The following are key points to remember from this review about fractional flow reserve (FFR) in clinical practice:

1. Invasive coronary wire-based FFR is routinely used for physiology-based coronary revascularization. Recently, quantitative flow ratio (QFR) has emerged as an alternative to conventional FFR.
2. QFR uses 3D geometric reconstruction of conventional angiographic and intravascular images. This technology computes a surrogate for FFR. Angiographic and intravascular image quality is therefore critical for QFR measurement.
3. A major challenge with QFR assessment is developing an accurate boundary condition reflecting the coronary blood flow dynamics. Therefore, diagnostic concordance between QFR and FFR is reduced in patients with microcirculatory dysfunction such as in a vessel supplying territories with prior myocardial infarction (MI).
4. Limited randomized data are currently available on the correlation between clinical outcome and QFR. Functional SYNTAX score calculated by QFR in a retrospective analysis of the SYNTAX II study indicated superior prediction of a patient-oriented composite endpoint in patients with multivessel disease, when compared with the classical anatomical SYNTAX score (area under the curve, 0.68 [0.50–0.87] vs. 0.56 [0.37–0.75]; p = 0.002).
5. Currently, QFR is not validated for routine use. However, QFR if validated in ongoing clinical trials such as FAVOR III, will allow for hemodynamic assessment with diagnostic angiography only.
6. Common scenarios where QFR will have increased utility is nonculprit vessel assessment in the setting of MI where conventional FFR is considered unreliable. QFR will also enable hemodynamic assessment of the entire coronary tree easier without having to wire all three coronary arteries in patients with three-vessel disease.

Clinical Topics: Acute Coronary Syndromes, Cardiac Surgery, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Interventions and ACS, Interventions and Imaging, Angiography, Echocardiography/Ultrasound, Nuclear Imaging

Keywords: Acute Coronary Syndrome, Angiography, Cardiology Interventions, Coronary Angiography, Diagnostic Imaging, Fractional Flow Reserve, Myocardial, Hemodynamics, Microcirculation, Myocardial Infarction, Myocardial Ischemia, Myocardial Revascularization, Ultrasonography

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