Assessing Intermediate Coronary Lesions

Although invasive coronary angiography traditionally has been considered the reference standard for diagnosing coronary artery disease, its limitations are being highlighted with increasing frequency.1 This is particularly evident in patients with intermediate or moderate coronary artery lesions. For this subset of narrowings, a number of adjunctive, invasive techniques have been proposed to improve the diagnostic accuracy of the coronary angiogram.Article see p 2557In landmark work by Lance Gould and colleagues, coronary flow reserve (CFR) defined as hyperemic coronary flow divided by resting coronary flow, was first proposed as a method for evaluating the functional significance of intermediate stenoses.2 However, CFR by definition interrogates the status of the entire coronary circulation, both the epicardial vessel and the microcirculation. In patients with microvascular dysfunction, for example from diabetes mellitus or a past myocardial infarction, CFR will be abnormal, thus limiting its application for identifying ischemia-producing epicardial disease. CFR is also limited by its lack of a normal value in any given patient or vessel. For example, in 1 patient a value of 3 may be normal, whereas in another patient a value of 5 is normal. A final limitation of CFR is its variability or lack of reproducibility; because resting flow is a component of its definition, changes in resting flow that occur with hemodynamic perturbations can dramatically affect CFR.3,4 For these reasons, CFR has fallen out of favor for invasively evaluating intermediate coronary lesions.5Others have proposed intracoronary anatomic evaluation with techniques, such as intravascular ultrasound.6 Intravascular ultrasound provides improved morphologic assessment of intermediate coronary disease, but its ability to predict future events7 or to correlate with other measures of myocardial ischemia has been disappointing,8 because it fails to account for 1 of the most important determinants of the ischemic …