Central Illustration.

Limited Visualization of the Coronary Microvasculature With Invasive Coronary Angiography

(A) This figure illustrates a typical normal coronary angiogram (left) with a smooth and well-opacified left anterior descending coronary artery. The right image is a bismuth stereo angiogram from a cadaveric heart in work performed more than 50 years ago by the late Prof. S. Fulton (reproduced with permission from Fulton [30]). This image offers an unsurpassed illustration of the coronary microcirculation, contrasting starkly with the lack of microcirculatory information on the invasive coronary angiogram (30). (B) This schematic illustrates compartmentalized physiological assessment according to the probes acetylcholine and adenosine. The metrics fractional flow reserve and nonhyperemic pressure ratios are predominantly tests of epicardial coronary obstruction to blood flow, whereas index of microcirculatory resistance and hyperemic microcirculatory resistance are more specific to the microcirculatory function. Finally, coronary flow reserve is a metric that can be influenced by any combination of epicardial or microvascular disease or changes in resting flow.