The Effect of Graft Caliber Upon Wall Shear Within in Vivo Distal Vascular Anastomoses

Abstract

Wall shear has been widely implicated as a contributing factor in the development of intimal hyperplasia in the anastomoses of chronic arterial bypass grafts. Earlier studies have been restricted to either: (1) in vitro or computer simulation models detailing the complex hemodynamics within an anastomosis without corresponding biological responses, or (2) in vivo models that document biological effects with only approximate wall shear information. Recently, a specially designed pulse ultrasonic Doppler wall shear rate (PUDWSR) measuring device has made it possible to obtain three near-wall velocity measurements nonintrusively within 1.05 mm of the vessel luminal surface from which wall shear rates (WSRs) were derived. It was the purpose of this study to evaluate the effect of graft caliber, a surgically controllable variable, upon local hemodynamics, which, in turn, play an important role in the eventual development of anastomotic hyperplasia. Tapered (4-7 mm I.D.) 6-cm-long grafts were implanted bilaterally in an end-to-side fashion with 30 deg proximal and distal anastomoses to bypass occluded common carotid arteries of 16 canines. The bypass grafts were randomly paired in contralateral vessels and placed such that the graft-to-artery diameter ratio, DR, at the distal anastomosis was either 1.0 or 1.5. For all grafts, the average Re was 432 +/- 112 and the average Womersley parameter, alpha, was 3.59 +/- 0.39 based on artery diameter. There was a sharp skewing of flow toward the artery floor with the development of a stagnation point whose position varied with time (up to two artery diameters) and DR (generally more downstream for DR = 1.0). Mean WSRs along the artery floor for DR = 1.0 and 1.5 were found to range sharply from moderate to high retrograde values (589 s-1 and 1558 s-1, respectively) upstream to high antegrade values (2704 s-1 and 2302 s-1, respectively) immediately downstream of the stagnation point. Although there were no overall differences in mean and peak WSRs between groups, there were significant differences (p < 0.05) in oscillatory WSRs as well as in the absolute normalized mean and peak WSRs between groups. There were also significant differences (p < 0.05) in mean and peak WSRs with respect to axial position along the artery floor for both DR cases. In conclusion, WSR varies widely (1558 s-1 retrograde to 2704 s-1 antegrade) within end-to-side distal graft anastomoses, particularly along the artery floor, and may play a role in the development of intimal hyperplasia through local alteration of mass transport and mechano-signal transduction within the endothelium.

Distal end side-to-side anastomoses of sequential vein graft to small target coronary arteries improve intraoperative graft flow

“…Graft-host diameter ratio can influence graft hemodynamics at end-to-side anastomoses substantially [2-4]. In a computational simulation model of CABG, Qiao et al reported that large graft-host diameter ratio (1.46) produces better hemodynamics than equal or small (0.8) ratio when the diameter of a target vessel is assumed to be 2.5 mm [5].…”

“…Spivack et al reported that the mean diameter of the great saphenous vein (GSV), which is commonly used for sequential CABG, is between 2.3 mm to 4.4 mm [1]; while the average diameter of small target coronary arteries of Chinese patients is usually 1 mm. Graft-host diameter ratio has been shown to influence distal anastomotic hemodynamics and consequently graft patency [2-4]. Although large graft-host diameter ratio has been shown to have better hemodynamic performance than smaller ones under end-to-side anastomoses [5], the oversize diameter ratio between the GSV and small target coronary arteries might induce adverse hemodynamics condition and compromise graft patency.…”

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

“…Generalized 49 and system specific 20,38 observations of IH localization have been shown to correlate with regions of low wall shear stress (WSS) and high oscillatory shear index (OSI) 3,21,22,38,42 as well as with variations in the WSSfield as determined by the WSS-gradient (WSSG) 25,51 and WSS-angle-gradient (WSSAG). 24 Intimal hyperplasia along the suture-line is widely associated with surgical injury, suture technique, compliance mismatch, and intramural strain.…”

Mechanical analysis of end‐to‐end silk‐sutured anastomosis for robot‐assisted surgery

“…Unfortunately, quite often the quality of the vessel anastomosis is not very satisfactory and may decrease significantly over time. Consequently, many researchers seek approaches to ensure the quality of anastomosis by adjusting the appropriate values of process variables (22)(23)(24)(25)(26)(27). However, most of them focus on the wall shear stress distribution that may induce intimal hyperplasia and thrombosis, hence ultimate failure in anastomosis.…”