Coronary microvascular dysfunction

The link between myocardial ischemia and obstructive atherosclerosis is established beyond any doubt and coronary angiography has demonstrated a relationship between the severity and extent of coronary artery disease (CAD) and survival. In the past two decades, however, a number of clinical studies have highlighted the potential role of coronary microvascular dysfunction (CMD) in the pathogenesis of myocardial ischemia . There is evidence that CMD may precede the development of “classic” CAD in patients with cardiovascular risk factors. CMD can be so severe to cause angina even in the absence of detectable CAD and may contribute to generate ischemia in patients with overt CAD. Furthermore, CMD can contribute to myocardial ischemia in patients with cardiomyopathies and normal coronary angiograms and its severity is an independent predictor of clinical deterioration and death. Finally, CMD may be iatrogenic, i.e. it may follow percutaneous coronary interventions or coronary bypass surgery. In spite of the overwhelming evidence of the key pathogenetic role of CMD in different conditions, we still lack a systematic classification. The purpose of this article is to describe the structure and function of the coronary microcirculation, propose clinical and pathogenetic classifications of CMD and discuss the underlying mechanisms operating in each condition as well as the clinical implications.