Precise assessment of lesion severity is fundamental for the clinical decision making in the patients with coronary artery disease. Coronary angiography has limitation to projection imaging techniques. Intravascular ultrasound (IVUS) has been known to be a gold standard of morphological severity of coronary stenosis. Fractional flow reserve (FFR) is known to be a lesion specific functional index of epicardial stenosis that can be derived from intracoronary pressure assessed during maximal vasodilation. The objective of this study was to investigate the validity of fractional flow reserve for stenosis severity in comparison with IVUS.

The study population consisted of 24 patients with angina pectoris (M:F=19:5, age: 58±12 yrs). The IVUS and intracoronary pressure wire performed at 26 lesions after diagnostic coronary angiography. We measured angiographical diameter stenosis (DST), minimal luminal diameter (MLD), minimal luminal area (MLA) and reference area stenosis (r-AST). FFR was defined by the ratio of distal mean coronary pressure (Pd) to aortic mean pressure (Pa).

FFR showed significant correlation with both r-AST (r=-0.93, p<0.00001) than DST (r=-0.79, p<0.0001). When the lesions with MLD less than 1.1 mm were excluded, considering the limitation of IVUS for the thickness of its catheter, FFR showed excellent correlation with r-AST with higher correlation coefficient (r=-0.96, p<0.00001). FFR showed significant correlation with MLA (r=0.87, p=0.0001) or MLD (r=0.83, p=0.0005).

FFR with excellent correlation with r-AST measured by IVUS seems to be a useful lesion specific functional index for the assessment of coronary stenosis in angina patients.