BackgroundExperimental studies have shown that fractional flow reserve (defined as the ratio of maximal achievable flow in a stenotic area to normal maximal achievable flow) can be calculated from coronary pressure measurements only. The objectives of this study were to alidate fractional flow reserve calculation in humans and to compare this information with that derived from quantitative coronary angiography.Methods and ResultsTwenty-two patients with an isolated, discrete proximal or mid left anterior descending coronary artery stenosis and normal left ventricular function were studied. Relative myocardial flow reserve, defined as the ratio of absolute myocardial perfusion during maximal vasodilation in the stenotic area to the absolute myocardial perfusion during maximal vasodilation (adenosine 140 jig. μkg−1· min−1intravenously during 4 minutes) in the contralateral normally perfused area, was assessed by15O-labeled water and positron emission tomography (PET). Myocardial and coronary fractional flow reserve were calculated from mean aortic, distal coronary, and right atrial pressures recorded during maximalvasodilation. Distal coronary pressures were measured by an ultrathin, pressure-monitoring guide wire with minimal influence on the transstenotic pressure gradient. Minimal obstruction area, percent area stenosis, and calculated stenosis flow reserve were assessed by quantitative coronary angiography.There was no difference in heart rate, mean aortic pressure, or rate-pressure product during maximal vasodilation during PET and during catheterization. Percent area stenosis rangedfrom 40% to 94% (mean, 77±13%), myocardial fractional flow reserve from 0.36 to 0.98 (mean, 0.61±0.17), and relative flow reserve from 0.27 to 1.23 (mean, 0.60±0.26). A close correlationwas found between relative flow reserve obtained by PET and both myocardial fractional flow reserve (r= .87) and coronary fractional flow reserve obtained by pressure recordings (r= .86). The correlations between relative flow reserve obtained by PET and stenosis easurements derived from quantitative coronary angiography were markedly weaker (minimal obstruction area,r= .66; percent area stenosis,r= − .70; and stenosis flow reserve,r= .68).ConclusionsFractional flow reserve derived from pressure measurements correlates more closely to relative flow reserve derived from PET than angiographic parameters. This validates in humans the use of fractional flow reserve as an index the physiological consequences of a given coronary artery stenosis.