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.