Role of coronary microvascular abnormalities in coronary artery disease-implications for perfusion imaging

The exact role and relative importance of the microvascular dysfunction in the pathophysiology and natural history of CAD is still to be defined. However, this disorder might affect imaging of both baseline and stress myocardial perfusion. A resting perfusion defect should not always be considered a marker of severe coronary stenosis not adequately counterbalanced by a maximal distal vasodilation. In fact, resting hypoperfusion does not necessarily imply exhaustion of vasodilator reserve and may be observed even in regions supplied by angiographically normal coronary arteries. Similarly, the absence of a perfusion defect during stress might indicate the presence of either a nonsignificant stenosis or a diffuse impairment in microcirculatory function. The possibility of obtaining absolute measurements of regional myocardial perfusion by positron emission tomography allows identification of mechanisms affecting myocardial blood flow regulation, providing a more precise characterization of CAD beyond simple agreement with the morphologic angiographic picture.