ABSTRACT
Introduction Intracoronary Doppler has several advantages for the assessment of coronary flow. Since there is a direct relationship between velocity and volumetric flow (where blood flow = vessel cross-sectional area X mean flow velocity) the differences or changes in Doppler coronary flow velocities can be used to represent changes in absolute coronary flow provided that the cross-sectional area remains constant. Doppler flowmeters directly measure the red blood cell velocity so that flow markers are not required, allowing a continuous assessment of flow velocity. Since the catheter can be selectively inserted in epicardial vessels, regional flow velocity measurements are possible. Intracoronary Doppler, however, also has several limitations. The most important limitation of intracoronary Doppler is the extreme dependency of the velocity measurements on the position of the Doppler probe within the vessel. If the sampling volume is small, or a large angle is present between ultrasound beam and long axis of the vessel, the measurement of flow velocity can be impossible or misleading, with an underesti mation of the peak coronary flow velocity. This limitation has been partially solved by recent techni cal developments, as will be discussed in this chapter. The different Doppler transducers available for intracoronary blood flow velocity measurements, the technique of assessment of coronary flow reserve and the methods for calculating absolute coronary flow from velocity and area measurements will be described.
