Microvascular resistance reserve before and after PCI: a serial FFR and [15O] H2O PET study

Background and aims Microvascular Resistance Reserve (MRR) has recently been introduced as a microvasculature-specific index and hypothesized to be independent of coronary stenosis. The aim of this study was to investigate the change of MRR after percutaneous coronary intervention (PCI). Methods In this post-hoc analysis from the PACIFC trials symptomatic patients underwent [15O]H2O positron emission tomography (PET) and invasive fractional flow reserve (FFR) before and after revascularization. Coronary flow reserve (CFR) from PET and invasive FFR were used to calculate MRR. Results Among 52 patients (87% male, age 59.4±9.4 years), 61 vessels with a median FFR of 0.71 (95% confidence interval: 0.55 to 0.74) and a mean MRR of 3.80±1.23 were included. Following PCI, FFR, hyperemic myocardial blood flow (hMBF) and CFR increased significantly (All p-values <0.001). MRR remained unchanged after PCI (3.80±1.23 before PCI versus 3.60±0.97 after PCI; p=0.23). In vessels with a pre-PCI FFR ≤0.70 pre- and post-PCI MRR were 3.90±1.30 and 3.73±1.14 (p=0.56). Similar findings were observed for vessels with a FFR between 0.71-0.80 (pre-PCI MRR 3.70±1.17 vs. post PCI MRR 3.48±0.76, p=0.19). Conclusions Our study indicates that MRR, assessed using a hybrid approach of PET and invasive FFR, is independent of the severity of epicardial stenosis. These findings suggest that MRR is a microvasculature-specific parameter.