Background: The assessment of remodeling in diffuse atherosclerosis by intravascular ultrasound is hampered by the lack of an appropriate reference segment. Transplant coronary artery disease is an accepted model of diffuse atherosclerosis. Flow-dependent remodeling is regulated by shear stress. Thus, normal levels of shear stress at baseline flow reflect adequate regulation and provide a functional assessment of flow-dependent remodeling.
Methods: The approach was evaluated in 91 patients with transplant coronary artery disease and in 9 non-transplanted controls and 16 control transplant recipients. Quantitative coronary angiography, intracoronary ultrasound and intracoronary velocity studies were performed at baseline and after pharmacologic intervention. Calculated shear stress was compared between these groups and a sub-group with coronary angioplasty at follow-up (8 of 60 patients with control angiography after 23 +/- 8 months). The relation of shear stress to flow, diameter, flow/area ratio and endothelial function was analyzed.
Results: Normal shear stress was found in non-transplanted controls and transplant recipients without coronary artery disease. Patients with coronary angioplasty at follow-up had elevated shear stress and enhanced endothelial dysfunction on the initial investigation. Shear stress was not correlated with flow (r = 0.062, non-significant), but with diameter (r = -0.654), flow/area ratio (r = 0.814) and endothelial dysfunction (r = 0.722).
Conclusion: Calculated local shear stress appears to be useful for the assessment of the adequacy of flow-dependent macrovascular remodeling in diffuse atherosclerosis. Elevated blood flow/area ratio is a potential clinical marker of increased shear stress that reflects inadequate flow-dependent remodeling.