Predictors of Ambulance Transport in Patients with ST-Elevation Myocardial Infarction

Introduction: Despite intense public awareness campaigns, many patients with ST-elevation myocardial infarction (STEMI) do not utilize Emergency Medical Services (EMS) transportation to the Emergency Department (ED). Predictors for mode of transport by EMS versus private vehicle in patients with an acute STEMI were investigated. Hypothesis: It was hypothesized that patient characteristics, specifically older age, male sex, and a history of a prior cardiac intervention, would be associated with a higher likelihood of EMS utilization. Methods: A retrospective, observational cohort study was performed for all STEMI patients treated from April 1, 2007 through June 30, 2010 at an urban, academic ED with 24-hour cardiac catheterization available. Multivariable analyses with predetermined predictors (age, sex, prior cardiac intervention, weekend/evening arrival) were performed to investigate associations with mode of transport. Door-to-balloon (D2B) times were calculated. Results: Of the 209 STEMI patients, 11 were excluded, leaving 198 for analysis. Median age was 60 years (IQR: 53-70), 138 (70%) arrived by private vehicle, and 60 (30%) by EMS. The primary analysis did not identify significant predictors for EMS, but a posthoc model found that private insurance (OR 0.18; 95% CI, 0.07-0.45) was associated with fewer EMS transports. Although not statistically significant due to the great variability in time of arrival for STEMI patients transported by private vehicle, EMS transports had shorter D2B times. During business hours and weekend/evenings, EMS had D2B times of 50 (IQR: 42-61) and 58 minutes (IQR: 47-63), respectively, while private vehicle transports had median D2B times of 62 (IQR: 50-74) and 78 minutes (IQR: 66-106). Conclusion: No associations between mode of transport and patient age, sex, weekend/evening presentation and history of a prior cardiac intervention were identified. Privately insured patients were less likely to use EMS when experiencing a STEMI. More effective ways are needed to educate the public on the importance of EMS activation when one is concerned for acute coronary syndrome.