884 Size of Low Wall Shear Stress Areas in Coronary Arteries is Related to the Epicardial Coronary Physiology Indices

Wall shear stress (WSS) plays an important role in coronary atherosclerosis. Low WSS is associated with progression of atherosclerosis, while high WSS leads to vulnerable plaque transformation. No study has evaluated the relationship between WSS and coronary physiology indices. Patients were prospectively recruited and fractional flow reserve (FFR), coronary flow reserve (CFR), and index of microcirculatory resistance (IMR) were measured. The non-hyperaemic pressure ratios (NHPRs) including resting full-cycle ratio (RFR), resting distal/aortic pressure (Pd/Pa), instantaneous wave-free ratio (iFR), diastolic pressure ratio (dPR) and diastolic hyperaemia-free ratio (DFR) were derived offline. FFR ≤0.80, NHPR ≤0.89, CFR <2, or IMR >25 were considered ischaemic/abnormal. Computational fluid dynamics analysis was performed and the lesion WSS, sub-segment WSS, and the total area of low WSS (defined as <1 Pa) calculated (Figure A). Of the 112 vessels from 93 patients, total area of low WSS was significant larger in lesions with ischaemic FFR (72 vs 28mm2, p<0.001), RFR (64 vs 27 mm2, p<0.001), Pd/Pa (83 vs 30 mm2, p<0.001), iFR (64 vs 26 mm2, p<0.001), DPR (66 vs 27 mm2, p<0.001), DFR (68 vs 28 mm2, p<0.001), and CFR (81 vs 35 mm2, p<0.001) values (Figure B). Proximal WSS was significant higher in lesions with ischaemic FFR, iFR, and dPR values (all 4.2 vs 3.3 Pa, p=0.04). Functionally significant coronary lesions have significantly larger total area of low WSS and higher proximal WSS which may explain the increased cardiovascular event rates in patients with ischaemic lesions.