Mathematical Modeling of Patient-Specific Ventricular Assist Device Implantation to Reduce Particulate Embolization Rate to Cerebral Vessels

Abstract

Stroke is the most devastating complication after ventricular assist device (VAD) implantation, with an incidence of 14%-47% despite improvements in device design and anticoagulation. This complication continues to limit the widespread implementation of VAD therapy. Patient-specific computational fluid dynamics (CFD) analysis may elucidate ways to reduce this risk. A patient-specific three-dimensional model of the aortic arch was generated from computed tomography. A 12 mm VAD outflow-graft (VAD-OG) "anastomosed" to the aorta was rendered. CFD was applied to study blood flow patterns. Particle tracks, originating from the VAD, were computed with a Lagrangian phase model and percentage of particles entering the cerebral vessels was calculated. Twelve implantation configurations of the VAD-OG and three particle sizes (2, 4, and 5 mm) were considered. Percentage of particles entering the cerebral vessels ranged from 6% for the descending aorta VAD-OG anastomosis, to 14% for the ascending aorta at 90 deg VAD-OG anastomosis. Values were significantly different among all configurations (X(2) = 3925, p < 0.0001). Shallower and more cephalad anastomoses prevented formation of zones of recirculation in the ascending aorta. In this computational model and within the range of anatomic parameters considered, the percentage of particles entering the cerebral vessels from a VAD-OG is reduced by nearly 60% by optimizing outflow-graft configuration. Ascending aorta recirculation zones, which may be thrombogenic, can also be eliminated. CFD methods coupled with patient-specific anatomy may aid in identifying the optimal location and angle for VAD-OG anastomosis to minimize stroke risk.

Multi-scale pulsatile CFD modeling of thrombus transport in a patient-specific LVAD implantation

“…We hypothesized that an optimal angle and location of anastomosis of the distal VAD-OG along the aortic wall exists that minimizes thromboembolism to the great vessels. Indeed our results indicated stroke incidence variabilities of as much as 50 per cent dependent upon VAD-OG implantation (Osorio et al , 2013; Argueta-Morales et al , 2010; Argueta-Morales et al , 2014). These results prompted further study of this concept incorporating pulsatility.…”

“…The 3D hemodynamics are resolved by solving the Navier–Stokes equations: for the velocity field Vtrue→ using the commercial CFD code StarCCM+. The fluid domain is patient-derived from computed tomography (CT) scans processed using the medical segmentation software Mimics and modified to accommodate the VAD-OG (Taylor and Figueroa, 2009) that is implanted in the intermediate configuration (Figure 7) as referred to in our previous paper (Argueta-Morales et al , 2014). Rigid walls are considered to reduce computational expense and simplify the system.…”

“…We develop a multiscale 0D-3D approach: 0D Windkessel elements are assembled into a lumped parameter model (LPM) of the peripheral vasculature that provides pulsatile boundary conditions (BCs) interactively driving the 3D CFD models of the VAD circulation that is coupled to a Lagrangian particle-tracking scheme for the thrombi (Prather, 2015). In this paper, we hold VAD-OG implantation in the intermediate configuration referred to in Argueta-Morales et al (2014), and we consider three sources of potential thrombus entering the aortic VAD bed emanating from the inlet of the VAD outflow graft, the aortic root and the ventricle itself.…”