What can intracoronary pressure measurements tell us about flow reserve? Pressure-Bounded coronary flow reserve and example application to the randomized DEFER trial.

Abstract

We propose a novel technique called pressure-bounded coronary flow reserve (pb-CFR) and demonstrate its application to the randomized DEFER trial. Intracoronary flow reserve assessment remains underutilized relative to pressure measurements partly due to less robust tools. While rest and hyperemic intracoronary pressure measurements cannot quantify CFR exactly, they do provide upper and lower bounds. We validated pb-CFR invasively against traditional CFR, then applied it to high fractional flow reserve (FFR ≥ 0.75) lesions in DEFER randomized to revascularization or medical therapy. pb-CFR showed an 84.4% accuracy to predict invasive CFR < 2 or CFR ≥ 2 in 107 lesions. In its proof of concept application to DEFER lesions with FFR ≥ 0.75, the 28 with pb-CFR < 2 compared to 28 with pb-CFR ≥ 2 had a non-significant reduction in freedom from angina (61% vs. 71% at 5 years, P = 0.57) and a non-significantly higher rate of major adverse cardiac events (MACE, 25% vs. 15%, P = 0.34). Lesions with FFR ≥ 0.75 but pb-CFR < 2 showed no difference in freedom from angina (61% vs. 50%, P = 0.54) or MACE (25% vs. 38%, P = 0.27) between the 28 randomized to medical therapy and the 16 randomized to revascularization. pb-CFR offers a new method for studying FFR/CFR discordances using regular pressure wire measurements. As an example application, DEFER suggested that low pb-CFR with high FFR may be a risk marker for more angina and worse outcomes, but that this risk cannot be modified by revascularization. © 2017 Wiley Periodicals, Inc.