Coronary microvascular dysfunction and flow reserve: an update

Non-invasive imaging techniques (positron emission tomography and cardiovascular/cardiac magnetic resonance) provide accurate and reproducible measurements of global and regional myocardial blood flow (MBF) in absolute units of ml/min/g of tissue, thus providing unique pathophysiological and diagnostic insights into the functioning of the coronary microcirculation. There is compelling evidence suggesting that, in many instances, in the absence of angiographically demonstrable stenosis of the epicardial coronary arteries, significant abnormalities of global myocardial perfusion can be demonstrated in individuals with either risk factors for coronary artery disease or different cardiomyopathies accompanied by alteration of the structure of the microvasculature. In this context, measurement of MBF gives unique diagnostic information regarding the functioning of the coronary microcirculation and provides a quantitative surrogate endpoint against which the efficacy of treatments can be established. In this review article, we discuss the more recent advances regarding the non-invasive measurement of MBF and flow reserve and their clinical applications for the detection of coronary microvascular dysfunction.