Coronary flow reserve evaluation: basics, techniques and clinical applications

Coronary flow reserve is a useful physiologic parameter providing information on coronary stenoses severity. To date, the gold standard to evaluate coronary flow reserve consists of fractional flow reserve (FFR) measurement, assessed with a pressure-wire. The FFR has a high lesion specificity, due to insensitivity to patient hemodynamic status and to coronary microvascular resistance; it shows low inter- and intraindividual variability and a well-defined, bound cut-off range values (0.75-0.80). Several reports confirmed that FFR has high reproducibility and feasibility in patients with either single- or multi-vessel coronary artery disease, or with both stable and instable coronary artery disease and that is significantly associated with patient outcome. More recently, the FFR has been used as a sensitive marker of successful percutaneous coronary intervention, since postprocedural FFR value strongly predicts patients event-free survival rate after angioplasty. Moreover, it has been demonstrated that abnormal FFR ratios can be also associated with diffused atherosclerotic coronary artery disease in the absence of unique angiographically detectable stenoses requiring revascularization. There are strong evidences supporting that the FFR provides crucial functional information that could be related with morphological endovascular ultrasound findings, with the possibility to achieve same information in a cheaper, easier and more available manner. This review will focus on the current available literature regarding coronary flow reserve quantification and its clinical validation, suggesting and highlighting its current and future clinical applications.