How to study coronary microvascular dysfunction and its clinical relevance.

It is now accepted that the precipitation of acute coronary syndromes and, mostly, of acute myocardial infarction often occurs in patients who do not show critical stenoses. This and other findings challenge the relevance of stenosis severity as a major pathogenetic determinant in ischemic heart disease. Thus, a large amount of research has been put forward to investigate further mechanisms, besides changes in plaque burden and stenosis severity, associated with the precipitation of ischemia. Among putative mechanisms, great attention has been paid in the last decades to the activation of the atherosclerotic plaque and its complications, while only recently the interest has been focused on the potential role of coronary microcirculation as a cofactor in many clinical manifestations of ischemic heart disease. At present, the clinical evaluation of coronary microcirculation is hampered by a number of methodological limitations while the experimental models of coronary atherosclerosis and ischemic heart disease are still far from being satisfactory. As a consequence, although an involvement of the coronary microcirculation has been suspected in a large number of clinical syndromes, its nature and mechanisms still remain largely speculative. The present paper will try to critically review theoretical and technical approaches to the study of coronary microcirculation in ischemic heart disease with the aim at providing the reader with those elements potentially helpful to his own judgment on the matter.