The angiogram is a 2-dimensional image of 3-dimensional structures. Most intermediate lesions are oval shaped with 2 diameters, 1 narrow and 1 wide dimension. The angiogram of an eccentric lesion cannot reliably indicate flow adequacy. Other lesions (lower right) may appear hazy but widely patent, only to be responsible for angina due to plaque rupture, as demonstrated by intravascular ultrasound cross-section (far right corner). Figure illustration by Rob Flewell.

The angiographic 2-dimensional images cannot account for the multiple factors that produce resistance to coronary blood flow and loss of pressure across a stenosis. The eccentric and irregular stenosis (upper panel) shows arrows designating entrance effects, friction, and zones of turbulence accounting for separation energy loss. The calculation of pressure loss (P) across a stenosis (lower right panel) incorporates length (l), areas stenosis (A_s), reference area (A_n), flow (Q), and coefficients of viscous friction and laminar separation (f₁ and f₂) as contributors to resistance and hence pressure loss. Figure illustration by Rob Flewell.

Phasic and mean pressure signals used to measure fractional flow reserve (FFR), calculated as the ratio of distal coronary pressure (Pd) to aortic pressure (Pa) at maximal hyperemia, which is equal to 0.78 in this example. For reference to coronary flow, a velocity signal is shaded and shown at the bottom to identify the time of maximal hyperemia. The velocity signal is only available in combined sensor wire studies. Courtesy of Dr. Bernard DeBruyne. CVR = coronary vasodilatory reserve.

Pressure wire transducer located at arrow. Lower panel shows phasic and mean aortic and distal coronary pressure with significant pressure loss during hyperemia. Fractional flow reserve (FFR) is 75/110 = 0.68.

(Left) Event-free survival curves for the Defer, Perform, and Reference groups. (Right) Incidence of cardiac death/myocardial infarction (MI) for the 3 groups. Reprinted, with permission, from Pijls et al. (40).

(A) Event-free survival for major adverse cardiac events was significant at 1 year. No differences in event-free survival for death (B), myocardial infarction (C), or coronary artery bypass grafting/percutaneous coronary intervention (PCI) (D). Reprinted, with permission, from Tonino et al. (11).

(A) Cine angiograms and FFR in a patient undergoing multivessel assessment. (Left) Right coronary artery with diffuse severe disease. (Middle) First obtuse marginal (OM1) shows FFR = 0.76. (Right) Left anterior descending artery (LAD) FFR = 0.85. Intervention on right coronary artery, OM, was performed. (B) Angiographic results of PCI guided by FFR. Abbreviations as in Figure 1.

Fractional flow reserve (FFR) was 0.87. Medical therapy was recommended. Pa = aortic pressure; Pd = mean pressure distal to a stenosis.

Serial changes of fractional flow reserve (FFR) in the side branch vessel of 22 bifurcation lesions after stenting main vessel (Post-stent), after kissing balloon inflation of main vessel and side branch (Post-KB), and at 6 months' follow-up. Reprinted, with permission, from Koo et al. (58).

(A) The relationship between angiographic stenosis severity and graft failure after angiographic follow-up at 1 year. (B) The relation between functional stenosis severity established by fractional flow reserve (FFR) measurements and graft failure at angiographic follow-up after 1 year. Reprinted, with permission, from Botman et al. (59).

(A) Concordance between fractional flow reserve (FFR) and single-photon emission computed tomography (SPECT) (dipyridamole-stress paired with rest imaging). (B) Concordance between FFR and myocardial contrast echo (MCE). (C) Sensitivity and specificity curves of FFR for detecting reversibility of combined noninvasive testing in patients with acute coronary syndrome. Reprinted, with permission, from Samady et al. (36). DS = diameter stenosis.