[Coronary microvascular resistance and its relevant factors in patients with moderate coronary stenosis and chest pain]

Objective: To evaluate the impact of cardiovascular risk factors on index of microvascular resistance (IMR) and coronary flow reserve (CFR) and to explore the characteristics of IMR and CFR and the relationship between IMR and angiographic features in patients with intermediate coronary stenosis and chest pain. Methods: Fractional flow reserve (FFR), CFR, and IMR were measured in patients who underwent invasive coronary angiography with 40%-70% stenosis by visual assessment. All patients with FFR>0.75 were enrolled and grouped with the cut-off points of IMR≥25 and CFR≤2.0. Patients with IMR≥25 were group H, including two sub-groups (high IMR-low CFR, group H₁ and high IMR-high CFR, group H₂), while those with IMR<25 were group N. The thrombolysis in myocardial infarction (TIMI) frame were counted. Results: A total of 34 patients with FFR>0.75 were enrolled with 61.8%(21 cases) of males and 38.2% (13 cases) of females. The mean age was (57.3±8.1) years old. High IMR accounted for 47.1% of all cases. There was significant difference between group H and N in TIMI frame (33.0 vs. 20.8, P=0.031). There were significant differences between group H₁ and H₂ in homocysteine (17.8 µmol/L vs. 12.0 µmol/L, P=0.005) and IMR_corr (58.0 vs. 36.1, P=0.002). IMR_corr was correlated to TIMI frame (r=0.40, P=0.012) for all cases. The sensitivity and specificity of inferring IMR≥35.3 by TIMI frame were 0.75 and 0.65 (P=0.049) with TIMI frame over 40.5. Conclusions: High IMR may be one of the reasons for chest pain in patients with intermediate coronary stenosis. There is no correlation between vascular risk factors and IMR or CFR, while there is positive correlation between TIMI frame and IMR. The specificity is 65% for inferring IMR rise with TIMI frame over 40.5.