The diagnostic impact of prehospital 12-lead electrocardiography. STUDY HYPOTHESIS: It is feasible to apply prehospital 12-lead electrocardiography to most stable prehospital chest pain patients. Prehospital diagnostic accuracy is improved compared with single-lead telemetry. POPULATION: One-hundred sixty-six stable adult patients who sought paramedic evaluation for a chief complaint of nontraumatic chest pain. METHODS: One-hundred fifty-one prehospital 12-lead ECGs of diagnostic quality were obtained by paramedics on 166 adult patients presenting with nontraumatic chest pain. Paramedics and base station physicians were blinded to the information on acquired prehospital 12-lead ECGs and treated patients according to current standard of care-clinical diagnosis and single-lead telemetry. Final hospital diagnoses were classified into three groups: acute myocardial infarction (24); suspected angina or ischemia (61); and nonischemic chest pain (66). Paramedics and base station physicians' clinical diagnoses and prehospital and emergency department ECGs were similarly classified and compared. Prehospital and ED 12-lead ECGs were read retrospectively by two cardiologists. RESULTS: Paramedics achieved a high success rate (98.7%) in obtaining diagnostic quality prehospital 12-lead ECGs in 94.6% of eligible prehospital patients. For patients with acute myocardial infarction, prehospital ECG alone had significantly higher specificity than did the paramedic clinical diagnosis (99.2% vs 70.9%; P less than .001), and significantly higher positive predictive value (92.9% vs 32.7%; P less than .001). For patients with angina, combining the paramedic clinical diagnosis and the prehospital ECG significantly improved sensitivity (90.2% vs 62.3%; P less than .001) and increased negative predictive value (88.9% vs 71.3%; P less than .02) compared with paramedic clinical diagnosis alone. There was a high concordance between prehospital and ED ECG diagnosis (99.3% for acute myocardial infarction and 92.8% for angina). Furthermore, ten patients whose prehospital ECGs demonstrated ischemia and who had final hospital diagnoses of angina or acute myocardial infarction were mistriaged by paramedics and/or received no base station physician-directed therapy. CONCLUSION: It is feasible to apply prehospital 12-lead electrocardiography to most stable prehospital chest pain patients. Prehospital 12-lead ECGs have the potential to significantly increase the diagnostic accuracy in chest pain patients, approach congruity with ED 12-lead ECG diagnoses, and may allow for consideration of altering and improving prehospital and hospital-based management in this patient population. 