Effect of Emergency Medical Service Use and Inter-hospital Transfer on Time to Percutaneous Coronary Intervention in Patients with ST Elevation Myocardial Infarction: A Multicenter Observational Study

BACKGROUND: The 2013 ACCF/AHA guideline for the management of ST elevation myocardial infarction (STEMI) recommends that patients be transported by emergency medical services (EMS) directly to a percutaneous coronary intervention (PCI)-capable hospital. We examined the effects of EMS use according to inter-hospital transfer on time to PCI in STEMI patients. METHODS: Adult patients diagnosed with STEMI from November 2007 to December 2012 with symptom onset less than 24 hours treated with primary PCI at 29 emergency departments (ED) were included. Patients with unknown information about important time variables, inter-hospital transfer and EMS use, and patients who already received PCI at another hospital were excluded. Patients were divided into groups according to EMS use and inter-hospital transfer: Group A (direct to final ED by EMS), Group B (transferred to final ED after EMS transport), Group C (direct to final ED not by EMS), and Group D (transferred to final ED after non-EMS transport). Symptom to balloon time less than 120 minutes was considered timely PCI. Multivariable logistic regression model adjusting for potential risk factors examined the relationship between the groups and timely PCI. Interactions between EMS use and inter-hospital transfer were also tested for the outcome. RESULTS: A total of 5826 patients were analyzed in this study, of which 28.3% called for EMS and 50% were transferred to another hospital for PCI. Median symptom to balloon time was 216 minutes. Timely PCI was achieved in 20.3% of the patients. With the Group D as the reference, the adjusted odds ratio (AOR) with 95% confidence intervals (95% CI) for timely PCI was 5.78 (4.81-6.95) for Group A, 0.80 (0.53-1.20) for Group B, and 2.87 (2.39-3.44) for Group C. In the interaction model, the AOR (95% CI) of EMS use in nontransferred groups and transferred groups was 2.01(1.71-2.38) and 0.80(0.53-1.20). CONCLUSIONS: EMS use significantly increased the odds of timely primary PCI to patients directly transported to a primary PCI center, but not in patients transferred from another hospital. EMS systems that identify STEMI patients and transport them to PCI capable hospitals, and processes to expedite the transfer of patients between non-PCI and PCI hospitals need to be developed further.