Tailoring left ventricular assist device cannula implantation using coupled multi-scale multi-objective optimization

Background: The frequent occurrence of thromboembolic cerebral events continues to limit the widespread implementation of Ventricular Assist Devices (VAD) despite continued advancements in VAD design and anticoagulation treatments. Recent studies point to the optimal positioning of the outflow graft (OG) as a potential mitigator of post implantation thromboembolism. Objective: This study aims to examine the tailoring of the OG implantation orientation with the goal of minimizing the number of thrombi reaching the cerebral vessels by means of a formal shape optimization scheme incorporated into a multi-scale hemodynamics analysis. Methods: A 3-D patient-specific computational fluid dynamics model is loosely coupled in a two-way manner to a 0-D lumped parameter model of the peripheral circulation. A Lagrangian particle-tracking scheme models and tracks thrombi as non-interacting solid spheres. The loose coupling between CFD and LPM is integrated into a geometric shape optimization scheme which aims to optimize an objective function that targets a drop in cerebral embolization, and an overall reduction in particle residence times. Results: The results elucidate the importance of OG anastomosis orientation and placement particularly in the case that studied particle release from the OG, as a fivefold decrease in cerebral embolization was observed between the optimal and non-optimal implantations. Another case considered particle release from the ventricle and aortic root walls, in which optimal implantation was achieved with a shallow insertion angle. Particle release from all three origins was investigated in the third case, demonstrating that the optimal configurations were generally characterized by VAD flow directed along the central lumen of the aortic arch. Because optimal configurations depended on the anatomic origin of the thrombus, it is important to determine, in clinical studies, the most likely sites of thrombus formation in VAD patients.