Impact of prior myocardial infarction (MI) on infarct size and outcome in ST-segment elevation myocardial infarction (STEMI) patients

Background: Patients with a history of myocardial Infarction (MI) are at higher risk for recurrent cardiovascular events, including reinfarction and sudden cardiac death. Some of these effects of repeated MI may be explained by pre-condition through the previous insult. Data on long-term mortality and infarct size in patients presenting with ST-segment elevation myocardial infarction (STEMI) who report previous MI is scarce.

Objective: To evaluate the impact of prior MI on long-term mortality and infarct size in patients presenting with STEMI.

Methods and Results: This retrospective study included data of 1206 STEMI patients treated with primary percutaneous coronary intervention (PPCI). Patients were split into a group with reported previous MI (previous MI group, n=151 patients) and a group without a history of MI (no-MI group, n=1055 patients). In this cohort serial single-photon emission computerized tomography imaging was available with a first imaging session on admission and second 7 to 14 days thereafter. While there was no difference for the area at risk (AAR) before PPCI between the groups (median AAR (% of the left ventricle): 27.0% (IQR 15.0 – 44.0%) in previous MI vs. 22.0% (IQR 12.0 – 40.0%) in no-MI, p=0.63), patients with previous MI had a greater final infarct size (FIS) 7 to 14 days after MI (median FIS (% of the left ventricle): 16.7% (IQR 6.0–28.0%) in previous MI vs. 9.0% (IQR 2.0–22.0%) in no-MI, p<0.0001). Myocardial salvage index (MSI) was reduced in patients with prior MI (median MSI: 0.35 (IQR 0.11–0.63) in previous MI vs. 0.53 (IQR 0.27–0.82) in no-MI, p<0.0001). As a consequence, left ventricular ejection fraction was lower in patients with previous MI. At one year, 10 out of 151 patients in the previous MI group and 33 out of 1055 patients in no-MI group had died (Kaplan–Meier estimates of 1-year mortality: 7.1% vs. 3.4% (log-rank test: previous MI vs. no-MI, p=0.045). At 5 years, 25 out of 151 patients in previous MI and 76 out of 1055 patients in no-MI had died (Kaplan–Meier estimates of 1-year mortality: 19.8% vs. 7.2.% (log-rank test: previous MI vs. no-MI, p=0.0002).

Conclusion: Patients presenting with STEMI and a history of prior MI had a greater infarct size, reduced myocardial salvage, and a higher risk of one- and five-year mortality. These data indicate that a previous insult alters the response to a second insult.