Relationship and prognostic value of microvascular obstruction and infarct size in ST-elevation myocardial infarction as visualized by magnetic resonance imaging

Background Both infarct size and microvascular obstruction (MO) assessed by cardiac magnetic resonance imaging (CMR) are known to be predictors for adverse clinical outcome after ST-elevation myocardial infarction (STEMI).We hypothesized that a ratio of MO and infarct size (MO/infarct size) might be an even stronger predictor for outcome after STEMI, which has not been investigated yet. Methods STEMI patients reperfused by primary angioplasty (n = 438) within 12 h after symptom onset underwent contrast-enhanced CMR at a median of 3 days (interquartile range [IQR] 2;4) after the index event. MO and infarct size were measured 15 min after intravenous gadolinium injection. Follow-up was conducted after 19 months (IQR 10;27). The primary end point was defined as a composite of death, non-fatal myocardial reinfarction and congestive heart failure (major adverse cardiac events [MACE]). Results The extent of MO was only weakly correlated with infarct size (r = 0.21, p < 0.001). In a first multivariate analysis including extent of MO, infarct size, ejection fraction, end-systolic and end-diastolic volume, the extent of MO was independently associated with MACE (hazard ratio [HR] 1.03, 95%CI 1.02-1.05, p < 0.001). In a second multivariate analysis including MO/infarct size on top of the extent of MO, infarct size, ejection fraction, end-systolic and end-diastolic volume, MO/infarct size was identified as the strongest independent predictor for MACE (HR 2.22 [95%CI 1.60-3.08, p < 0.001]). Conclusions In contrast to infarct size, MO is associated with adverse clinical outcome after STEMI even after adjustment for other CMR parameters. However, MO/ infarct size is a more powerful predictor for long-term outcome after STEMI than either parameter alone.