Abstract
Introduction:
Aortic valve insufficiency (AI) and atherosclerotic emboli have been described in patients with continuous flow left ventricular assist devices (cf-LVAD). The mechanisms are unknown. We established a new method for analysis of flow dynamics and aortic wall shear stress (WSS) using computational fluid dynamics (CFD) of computer tomography (CT) studies. Aim of our study was to examine the role of blood flow and WSS in pathologic aortic processes in patients with LVAD.
Method:
5 patients with cf-LVAD and 2 patients with pulsatile flow (p) LVAD had a CT 9.9 ± 9.2 months after device implantation. Transient CFD simulations with turbulent k-å model performing LVAD flow waveforms for pulsatile cases were conducted (time step: 5 msec, 3 cardiac cycles). Flow pattern, dynamic pressure and wall shear stress (WSS) of the aorta were quantified.
Result:
In cf- LVAD patients, outflow graft position (lateral or anterior) determined hemodynamics in the aorta. Figure 1 representatively depicts the results: Panels A to D refer to continuous flow. In panel A and B lateral outflow graft positioning is associated with a high WSS caused by flow impingement (arrow) indicating contra-lateral focal high pressure (3 – 5 x higher than in descending aorta) and vertical vortices in the aortic root while no focal pressure and horizontal vortices dominated in panel C and D (anterior outflow graft positioning). For comparison, p-LVAD (panel E), the magnitude of retrograde flow in the ascending aorta varied by one order of magnitude during systole and diastole and WSS of the opposite wall to LVAD outflow varied from 3 – 4 Pa (diastole) to 31 Pa (systole).
Conclusion:
CFD of CT-scans enables analysis of pathologic aortic processes. Continuous vertical vortex formation in the aortic root may contribute to aortic insufficiency in patients with cf-LVAD support. Outflow graft position determines focal pressure on the aortic wall and shear off of aortic plaques.
Fig. 1:
CFD