Clinical Outcomes Associated With Various Microvascular Injury Patterns Identified by CMR After STEMI

Background The prognostic significance of various microvascular injury (MVI) patterns after ST-segment elevation myocardial infarction (STEMI) is not well known. Objectives This study sought to investigate the prognostic implications of different MVI patterns in STEMI patients. Methods The authors analyzed 1,109 STEMI patients included in 3 prospective studies. Cardiac magnetic resonance (CMR) was performed 3 days (Q1-Q3: 2-5 days) after percutaneous coronary intervention (PCI) and included late gadolinium enhancement imaging for microvascular obstruction (MVO) and T2∗ mapping for intramyocardial hemorrhage (IMH). Patients were categorized into those without MVI (MVO−/IMH−), those with MVO but no IMH (MVO+/IMH−), and those with IMH (IMH+). Results MVI occurred in 633 (57%) patients, of whom 274 (25%) had an MVO+/IMH− pattern and 359 (32%) had an IMH+ pattern. Infarct size was larger and ejection fraction lower in IMH+ than in MVO+/IMH− and MVO−/IMH− (infarct size: 27% vs 19% vs 18% [P < 0.001]; ejection fraction: 45% vs 50% vs 54% [P < 0.001]). During a median follow-up of 12 months (Q1-Q3: 12-35 months), a clinical outcome event occurred more frequently in IMH+ than in MVO+/IMH− and MVO−/IMH− subgroups (19.5% vs 3.6% vs 4.4%; P < 0.001). IMH+ was the sole independent MVI parameter predicting major adverse cardiovascular events (HR: 3.88; 95% CI: 1.93-7.80; P < 0.001). Conclusions MVI is associated with future adverse outcomes only in patients with a hemorrhagic phenotype (IMH+). Patients with only MVO (MVO+/IMH−) had a prognosis similar to patients without MVI (MVO−/IMH−). This highlights the independent prognostic importance of IMH in assessing and managing risk after STEMI.