Comparative study of different left ventricular assist device outflow graft placement on patient haemodynamics

Objectives: To evaluate through a computational fluid dynamics (CFD) model, the fluid dynamics of the outflow graft of a continuous flow left ventricular assist device (LVAD) placed at different heights along the ascending aorta, to determine the insertion site with the best haemodynamic profile. Methods: In the CFD model, the outflow graft was inserted in the ascending part of a patient-specific aorta (attained from angio CT) at four different heights above the sinotubular junction: 1 cm (case 1), 2 cm (case 2), 3 cm (case 3) and 4 cm (case 4), with an insertion angle of 20 degrees. The simula- tion was carried out using COMSOL 4.3a (COMSOL Inc, Stockholm, Sweden). Results: In all cases, the ascending aorta presented high vorticity but with more flow stagnation the higher the outflow graft was. In cases 1-2, the epiaor- tic vessels had steady velocity, while in cases 3-4 the flow was turbulent. The time averaged wall shear stress (TAWSS) distribution showed maximum values: in the ascending aorta, cases 1-2 - 6.7 Pa and 6.2 Pa, respectively; in the infer- ior curvature of the arch, case 3 - 5.6 Pa; between the epiaortic vessels, case 4 - 13.8 Pa. The shear stress over the closed aortic valve was 2 Pa in case 1, 1 Paincase2,0.5Paincase3,<0.2incase4. Conclusions: The computational model suggested that the placement of the outflow graft between 2 and 3 cm above the ST junction gives the most favour- able haemodynamic profile.