Final Diagnoses and Outcomes After Paramedic-Suspected ST-Segment Elevation Myocardial Infarction

Study objective Emergency medical services activate ST-segment elevation myocardial infarction (STEMI) pathways before biomarkers, imaging, or angiography are available. We sought to describe final hospital diagnoses, inhospital care, and outcomes among patients attended by paramedics for suspected STEMI in a statewide ambulance registry. Methods We conducted a retrospective statewide registry cohort study using the Victorian Ambulance STEMI Quality Initiative, with hospital follow-up data from January 2020 to June 2025. Principal International Classification of Diseases, 10th Revision, Australian Modification (ICD-10-AM) discharge diagnoses were grouped as STEMI; non-ST-elevation acute coronary syndrome or other coronary syndromes; other cardiac diagnoses; noncardiac diagnoses; and symptom-based diagnoses. Outcomes included out-of-hospital management, coronary angiography, percutaneous coronary intervention, complications, hospital length of stay, inhospital death, 30-day death, and mortality during follow-up. Associations were estimated with multivariable logistic and Cox regression and are reported as odds ratios or hazard ratios with 95% confidence intervals. Results Among 8,077 suspected STEMI visits with hospital follow-up data, 7,205 (89.2%) had a recorded discharge diagnosis and formed the primary analytic cohort; 872 (10.8%) had no recorded discharge diagnosis. Among the 7,205 with a recorded diagnosis, STEMI was confirmed in 4,330 (60.1%); 824 (11.4%) had non-ST-elevation acute coronary syndrome or other coronary syndromes, 760 (10.5%) other cardiac diagnoses, 613 (8.5%) noncardiac diagnoses, and 678 (9.4%) symptom-based diagnoses. Coronary angiography occurred in 4,836 (67.1%) and percutaneous coronary intervention in 3,200 (44.4%). Inhospital mortality was 8.6%, 30-day mortality 6.5%, and mortality during follow-up 17.5% (median follow-up 2.8 years). Compared with confirmed STEMI, adjusted mortality during follow-up was higher for noncardiac diagnoses (hazard ratio [HR] 1.75, 95% confidence interval [CR], 1.47 to 2.09); other cardiac (HR 1.14, 95% CI, 0.93 to 1.39), NSTE-ACS or other coronary (HR 1.16, 95% CI, 0.98 to 1.38), and symptom-based diagnoses (HR 1.09, 95% CI, 0.89 to 1.34) did not differ materially from STEMI after adjustment. Conclusion Within this statewide pathway population, paramedic-suspected STEMI identified a diagnostically heterogeneous, high-acuity group, in which approximately 60% of patients with a recorded discharge diagnosis had confirmed STEMI. These findings describe the suspected STEMI pathway population and should not be generalized to all confirmed STEMI or to all chest pain presentations. Emergency medical services and emergency department STEMI systems should preserve rapid access to reperfusion while supporting early diagnostic refinement and risk stratification for serious alternative diagnoses.