Objectives: Fractional flow reserve(FFR) and hyperemic epicardial stenosis resistance index(hESRI) had been applied to evaluate the functional severity of epicardial coronary stenosis. However, the influence of microvascular integrity to FFR and hESRI is not clearly defined. Methods: Sixty-five intermediate lesions of 57 patients(age: 59±11, male: 50 patients, IRA: 17) were studied. IVUS % area stenosis(r-%AS), FFR, coronary flow reserve(CFR) and hESRI were measured. Hyperemic microvascular resistance index(hMVRI) of the distal to lesion was measured after PCI. Sixty-five studied lesions were divided into two groups(Group 1, hMVRI≤2.09, n=42; Group 2, hMVRI>2.09 mmHgㆍcm-1ㆍsec, n=23; 2.09 is best cutoff value(BCV) for CFR 2.5). Results: There was not significant difference in r-%AS between two groups(group 1 vs. group 2: 75.5±9.8% vs. 74.5±9.1%, p=0.703). However, FFR was significantly higher(0.80±0.10 vs. 0.69±0.15, p=0.002) in group 2 than group 1. hESRI was lower in Group 2 than Group 1, however, the result was not significant statistically(0.70±0.48 vs. 0.99±0.83, p=0.087). In group 1, BCV of FFR and hESRI for 75% of r-%AS were 0.75 and 0.64(sensitivity 88.5%, specificity 81.2%, AUC 0.853; sensitivity 83.3%, specificity 87.5%, AUC 0.868, respectively), respectively. However, in group 2, those values were 0.83 and 0.51(sensitivity 76.9%, specificity 90.0%, AUC 0.827; sensitivity 76.9%, specificity 80.0%, AUC 0.785), respectively. Concordance rate between FFR and r-AS% in group 1 was 85.7%(sensitivity 88.5%, specificity 81.3%, p<0.001; κ=0.697, p<0.001). However, in group 2, that value was 65.2%(sensitivity 41.7%, specificity 90.9%, p=0.155; κ=0.319, p=0.076). Conclusion: FFR was affected by hMVRI of the distal to lesion and may be underestimated to assess the coronary stenosis severity in the cases of increased microvascular resistance of the distal segment of the lesion.
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