Early aspirin use is associated with decreased 30-day mortality in acute coronary syndromes

Abstract

Study objectives: Aspirin blocks the synthesis of thromboxane A 2 and platelet aggregation, making it a potent platelet inhibitor. In the setting of an acute myocardial infarction and unstable angina, these antithrombotic actions facilitate reperfusion of thrombosed coronary vessels. Experimentally, 100 mg of aspirin can inhibit platelet function within 60 minutes of ingestion. According to this, one would expect early aspirin use to decrease cardiac infarct size and, consequently, mortality in the setting of acute myocardial infarction. The goal of this study is to determine whether there is a difference in 30-day mortality between acute myocardial infarction and unstable angina patients ingesting aspirin within 1 hour of emergency department (ED) presentation and those given aspirin after 1 hour of presentation. Methods: This was a retrospective study of prospectively collected data from a registry of undifferentiated chest pain patients presenting to an urban tertiary care ED. The database is composed of a convenience sample of patients enrolled from September 1, 2001, to December 30, 2003, by trained research assistants from 8 am to 2 am 7 days a week. Patients were included in the database if they were older than 30 years, had an ECG performed, and presented with symptoms suggestive of acute coronary syndrome. Patients were included in this study if they had a final diagnosis of acute myocardial infarction or unstable angina. Patients were excluded if data on aspirin administration, aspirin time, or triage time were incomplete. Information collected included patient demographics, cardiac risk factors, medication use, treatments, diagnosis, and disposition. Myocardial infarction was defined in accordance with the World Health Organization criteria, including characteristic chest discomfort and serial elevation of cardiac markers. Unstable angina was defined as chest pain associated with a troponin level in the indeterminate range, a positive diagnostic test, or a stenosis greater than or equal to 70% in 1 or more epicardial coronary arteries on angiography. Follow-up was completed on all patients by telephone contact, medical record review, or death registry review. All reported deaths were included, regardless of cause. Univariate analysis was done to determine the association with cardiac risk factors, ED treatments, cardiac interventions, and final diagnosis with 30-day death. Significant variables ( P ≤.05) were then entered into a multivariate analysis using logistic regression. Results: The cohort of patients diagnosed with acute myocardial infarction or unstable angina included 527 patients, of whom 19 were excluded. Of these 527 patients, 75% ingested aspirin at home, in the ambulance, or in the ED. Forty-nine percent of patients were diagnosed with acute myocardial infarction, 51% with unstable angina. A total of 21 patients died. Aspirin use less than or equal to 1 hour of ED triage time ( P =.008, odds ratio [OR] 0.3, 95% confidence interval [CI] 0.1 to 0.7), percutaneous coronary intervention ( P =.01, OR 0.1, 95% CI 0.0 to 0.7), and a diagnosis of acute myocardial infarction ( P =.01, OR 3.2, 95% CI 1.3 to 8.0) were significant on univariate analysis. Only aspirin use less than or equal to 1 hour of ED triage time ( P =.04, OR 0.35, 95% CI 0.13 to 0.96) was significant on multivariate analysis. There was no difference in sex, age, ethnicity, cardiac risk factors, and ED administration of heparin, nitroglycerin, or β-blockers in patients who died at 30-day follow-up and those who survived. Conclusion: Aspirin use within 1 hour of ED presentation by patients with acute myocardial infarction or unstable angina is associated with a reduction in 30-day mortality compared with those given aspirin 1 hour after presentation. These results suggest that a protocol incorporating the triage administration of aspirin may improve 30-day survival in patients presenting with acute myocardial infarction or unstable angina.