A novel index of infarct morphology predicts the presence of microvascular obstruction in patients with acute myocardial infarction

Background Microvascular obstruction (MO) has been associated with poor LV remodeling and adverse prognosis. Infarct morphology is related to the presence of MO in that patients with MO generally have larger infarct size (IS) and greater mean infarct transmurality. However, neither index is highly predictive on an individual patient basis. In the current study, we investigated the utility of a novel index of infarct morphology, which reflects the circumferential extent of fully transmural infarction extending to the epicardial surfacethe epicar- dial surface area (EpiSA) of infarctionto predict MO. Methods We studied 302 consecutive patients from 2 centers (Duke and Maastricht University) with first AMI. On contrast-enhanced-CMR, early (2-min post-contrast) and late MO (10-min post-contrast) were defined as hypoenhanced regions within hyperenhanced infarction. Infarct size, mean transmurality, and EpiSA were quanti- fied by manual planimetry of the stack of short-axis views. Results Patients were 58±11 years old (71% male). Prevalence of early and late MO was 64% and 55%, respectively. For the population, IS, mean transmurality, and EpiSA were 14% of LV mass (IQR 7-25%), 74% of infarct sector (IQR 57-86%) and 6% of total LV epicardial-surface-area (IQR 1-13%), respectively. All 3 infarct characteristics were significantly larger in patients with MO (all p 42% of LV (4% of population). However, only a small portion of the population (5%+4%=9%) had infarct size reaching these thresholds, showing that IS had limited discrimi- natory value on an individual patient basis. Similarly, infarct transmurality had limited discriminatory value. In contrast, EpiSA thresholds allowed ruling-in or rul- ing-out MO in a significantly larger percentage of the population (44% for both early and late; p<0.0001 com- pared with IS and transmurality). No patient had MO unless EpiSA was greater than zero. Multivariable analy- sis incorporating clinical, ECG, and CMR data demon- strated that EpiSA was the strongest, independent predictor of early and late MO (p<0.0001 for both). Conclusions The epicardial surface area of infarction, a novel index of infarct morphology, is a stronger predictor of MO than infarct size or mean transmurality. MO does not occur unless infarction extends to the epicardial surface.