Background-—Coronary microcirculatory dysfunction portends a poor cardiovascular outcome. Invasive assessment of
microcirculatory dysfunction by coronary flow reserve (CFR) and hyperemic microvascular resistance (HMR) is affected by
coronary artery disease (CAD). In this study we propose minimal microvascular resistance (mMR) as a new measure of
microcirculatory dysfunction and aim to determine whether mMR is influenced by CAD.
Methods and Results-—We obtained 482 simultaneous measurements of intracoronary Doppler flow velocity and pressure. The
mMR is defined as the ratio between distal coronary pressure and flow velocity during the hyperemic wave-free period.
Measurements were divided into 2 cohorts. Cohort 1 was a paired analysis involving 81 pairs with a vessel with and without CAD to
investigate whether HMR, CFR, and mMR are modulated by CAD. CFR was lower, and HMR was higher, in vessels with CAD than in
vessels without CAD: 2.12 0.79 versus 2.56 0.63 mm Hgcm 1
s, P<0.001, and 2.61 1.22 versus 2.31 0.89 mm Hgcm 1
s,
P=0.04, respectively. mMR was equal in vessels with and without CAD: 1.54 0.77 versus 1.53 0.57 mm Hgcm 1
s, P=0.90.
Differences for CFR occurred when FFR was 0.60 to 0.80 or ≤0.60 but not when FFR ≥0.80. For HMR, the difference occurred only
when FFR ≤0.60. For mMR, no difference was observed in any FFR stratum. Cohort 2 was used for validation and showed significant
relationships for CFR and HMR with FFR: Pearson r=0.488, P<0.001 and 0.159, P=0.03, respectively; mMR had no association
with FFR: Pearson r=0.055; P=0.32.
Conc