Coronary Microvascular Obstruction

During the past decades, advances in percutaneous coronary intervention and antithrombotic therapy have improved the prognosis of patients with ST-segment–elevation myocardial infarction (STEMI). However, in a substantial number of STEMI patients, myocardial perfusion remains impaired despite successful recanalization of the infarct-related epicardial coronary artery, and this scenario has been shown to increase the risk of future cardiovascular events. Therefore, coronary microcirculation has been identified as an important determinant of outcome after STEMI. The potential causes and mechanisms of coronary microvascular dysfunction include pre-existing transient or permanent alterations, individual susceptibility, ischemic injury, reperfusion injury, and distal embolization of thrombotic material. The no-reflow phenomenon after percutaneous coronary intervention is the angiographic correlate for microvascular dysfunction and relies on reduced antegrade blood flow (thrombolysis in myocardial infarction flow grade and thrombolysis in myocardial infarction frame count) and impaired penetration of dye into the myocardium (myocardial blush grade and thrombolysis in myocardial infarction myocardial perfusion grade). Cardiac magnetic resonance (CMR) imaging enables the direct visualization and quantification of microvascular obstruction (MVO), which reflects myocardial damage resulting from microvascular dysfunction.