Clinical Impact of Persistent Microvascular Obstruction in CMR After Reperfused STEMI.

Background: Microvascular injury in the course of acute ST-segment-elevation myocardial infarction (STEMI) has been identified a as determinant of adverse outcomes and manifests as microvascular obstruction (MVO). MVO has long been regarded as a transient finding, vanishing within a few weeks after infarction. However, recent studies have shown that it may persist beyond the early phase, resulting in adverse remodeling. However, its clinical implications remain unclear. This study aims to evaluate the association of MVO persistence and major adverse cardiac events after STEMI.

Methods: In total, 609 patients with revascularized first-time STEMI underwent cardiac magnetic resonance imaging (CMR) at 4 days, 4 months, and 12 months after STEMI to assess MVO, infarct size, and left ventricular function. Major adverse cardiac events were defined as composite of death, reinfarction, and new congestive heart failure within a median interval of 3.2 years.

Results: Baseline MVO was present in 365 (60%) patients and persisted in 35 (10%) patients at 4-month CMR and in 20 (5%) patients at 12-month CMR. Compared with transient MVO not present at follow-up, patients with MVO persistence ≥4 months were more likely to experience major adverse cardiac events during follow-up (29% versus 13%; P=0.016). Within patients with MVO, those with MVO persistence had lower left ventricular ejection fraction (P=0.002), larger infarcts (P=0.00001), and more frequent intramyocardial hemorrhage (P=0.001) at baseline CMR.

Conclusions: Persistent MVO after STEMI occurs in up to 10% of patients with baseline MVO and is linked to major adverse cardiac events. Patients with MVO persistence had larger infarcts, lower left ventricular function, and more frequent intramyocardial hemorrhage at baseline CMR. All patients with MVO persisting ≥12 months initially showed intramyocardial hemorrhage.