Numerical Simulation of Wall Shear Stress and Particle-Based Hemodynamic Parameters in Pre-Cuffed and Streamlined End-to-Side Anastomoses

Abstract

A number of research studies have related multiple hemodynamic parameters to the formation of distal anastomotic intimal hyperplasia (IH) at the sub-cellular, cellular, and tissue levels. Focusing on mitigating WSS-based parameters alone, several studies have suggested geometrically modified end-to-side anastomoses with the intent of improving synthetic graft patency rates. However, recent clinical trials of commercially available versions of these grafts indicate persistently high rates of failure. Furthermore, recent evidence suggests that platelet-wall interactions may play a significant role in the formation of IH, which is not captured by WSS-based parameters alone. In this study, numerical simulations have been conducted to assess the potential for IH formation in conventional and geometrically modified anastomoses based on both wall shear stress (WSS) conditions and platelet-wall interactions. Sites of significant particle-wall interactions, including elevated concentrations and stasis, were identified by a near-wall residence time model, which includes factors for platelet activation and surface reactivity. Conventional, pre-cuffed, and streamlined distal end-to-side anastomoses were considered with proximal and distal arterial outflow. It was found that a pre-cuffed anastomosis, similar to the Distaflo configuration, does not offer a hemodynamic advantage over the conventional design considered with respect to the magnitude of the WSS field and the potential for platelet interactions with the vessel surface. Streamlined configurations largely consistent with venous confluences resulted in an advantageous reduction of wall shear stress gradient values; however, particle-wall interactions remained significant throughout the anastomosis. Results of this study are not intended to be directly extrapolated to surgical recommendations. However, these results highlight the difficulty associated with designing an end-to-side distal anastomosis with two-way outflow that is capable of simultaneously reducing multiple hemodynamic parameters. Further testing will be necessary to determine if the observed elevated particle-wall interactions in a pre-cuffed anastomosis provide the stimulus responsible for the reported high failure rates of these grafts.

Hemodynamic Comparison of Differing Anastomotic Geometries Using Magnetic Resonance Velocimetry

“…Longest and Kleinstreuer performed a computational study with a model for biological stimulation of hyperplasia [22]. The model was based on near wall residence time of blood, platelet activation, and surface reactivity, and was able to predict hyperplasia formation in agreement with in vivo observations.…”

Coronary artery bypass grafting hemodynamics and anastomosis design: a biomedical engineering review

“…A streamlined anastomotic configuration in which the distal outlet segment (DOS) is aligned with the graft has been developed by Longest et al [159]. This configuration, shown in Figure 17, resulted in an advantageous reduction of the peak normalized WSSG values in the vicinity of the toe (to 1.7 from 11.8 in a conventional ETS model).…”

Full-hexahedral structured meshing for image-based computational vascular modeling

“…With the segmentation process the geometry of the vascular segments of interest is extracted from the medical image and usually stored as a set of triangles in STL (stereolithography) format [6]. Owing to the geometrical complexity of the patient-specific domain defined by the STL surface, automatic meshing schemes using tetrahedral elements have been widely preferred for image-based analysis, both in Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) applications, while structured hexahedral meshes have been rarely adopted or limited to simple geometries [7][8][9][10][11].…”