Figure 10.

Conceptual plot of the fractional flow reserve (FFR)–coronary flow velocity reserve (CFVR) relationship. Four main quadrants can be identified by applying the clinically applicable cut-off values for FFR and CFVR, indicated by the dotted lines. Patients in the upper right blue area are characterized by concordantly normal FFR and CFVR, and patients in the red lower left area are characterized by concordantly abnormal FFR and CFVR. Patients in the upper left orange area and lower right light green area are characterized by discordant results between FFR and CFVR, where the combination of an abnormal FFR and a normal CFVR indicates predominant focal epicardial, but nonflow-limiting, coronary artery disease, and the combination of a normal FFR and an abnormal CFVR indicates predominant microvascular involvement in coronary artery disease. The small dark green region in the lower right is characterized by an FFR near 1 and an abnormal CFVR, indicating sole involvement of the coronary microvasculature. The FFR gray zone indicates the equivocal 0.75 to 0.80 FFR range. Adapted from van de Hoef TP, Circ Cardiovasc Interv. 2014 Jun;7(3):301–11.⁹⁹