Invasive Coronary Physiology for Assessing Intermediate Lesions

Atherosclerotic coronary artery narrowings, which provoke myocardial ischemia are the most common cause of angina pectoris and lead to adverse cardiac events.1 Removing the ischemic potential of a stenosis decreases symptoms and improves outcomes.2 Invasive coronary angiography remains the primary method for identifying coronary artery stenoses, but its inability to diagnose lesions responsible for inducing myocardial ischemia, particularly those of intermediate diameter stenosis remains a major limitation.3,4 To address this issue, there has been a long-standing interest in coronary wire-based methods for assessing coronary artery physiology. The goal of this review is to describe past efforts, define current standards, and address remaining controversy in the area of the invasive functional assessment of intermediate coronary artery stenosis.In the early 1970s, Gould et al5 performed seminal laboratory studies demonstrating that resting coronary flow remains unchanged with increasing epicardial coronary stenosis until the vessel lumen is >85% narrowed. They described the importance of inducing hyperemia to bring out the ischemic potential of more moderate coronary stenoses by measuring coronary flow reserve (CFR), defined as maximal coronary flow divided by resting flow. They showed that CFR had an inverse relationship to progressive coronary stenosis. However, it was not until the early 1990s, when a suitable Doppler wire became available to measure distal coronary flow velocity that invasive CFR and other velocity-based assessments could be performed readily in humans.6 Because coronary flow is proportional to coronary flow velocity, CFR can be estimated by measuring the coronary velocity at rest and during maximal vasodilation, typically after administration of adenosine.Subsequently, several studies were performed demonstrating the ability of Doppler wire-derived CFR to identify physiologically important coronary narrowings and to guide percutaneous coronary intervention (PCI).7,8 These experiences, however, highlighted some important limitations of this technique, which …