[Instantaneous wave-free ratio (iFR®) in patients with coronary artery disease]

[Coronary physiology in the catheter laboratory]

The regulation of coronary flow is mainly located in the resistance vessels of the microcirculation, so that the functional relevance of a coronary stenosis arises from the interaction between the epicardial stenosis and the downstream microcirculation. These complex interactions are precisely detectable by physiological measurements, such as the instantaneous wave-free ratio (iwFR) or the fractional flow reserve (FFR). In contrast, the purely visual assessment of the coronary anatomy could lead to misinterpretation and possibly to incorrect revascularization decisions. Consequently, in the current guidelines on myocardial revascularization of the European Society of Cardiology (ESC) the measurement of iwFR and FFR has a class IA indication in intermediate stenoses with unclear hemodynamic relevance. Despite this clear recommendation, physiological measurements are not yet regularly used in the clinical routine. Besides the purely hemodynamic assessment, novel methods such as co-registration and coronary mapping can be used for virtual planning of percutaneous coronary interventions, especially in vessels with diffuse lesions and serial stenoses. Furthermore, invasive flow measurements are also helpful for risk stratification between conservative and interventional treatment of patients with acute coronary syndrome, where additional factors of flow limitation, such as coronary spasm, thrombus and acute disturbance of the microcirculation play an important role.