Coronary physiological assessment combining fractional flow reserve and index of microcirculatory resistance in patients undergoing elective percutaneous coronary intervention with grey zone fractional flow reserve

The aim of this study is to investigate the association between fractional flow reserve (FFR) values and change in coronary physiological indices after elective percutaneous coronary intervention (PCI).Decision making for revascularization when FFR is 0.75-0.80 is controversial.A retrospective analysis was performed of 296 patients with stable angina pectoris who underwent physiological examinations before and after PCI. To investigate the differences of coronary flow improvement between territories with low-FFR (<0.75) and grey-zone FFR (0.75-0.80), serial changes in physiological indices including mean transit time (Tmn), coronary flow reserve (CFR), and index of microcirculatory resistance (IMR) were compared between these two groups.Compared to low-FFR territories, grey-zone FFR territories showed significantly lower prevalence of Tmn shortening, CFR improvement, and decrease in IMR (Tmn shorting, 63.9% vs. 87.0%, P < .001; CFR improvement, 63.0% vs. 75.7%, P = .019; IMR decrease, 51.3% vs. 63.3%, P = .040) and lower extent of their absolute changes (Tmn shorting, 0.06 (-0.03 to 0.16) vs. 0.22 (0.07-0.45), P < .001; CFR improvement, 0.45 (-0.32 to 1.87) vs. 1.08 (0.02-2.44), P < .01; IMR decrease, 0.2 (-44.0 to 31.3) vs. 2.9 (-2.9 to 11.8), P = .022). Multivariate analysis showed that pre-PCI IMR predicted improved coronary flow profile in both groups, whereas pre-PCI FFR predicted increased coronary flow indices in low-FFR territories.Worsening of physiological indices after PCI was not uncommon in territories showing grey-zone FFR. Physiological assessment combining FFR and IMR may help identify patients who may benefit by PCI, particularly those in the grey zone.