BACKGROUND: Patients with severe aortic stenosis frequently have coexisting coronary artery disease. Invasive hyperemic and nonhyperemic pressure indices are used to assess coronary artery disease severity but have not been evaluated in the context of severe aortic stenosis. METHODS: We compared lesion reclassification rates of fractional flow reserve (FFR) and resting full-cycle ratio (RFR) measured before and 6 months after transcatheter aortic valve implantation using the conventional clinical cutoffs of ≤0.80 for FFR and ≤0.89 for RFR. This was a substudy of the ongoing NOTION-3 trial (Third Nordic Aortic Valve Intervention). Two-dimensional quantitative coronary analysis was used to assess changes in angiographic lesion severity. RESULTS: Forty patients were included contributing 50 lesions in which FFR was measured. In 32 patients (36 lesions), RFR was also measured. There was no significant change in diameter stenosis from baseline to follow-up, 49.8% (42.9%-57.1%) versus 52.3% (43.2%-57.8%), P=0.50. RFR improved significantly from 0.88 (0.83%-0.93) at baseline to 0.92 (0.83-0.95) at follow-up, P=0.003, whereas FFR remained unchanged, 0.84 (0.81-0.89) versus 0.86 (0.78-0.90), P=0.72. At baseline, 11 out of 50 (22%) lesions were FFR-positive, whereas 15 out of 50 (30%) were positive at follow-up, P=0.219. Corresponding numbers for RFR were 23 out of 36 (64%) at baseline and 12 out of 36 (33%) at follow-up, P=0.003. CONCLUSIONS: In patients with severe aortic stenosis, physiological assessment of coronary lesions with FFR before transcatheter aortic valve implantation leads to lower reclassification rate at 6-month follow-up, compared with RFR.