Introduction In recent years, intravascular ultrasound (IVUS) has evolved as a valuable adjunct to angiography. IVUS allows precise tomographic measurement of lumen area and plaque size, distribution and, to some extent, composition. It is essential in clinic decision making. Myocardial fractional flow reserve (FFR_myo) is a special index of the functional severity of coronary stenosis. Although the application of FFR_myo to assess intermediate coronary lesion is widely performed in some centers in developed countries, its use in China was lagged. Because it is relatively expensive to measure FFR_myo, it will be beneficial to save the expenses and to short operation time if CAG and IVUS criteria could be clinically used as tools to discriminate functional significant of intermediate stenosis.

Materials and Methods In 46 lesions of intermediate severity (eg, 40%–60% diameter stenosis) we assessed 1. by pressure wire: myocardial fractional flow reserve (FFR_myo, index of functional significance), and 2. by IVUS: minimal lumen cross-sectional area (MLA) and percent area stenosis at the lesion site. Receiver operating characteristic (ROC) curve analysis was performed to establish the best cut-off values of IVUS indexes (ie, MLA and percent area stenosis) that were most predictive of FFR_myo<0.75.

Results FFRmyo in 46 lesions of angiographic intermediate stenosis (49±11%) was significantly lower than it was in angiographic normal artery (0.83±0.15 vs 0.97±0.02, p<0.01). Fourteen lesions (30%) were functionally critical (eg, FFR_myo<0.75). By regression analysis, percent area stenosis had a significant inverse correlation with FFR_myo (r=−0.68, p<0.01). MLA showed a significant positive relation with FFR_myo (r=0.63, p<0.01). By ROC analysis, we identified an IVUS area stonosis ≥65% (sensitivity 100%, specificity 72%), a minimal lumen cross-sectional area ≤4 mm² (sensitivity 93%, specificity 77%) to be the best cut-off values to fit with FFR_myo<0.75.

Conclusion IVUS area stenosis ≥65% and minimal lumen cross-sectional area ≤4 mm² reliably identified functionally critical intermediate coronary stenosis.