An index of physiological significance of coronary stenosis: defined as the ratio of maximal blood flowis a stenotic artery to a normal maximal flow.

Fractional flow reserve performed during invasive coronary angiography provides lesion specific data on ischemia which when used to direct revascularization procedures, leads to improved clinical outcomes.

Trials have shown the benefit of calculating fractional flow reserve (FFR; the ratio, at maximum hyperemia of the main arterial blood pressure measured distal to stenosis to the main pressure measured before the stenosis) with a coronary pressure wire to evaluate the physiological importance of coronary artery lesions and guide revascularization decisions, in patients with coronary artery disease.

It is an invasive measurement using coronary angiography to assess the potential of a coronary stenosis to induce myocardial ischemia.

Fractional flow reserve (FFR) is the ratio of the mean coronary artery pressure distal to an obstructive coronary lesion relative to the mean aortic pressure during maximum coronary blood flow and represents a physiologic measure of coronary stenosis.

In patients with intermediate stenosis being evaluated for PCI, FFRB guidance was not inferior to IV ultrasound guidance with respect to composite outcomes of death, myocardial infarction, or revascularization at 24 months.

Measured during coronary angiography by calculating the ratio of distal coronary pressure measured with a coronary pressure guidewire to aortic pressure measured simultaneously with a catheter.

It is readily calculated in the heart catheterization laboratory by measuring the pressure gradient across stenosis during reactive hyperemia.

A pressure wire based index used during coronary angiography assessing potential of coronary stenosis to induce myocardial ischemia.

In a normal coronary artery is 1.0.

A value of 0.8 or less identifies ischemic associated coronary artery stenosis and has an accuracy of more than 90% (Pijls).

Fractional flow reserve is a pressure derived measure of maximal myocardial blood flow beyond stenosis divided by theoretical normal maximal flow in the absence of stenosis, such as fractional flow reserve in a vessel with no obstruction is 1.0.

Fractional flow reserve is a reproducible, lesion specific measure of stenosis severity that correlates with determined ischemia by non-invasive testing.

Fractional flow reserve is measured by advancing a pressure sensor beyond the stenosis in question and measuring vasodilating in the resistance vessels by administering a potent vasodilator usually adenosine.

Revascularization procedures of lesions below .80 results in better outcomes than does medical therapy.

PCI is not recommended for nonischemic functional flow reserve lesions of greater than 0.80 because it is not been demonstrated to be beneficial and may even be harmful.

Fractional flow reserve values of 0.75 or less reliably correlate with objective ischemia, whereas values of more than 0.8 rarely do, regardless of the angiographic appearance of the coronary artery.

The benefit of PCI as initial treatment patients with stable coronary artery disease is controversial as the result depends on the extent and degree of myocardial ischemia.

Fractional flow reserve value of 0.8 or less, as measured with coronary pressure wire during catheterization, indicates potential of a stenosis to induce myocardial ischemia.

In the study of 1220 patients with stable coronary artery disease FFR (fractional flow reserve)-guided PCI as compared with medical therapy alone, improves the outcome (De Bruyne B et al ).

Provides information similar to myocardial perfusion but is more specific analyzing separately segments or coronary arteries and prevents the masking of ischemic areas.

FFR is measured at a steady state and can be followed with a vasodilator such as adenosine, that causes hyperemic flow that results in an invasive pharmacological stress test.

Deferring the placement of stents in lesions assessed by FFR results in an annual rate of death or myocardial infarction of 1% in patients with single coronary artery disease, which is a lower percentage than associated with routing stenting.

In patients with stable coronary artery disease and functionally significant stenosis a fractional flow reserve guided PCI plus the best available medical therapy, as compared with the best medical therapy alone, decreased the need for urgent revascularization. (FAME 2 trial investigators).

In the above study, patients without ischemia, the outcome appeared to be favorable with the best available medical therapy alone.

The benefit of PCI as initial treatment patients with stable coronary artery disease is controversial as the result depends on the extent and degree of myocardial ischemia.

Fractional flow reserve value of 0.8 or less, as measured with coronary pressure wire during catheterization, indicates potential of a stenosis to induce myocardial ischemia.

In the study of 1220 patients with stable coronary artery disease FFR (fractional flow reserve)-guided PCI as compared with medical therapy alone, improves the outcome (De Bruyne B et al ).

In a retrospective study of 9106 patients with PCI as compared with no PCI was significantly associated with a lower rate of major adverse cardiac events at five years among patients with ischemic FFR measurements (31.5% versus 39.1%) and a higher rate of major adverse cardiac events at five years among patients with nonischemic FFR measurements at 33.3% versus 24.4% (Sud M).

In patients with chronic coronary syndrome or acute coronary syndrome with out ST- segment elevation, the use of fractional flow reserve measurement during percutaneous coronary intervention to assess the functional severity of coronary lesions, results in a lower risk of major cardiovascular events than myocardial revascularization guided by angiography.

Among patients with ST-segment elevation myocardial infarction (STEMI) and multivessel disease, complete revascularization of non-culprit lesions guided by FFR or angiography results in lower frequency repeat revascularization than revascularization of only the culprit lesion.

However, in patients with STEMI undergoing complete revascularization, FFR guided strategy did not have a significantly benefit over angiographic guided strategy with respect to risk of death, myocardial infarction, urgent revascularization at one year.

Among patients with STEMI, or high-risk, NSTEMI multivessel coronary artery disease, FFR guided revascularization did not show a lower risk of composite death from any cause, myocardial infarction, or unplanned revascularization, than culprit lesion only PCI at 4.8 years (FULL REVASC Trial investigators).

Among patients with STEMI who have undergone successful primary PCI, immediate instantaneous wave free ratio guided PCI was not superior to deferred cardiac stress, MRI guided PCI of non-culprit coronary artery lesions with respect to death from any cause, recurrent myocardial infarction or hospitalization for heart failure at three years (iMODERN investigators).

In patients with three vessel coronary artery disease, FFR guided PCI was not inferior to CABG with respect to the incidence of a composite of death, myocardial infarction, stroke or repeat revascularization at one year (FAME 3 investigators).

In a randomized clinical trial of 478 patients, a significant reduction in composite outcome of all-cause death, non-fatal myocardial infarction, any revascularization, and stroke at one year in the complete revascularization group was found compared with culprit, only revascularization supporting the use of fractional flow reserve guided complete revascularization during the index procedure in patients with non-ST-segment elevation myocardial infarction and multivessel disease (Pustgens T).

Angio-based (angiography) FFR estimates FFR from angiographic images (often with 3D reconstruction/flow modeling) without using a pressure wire to measure intracoronary pressure during the procedure.

Pressure-wire–guided FFR is the gold standard physiology test: a pressure sensor-tipped wire measures intracoronary pressure during hyperemia (e.g., adenosine), and FFR is calculated from pressure ratios (typically Pd/Pa).

Among patients with intermediate, coronary artery lesions undergoing physiological assessment in the catheterization lab, angiography guided strategy involving FFR angio was non-inferior to a pressure wire guided strategy with respect to a composite end point of death, myocardial infarction, or unplanned clinically indicated coronary revascularization at one year (ALL-RISE Investigators).

CT-derived Fractional Flow Reserve is a noninvasive technique that estimates the functional significance of a coronary artery blockage using a standard CT coronary angiogram, without needing an invasive catheter procedure.

A coronary CT angiogram (CCTA) is performed as usual.

The images are sent to specialized software (e.g., HeartFlow )

The software builds a 3D model of the coronary arteries and uses computational fluid dynamics (CFD) to simulate blood flow.

It calculates the FFR value at any point along the artery — a number between 0 and 1 representing the pressure drop across a stenosis.

– FFR-CT ≤ 0.80 → suggests the blockage is functionally significant (likely limiting blood flow, potential candidate for stenting/intervention) – FFR-CT > 0.80 → suggests the blockage is not causing significant flow limitation, so intervention may not be needed even if the stenosis looks anatomically severe on CT

Traditional invasive FFR requires threading a pressure wire into the artery during a cath procedure, plus a drug (adenosine) to induce hyperemia.

FFR-CT gets similar functional information from images already taken, avoiding an invasive test in patients who may not need one.

Helps distinguish “flow-limiting” blockages from ones that look bad on anatomy alone but aren’t actually starving the heart muscle of blood.

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