Coronary pressure-flow relations as basis for the understanding of coronary physiology

Recent technological advancements in the area of intracoronary physiology, as well as non-invasive contrast perfusion imaging, allow to make clinical decisions with respect to percutaneous coronary interventions and to identify microcirculatory coronary pathophysiology. The basic characteristics of coronary hemodynamics, as described by pressure–flow relations in the normal and diseased heart, need to be understood for a proper interpretation of these physiological measurements. Especially the hyperemic coronary pressure–flow relation, as well as the influence of cardiac function on it, bears great clinical significance. The interaction of a coronary stenosis with the coronary pressure–flow relation can be understood from the stenosis pressure drop–flow velocity relationship. Based on these relationships the clinically applied concepts of coronary flow velocity reserve, fractional flow reserve, stenosis resistance and microvascular resistance are discussed. Attention is further paid to the heterogeneous nature of myocardial perfusion, the vulnerability of the subendocardium and the role of collateral flow on hyperemic coronary pressure–flow relations. This article is part of a Special Issue entitled “Coronary Blood Flow”.

► Hyperemic coronary pressure–flow relations are curvilinear, expressing pressure and cardiac contraction effects.
► Hyperemic coronary perfusion is heterogeneous, with subendocardium especially at risk for underperfusion.
► Physiological indices are preferable over angiographically derived stenosis parameters for clinical decision making.
► Combined pressure and flow velocity data comprehensively assess both epicardial and microvascular compartments.
► Coronary resistance adapts to lowered perfusion pressure distal to a stenosis by microvascular remodeling.