[Relevance and methods for determining coronary flow reserve].

The assessment of coronary flow reserve, defined as the ratio of hyperemic to resting coronary blood flow, allows a more functional analysis of the coronary vasculature in addition to coronary angiography. Three different kinds of cardiac catherization procedures for measurement of coronary flow reserve will be reviewed with respect to reliability, feasibility and clinical significance in the diagnosis and treatment of diseases of coronary conductance and resistive vessels: first, from the techniques utilizing selective catherization of coronary sinus, the thermodilution and the oxymetry have to be considered qualitatively rather than quantitatively because of a large variance and an underestimation of hyperemic blood flow responses. The gas chromatographic argon method provides a more quantitative rationale for the selective measurement of resting and hyperemic coronary flow, and thus to more exact differentiation between a reduced hyperemic vs an increased resting flow as a major cause of a reduced flow reserve. Furthermore, because of a reliable reproducibility this approach allows to proceed follow up studies to assess impact of therapeutic interventions on coronary flow reserve in individual patients. Second, angiographic methods utilize either densitometry or time-to-arrival measurements of defined boluses of contrast medium. The utility of the TIMI-frame count and of densitometric algorithms will be discussed. These methods offer the advantage of being rather easy to handle and to be performed within routine coronary angiography. However, they can be applied to a only rather small group of patients because of methodological limitations in patients with multivessel disease, with disturbed left ventricular function and with irregular heart rate. Third, this group comprises methods in which devices have to be advanced into coronary circulation such as pressure or doppler guide wires, which allows selective assessment of regional coronary flow and reserve. Currently evaluated approaches to assess significance of coronary stenosis will be discussed. In conclusion, currently different methods for the assessment of coronary flow reserve are available in cardiac catherization laboratories and each of these methods provides specific advantages and disadvantages, which have to be considered to select the appropriate approach for the diagnosis of functional disturbances of the coronary conductance and resistance vessels. The obtained functional data on coronary circulation should always be interpreted only in context with myocardial function and clinical symptoms of the individual patient.