Role of variability in microvascular resistance on fractional flow reserveand coronary blood flow velocity reserve in intermediate coronary lesions

Background-Fractional flow reserve (FFR) and coronary blood flow velocity r eserve (CFR) represent physiological quantities used to evaluate coronary l esion severity and to make clinical decisions. A comparison between the out comes of both diagnostic techniques has not been performed in a large cohor t of patients with intermediate coronary lesions, Methods ann Results-FFR and CFR were assessed in 126 consecutive patients w ith 150 intermediate coronary lesions (between 40% and 70% diameter stenosi s by visual assessment). Agreement between outcomes of FFR and CFR, categor ized at cut-off values of 0.75 and 2.0, respectively, was observed in 109 c oronary lesions (7340), whereas discordant outcomes were present in 41 lesi ons (27%). In 26 of these 41 lesions, FFR was <0.75 and CFR<greater than or equal to>2.0 (group A); in the remaining 15 lesions, FFR was greater than or equal to0.75 and CFR(2.0 (group B). Minimum microvascular resistance, de fined as the ratio of mean distal pressure to average peak blood flow veloc ity during maximum hyperemia, showed a large variability (overall range, 0. 65 to 4.64 mm Hg . cm(-1). s(-1)) and was significantly higher in group B t han in group A (2.42+/-0.77 versus 1.91+/-0.70 mm Hg . cm(-1).s(-1); P=0.03 4) Conclusions-Our findings demonstrate the prominent role of microvascular re sistance in modulating the relationship between FFR and CFR and emphasize t he importance of combined pressure and flow velocity measurements to evalua te coronary lesion severity and microvascular involvement.