Coronary microcirculation in acute myocardial ischaemia: From non-invasive to invasive absolute flow assessment.

Although substantial progress has been made in recent decades in reducing mortality and performing optimal revascularization in patients with myocardial infarction, ischaemic heart disease, including acute coronary syndrome, remains the leading cause of mortality worldwide. One of the remaining challenges is to better detect, prevent and treat extended myocardial damage despite angiographically optimal revascularization. Several indices are available in clinical practice to evaluate myocardial damage, infarct size and potential myocardial recovery. These indices are divided into two categories: non-invasive, generally performed after revascularization; and invasive, performed during the revascularization procedure. They allow the clinician to detect patients at risk and may help us to tailor the medical therapy and discharge strategy according to myocardial damage. Because of the number of indices, it is difficult to properly evaluate new therapeutics or to adopt one index that will provide sufficient data to better evaluate and understand the part of the coronary vasculature that is not seen - the microcirculation or so-called "black box". The aim of this review is to describe the non-invasive and invasive indices used to describe the microcirculation and their ability to predict clinical impact, and current dedicated therapeutics that may help to reduce microvascular damage and improve clinical outcomes.