Impact of the availability of a prior electrocardiogram on the triage of the patient with acute chest pain STUDY OBJECTIVE: To determine whether information from a prior electrocardiogram (ECG) improves diagnostic accuracy in the emergency department (ED) evaluation of patients with acute chest pain. DESIGN: Analysis of prospectively collected data from a cohort study. SETTING: Emergency departments of four community and three university hospitals. PATIENTS: 5,673 patients aged greater than or equal to 30 years who presented to the EDs of participating hospitals for evaluation of acute chest pain, including 772 (14%) with acute myocardial infarction (AMI). MEASUREMENTS AND MAIN RESULTS: After adjusting for clinical characteristics, no significant difference was found in the sensitivities of admission to the hospital or to the coronary care unit (CCU) between AMI patients with and without prior ECGs available for review. However, non-AMI patients with prior ECGs available for review were more likely to avoid CCU admission than were non-AMI patients without prior ECGs. This improvement in specificity was most marked in the 2,024 patients whose current ED ECGs had changes consistent with ischemia or infarction: when a prior ECG was available, non-AMI patients were more than twice as likely to be discharged (26% vs. 12%) and about 1.5 times as likely to avoid CCU admission (39% vs. 27%) (both p less than 0.0001). Admission rates of AMI patients with and without prior ECGs were similar. CONCLUSION: When the current ECG is consistent with ischemia or infarction, the availability of a prior ECG for comparison to determine whether the ECG changes are old or new improves diagnostic accuracy and triage decisions by reducing the admission of patients without AMI or acute ischemic heart disease (increased specificity) without reducing the admission of patients with these diagnoses (unchanged sensitivity). 