Coronary flow and physiology beyond the stenosis

Blood flow in the coronary circulation is normally well regulated and able to meet even strenuous demand. The presence of an epicardial stenosis poses multiple challenges for safeguarding coronary blood flow and myocardial perfusion, which is further exacerbated by the concurrent presence of microvascular disease. The ability to adjust flow adequately during physiological stress is compromised and myocardial perfusion is redistributed away from the subendocardium. Recent technological advancements have enabled the invasive quantification of epicardial and microvascular pathologies in the catheterization laboratory by intracoronary hemodynamic measurements. The advantages and disadvantages of the various approaches are presented on the basis of the underlying physiological models. Among these, combined measurements of pressure and flow velocity yield more comprehensive information on the functional effect of a stenosis and the status of the downstream microvascular compartment. This article will give a brief overview of coronary physiology, with a focus on the role of microvascular resistance in diagnosis and treatment evaluation.