Effects of Microvascular Integrity on the Evaluation of Fractional Flow Reserve and Epicardial Stenosis Resistance Index

Abstract

Background and Objectives：The fractional flow reserve (FFR) and the hyperemic epicardial stenosis resistance index (hESRI) are known to be useful indexes for evaluating the hemodynamic severity of an epicardial coronary stenosis. However, the influence of the microvascular integrity of the distal segment of the lesion on the FFR and hESRI has not been clearly defined.

Subjects and Methods：A total of fifty-nine intermediate lesions of 51 patients (mean age: 58±11, 13 infarct-related arteries (IRA)) were studied. The area of stenosis (r-AS%) on the IVUS, the FFR, the coronary flow reserve (CFR) and the hESRI were measured before and after PCI. The hyperemic microvascular resistance index (hMVRI) of the distal site of the lesion was measured after PCI. The studied lesions were divided into two groups (Group 1, post-stent hMVRI≤2.09 mmHgㆍcm-1ㆍsec, n=38; Group 2, post-stent hMVRI>2.09 mmHgㆍcm-1ㆍsec, n=21; 2.09 is the best cutoff value (BCV) for a CFR of 2.5).

Results：The FFR and hESRI had excellent correlation with the r-AS% (group 1: r=0.767, p<0.001; r=0.740, p<0.001; group 2: r=0.680, p=0.004; r=0.713, p=0.002, respectively). Although no significant difference was found in the r-AS% between the two groups, the FFR was significantly lower in group 1 (0.69±0.14 vs. 0.79±0.10, p=0.004). In group 1, the BCV of the FFR and hESRI for a r-%AS of 75% were 0.75 and 0.64, respectively, and the concordance rates were 86.8% (κ=0.721, p<0.001) and 81.6% (κ=0.627, p<0.001), respectively. However, in group 2, the BCV of the FFR and hESRI for an r-%AS of 75% were 0.83 and 0.50, respectively, and the concordance rates were 61.9% (κ=0.282, p=0.125) and 66.7% (κ=0.364, p=0.061), respectively.

Conclusion：The FFR and hESRI were significantly affected by the microvascular integrity of the distal segment of the lesion and the anatomic severity of the coronary stenosis was underestimated in the cases with microvascular dysfunction.