Objective       To determine the value of fraction flow reserve (FFR) in the diagnosis for long coronary artery lesions of with moderate stenosis and the effect of right atrial pressure (RAP) on FFR.        Methods       A total of 83 patients with at least one coronary artery with moderate stenosis according to the results of coronary arteriography (CAG) admitted in our department from September 2013 to July 2014 were recruited in this study. They were randomly divided into 3 groups based on the length of lesions

that is

group A with short lesions (20 mm，n=42)

group B with long lesions (20 to 35 mm，n=27) and group C with super long lesions (≥36 mm，n=14). Their FFR was determined

and then recalculated by incorporation of RAP into the calculation as FFRrap. For the patients with FFR0.75

they underwent percutaneous coronary intervention (PCI). For those with FFR0.80

they only received the optimal medical therapy. For those with FFR from 0.75 to 0.80

PCI was carried out on the patients with FFRrap0.75

and optimal medical therapy was given to those with FFRrap≥0.75. Major adverse cardiac events (MACE)

such as cardiac death

nonfatal myocardial infarction

angina

revascularization of target vessel and target lesion were followed up in 30 d after the therapy.       Results       FFR and FFRrap were significantly lower in the group C than the groups A and B (F=2.524

P=0.000; F=1.656

P=0.015). In every group

their FFRrap was significantly decreased than the value of FFR (group A: 0.84±0.19 vs 0.78±0.14

P0.05; group B: 0.75±0.14 vs 0.72±0.11

P0.05; group C: 0.67±011 vs 0.63±0.07

P0.05). There was no significant difference in the incidences of MACE in different groups in 3 months after PCI or the therapy. The total incidence of MACE was 13.3% in the cohort.       Conclusion       The longer the lesion of moderate coronary stenosis is

the lower the value of FFR is. When the value is from 0.75 to 0.80

FFRrap is more accurate to evaluate the distal blood flow of lesion and is helpful to guide the clinical treatment strategies.