Prior myocardial infarction (MI) is a known risk factor for long-term mortality among acute MI patients; but its prevalence and implications for the short-term outcomes of patients with a new, acute MI remain uncertain.

We studied a total of 319,152 consecutively enrolled ST-segment elevation MI (STEMI) and non-STEMI (NSTEMI) patients in the National Cardiovascular Data Registry Acute Coronary Treatment and Intervention Outcomes Network Registry—Get With The Guidelines (01/2007-03/2012). Baseline characteristics, home and in-hospital treatments, mortality rates, and major bleeding were compared separately for STEMI and NSTEMI by prior MI status, with adjustment for mortality and major bleeding.

Prior MI was documented in 19% of STEMI (n = 124,535) and 29% of NSTEMI (n = 194,617) patients, who were older, were more likely to have comorbidities or prior revascularization, and were more commonly taking secondary prevention medications at home. Guideline-recommended treatments in-hospital and at discharge did not differ in prior-MI STEMI patients, but invasive management was lower for prior-MI NSTEMI patients. The frequency of in-hospital mortality was higher for prior-MI STEMI (5.9% vs 5.2%) and NSTEMI patients (4.3% vs 3.4%). After adjustment, the excess mortality risk associated with prior MI was no longer present for STEMI (odds ratio = 1.06, 95% CI 0.97-1.15), with only modest excess risk for NSTEMI (odds ratio = 1.10, 95% CI 1.04-1.15). The risk of in-hospital major bleeding was marginally lower for prior-MI NSTEMI.

More than 20% of patients with acute MI treated in contemporary practice have a history of a prior MI; despite differences in the baseline risk profile, there was little difference in the adjusted risk of in-hospital mortality by prior-MI status.