simulations. CT images were used to create pathlines. 3D models were generated using manually defined vessel boundaries created at horizontal cross-sections. Simulations of the models discretized into an unstructured mesh were ran on the Sherlock cluster and post-processed in ParaView.

Figure 2:

A. Two panels showing the azimuth or ‘horizontal’ angle on a 3D reconstructed aorta, along with the plane that intersects the ascending and descending aorta. B. Panel showing the polar angle or ‘vertical inclination’ on the same geometry. C. A schematic diagram showing the relationship between the polar and azimuth angles.

Figure 3:

A plot depicting the 3-dimensional conformation of the outflow graft in relation to the aorta: Polar angle is on the x-axis, and Azimuth angle on the y-axis. For the 3-dimensional configuration of low Polar angles coupled with a high Azimuth angle, almost none of the patients had AI.

Figure 4:

Box plots showing the differences in distance from the aortic root to the entry point of the LVAD outflow graft (left). Measured pressures were found to not be significantly different between the two groups.

Figure 5:

Post-processed Wall shear stress renders of a patient with A: AI and B: No AI. Red color mapped regions indicate high values while blue indicates low values of velocity and WSS.

Figure 6:

Computed tomography images were used to create 3D models for computation fluid dynamics simulations in 30 patients who underwent LVAD placement. Certain geometric positions of the LVAD outflow grafts predict the risk of development of Ai in LVAD patients.