Quantification of Absolute Coronary Blood Flow and Microvascular Resistance
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Fractional flow reserve (FFR) has transformed the way we look at a coronary angiogram and—more generally—the way we look at patients with stable coronary artery disease. Defining the presence of obstructive coronary artery disease and risk stratifying or treating patients can no longer be based merely on the 50% angiographic diameter stenosis1 but on a combination of angiography and FFR measurements.2 The latter has become the natural companion of the former, like echocardiography is a prolongation of the clinical examination. In addition, FFR can now be assessed noninvasively.3
See Article by Kanaji et al
Nevertheless, with angiography and FFR, the focus has remained on the epicardial arteries. This compartment of the coronary circulation is visible at angiography, is the site of potentially life-threatening lesions, is amenable to efficacious treatment (and immediately visible results), but it represents, after all, only 10% of the volume of the coronary circulation and has a mere conductive function.
In contrast, the microvasculature, with its amazingly complex structure, represents ≈90% of vascular volume.4 Its main functions are the …