Intracoronary drug administration may be desirable for a number of reasons and is used in therapeutic, diagnostic, interventional, and clinical research settings. One of the main indications for intracoronary drug administration is in the assessment of coronary blood flow either as a guide to intervention or as a clinical research tool. There are many methods of assessing coronary blood flow including the use of the angiogram derived corrected TIMI (thrombolysis in myocardial infarction) frame count1 and the rate of decorrelation of the radiofrequency signal from intravascular ultrasound (IVUS) imaging catheters.2 However, the most direct and widely used method of assessing coronary blood flow is the Doppler flow wire—a piezoelectric cell mounted on the tip of a 0.014 inch guide wire.3

The Doppler flow wire measures coronary blood flow velocity and, in order to measure coronary blood flow, knowledge of the cross sectional area of the vessel is required. The latter is usually estimated using quantitative coronary angiography (QCA), which assumes circular or elliptical luminal geometry, although greater accuracy can be obtained by using IVUS imaging catheters. Indices such as coronary flow reserve—the ratio of maximal to basal hyperaemic flow velocity—can be used to assess the functional severity of coronary stenoses and the dynamic integrity of the microcirculation without determining luminal cross sectional area. However, fractional flow reserve, which is measured using a pressure wire (guide wire with ability to measure distal coronary artery pressure), is increasingly being used to determine the functional severity of coronary stenoses since it is more reproducible, lesion specific, and less dependent on systemic haemodynamic parameters.4-6

Clinical research studies assessing coronary vasomotor responses to drug infusion have used endothelium dependent and independent vasodilators as well as agonists and antagonists of physiological mediators (table 1). The magnitude and variability of coronary responsiveness is highly …