Relationship between FFR, CFR and coronary microvascular resistance – Practical implications for FFR-guided percutaneous coronary intervention

Abstract

ObjectiveThe aim was threefold: 1) expound the independent physiological parameters that drive FFR, 2) elucidate contradictory conclusions between fractional flow reserve (FFR) and coronary flow reserve (CFR), and 3) highlight the need of both FFR and CFR in clinical decision making. Simple explicit theoretical models were supported by coronary data analyzed retrospectively.MethodologyFFR was expressed as a function of pressure loss coefficient, aortic pressure and hyperemic coronary microvascular resistance. The FFR-CFR relationship was also demonstrated mathematically and was shown to be exclusively dependent upon the coronary microvascular resistances. The equations were validated in a first series of 199 lesions whose pressures and distal velocities were monitored. A second dataset of 75 lesions with pre- and post-PCI measures of FFR and CFR was also analyzed to investigate the clinical impact of our hemodynamic reasoning.ResultsHyperemic coronary microvascular resistance and pressure loss coefficient had comparable impacts (45% and 49%) on FFR. There was a good concordance (y = 0.96 x − 0.02, r2 = 0.97) between measured CFR and CFR predicted by FFR and coronary resistances. In patients with CFR < 2 and CFR/FFR ≥ 2, post-PCI CFR was significantly >2 (p < 0.001), whereas it was not (p = 0.94) in patients with CFR < 2 and CFR/FFR < 2.ConclusionThe FFR behavior and FFR-CFR relationship are predictable from basic hemodynamics. Conflicting conclusions between FFR and CFR are explained from coronary vascular resistances. As confirmed by our results, FFR and CFR are complementary; they could jointly contribute to better PCI guidance through the CFR-to-FFR ratio in patients with coronary artery disease.

Impact of Revascularization on the Distal to Proximal Pressure Ratio in Case of Multiple Coronary Stenoses

“…So that each stenosis may independently have a pressure ratio higher than 0.8, but the product is lower than 0.8. Other groups already pointed out that the individual pressure ratio of a stenosis gets affected by the presence of other lesions or by the resistance of the supplied myocardium area [4,7,30,31,45,46].…”

“…Other difficulties may occur: complex anatomy, calcifications, motion artifacts, poor quality of the images… The 3-dimensional computations of flow and pressure in the diseased arteries rely on the resolution of Navier-Stokes equations, which are not exactly appropriate in the cases where turbulent flows exist. The other important point in the computed FFR approach is the boundary conditions applied at the end of the reconstructed vessels [5][6][7]. The microcirculatory bed resistances may be obtained from scaling laws of branches, relating organ size to its perfusion rate [3], or they are chosen as averaged values coming from previous studies [4].…”

Coronary Tortuosity Overestimate The FFR&nbsp;Measurement In Stenotic Coronary Artery Model

“…Functional evaluation of coronary artery stenosis severity is important in clinical practice [4]. FFR is currently used as a gold standard for the assessment of functional significance of stenosis severity and is applied for guiding cardiovascular intervention [5].…”

Influence of microcirculation load on FFR in coronary artery stenosis model

“…And the coronary artery hemodynamics are affected both by the epicardial stenotic coronary artery impede and microcirculation load. Regulation of coronary blood flow is quite complex [1], epicardial stenosis severity and microcirculatory resistance may affect each other [2,3]. However, the complex interrelationship between the coronary microcirculation and the epicardial coronary arteries contributing to the coronary artery hemodynamics remains poorly understood and is controversial [4].…”