title: Impact of competitive flow on wall shear stress in coronary surgery: computational fluid dynamics of a LIMA-LAD model.
abstract: OBJECTIVE
  Competitive flow from native coronary vessels is considered a major factor in the failure of coronary bypass grafts. However, the pathophysiological effects are not fully understood. Low and oscillatory wall shear stress (WSS) is known to induce endothelial dysfunction and vascular disease, like atherosclerosis and intimal hyperplasia. The aim was to investigate the impact of competitive flow on WSS in mammary artery bypass grafts.
  
  
  RESULTS
  Using computational fluid dynamics, WSS was calculated in a left internal mammary artery (LIMA) graft to the left anterior descending artery in a three-dimensional in vivo porcine coronary artery bypass graft model. The following conditions were investigated: high competitive flow (non-significant coronary lesion), partial competitive flow (significant coronary lesion), and no competitive flow (totally occluded coronary vessel). Time-averaged WSS of LIMA at high, partial, and no competitive flow were 0.3-0.6, 0.6-3.0, and 0.9-3.0 Pa, respectively. Further, oscillatory WSS quantified as the oscillatory shear index (OSI) ranged from (maximum OSI = 0.5 equals zero net WSS) 0.15 to 0.35, <0.05, and <0.05, respectively. Thus, high competitive flow resulted in substantial oscillatory and low WSS. Moderate competitive flow resulted in WSS and OSI similar to the no competitive flow condition.
  
  
  CONCLUSIONS
  Graft flow is highly dependent on the degree of competitive flow. High competitive flow was found to produce unfavourable WSS consistent with endothelial dysfunction and subsequent graft narrowing and failure. Partial competitive flow, however, may be better tolerated as it was found to be similar to the ideal condition of no competitive flow.
authors.affiliation: Department of Circulation and Medical Imaging, The Norwegian University of Science and Technology, N-7489 Trondheim, Norway. haavardnordgaard@gmail.com
authors.forename: Håvard
authors.initials: H
authors.lastname: Nordgaard
authors.forename: Abigail
authors.initials: A
authors.lastname: Swillens
authors.forename: Dag
authors.initials: D
authors.lastname: Nordhaug
authors.forename: Idar
authors.initials: I
authors.lastname: Kirkeby-Garstad
authors.forename: Denis
authors.initials: D
authors.lastname: Van Loo
authors.forename: Nicola
authors.initials: N
authors.lastname: Vitale
authors.forename: Patrick
authors.initials: P
authors.lastname: Segers
authors.forename: Rune
authors.initials: R
authors.lastname: Haaverstad
authors.forename: Lasse
authors.initials: L
authors.lastname: Lovstakken
mesh_terms: D000714:Anastomosis, Surgical; D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology; D001026:Coronary Artery Bypass; D003331:Coronary Vessels / Q000502:physiology* / Q000601:surgery; D004730:Endothelium, Vascular / Q000503:physiopathology; D057446:Hydrodynamics; D008323:Mammary Arteries / Q000502:physiology* / Q000637:transplantation; D023421:Models, Animal; D008955:Models, Cardiovascular; D012039:Regional Blood Flow / Q000502:physiology*; D033081:Shear Strength; D013314:Stress, Mechanical; D013552:Swine