Materials and Methods
All protocols involved in this study were approved by an institutional review board.
Data were collected for 200 consecutive patients admitted to an urban ED with manifestations suggestive of acute myocardial ischemia, including those such as chest pain with or without radiation, chest pressure, shortness of breath, lower jaw pain, left arm pain, epigastric pain, syncope, hypotension, new or increasing lower extremity edema, palpitations, and other symptoms suggestive of an anginal equivalent. Cardiac biomarkers of necrosis (myoglobin, CK-MB, and TnI) were measured in the ED as part of the standard of care at the Massachusetts General Hospital, Boston.
Demographics, clinical information, and hospital course following enrollment were recorded for each patient via review of the medical records, performed by individuals blinded to all biomarker results. Data analyzed included records of the ED evaluation, all relevant electrocardiograms (ECGs), echocardiography, stress-testing data, cardiac catheterization data, admission history and physical examination findings, hospital course documentation, and discharge summaries.
Electrocardiographic criteria used to support a clinical diagnosis of myocardial ischemia were new findings of ST segment elevation of 1 mm or more in 2 contiguous leads, ST segment depression of 1 mm or more in 2 contiguous leads, new left bundle branch block, and T-wave inversions of 3 mm or more in 2 contiguous leads.
This information was organized and presented to a clinical cardiologist (J.L.J.) who was blinded to the results of the assay for IMA. Based on available data, a diagnosis of myocardial ischemia at the time of diagnosis was established or excluded for each patient. This decision was made in the light of objective and subjective data relevant to the nature of the patient's manifestations, including the results of history, physical examination, ECG, cardiac biomarkers (including those performed during the hospitalization) other than IMA, hospital course (including results of diagnostic studies such as cardiac catheterization), and discharge summaries. Ischemic syndromes included unstable angina, nonST segment elevation myocardial infarction (MI), and ST segment elevation MI. The definition of MI was as previously described.
Following initial evaluation, patients were divided into categories based on the presence or absence of myocardial ischemia, and their demographics, clinical characteristics, hospital course, and biomarker results were compared.
Serum samples and heparinized whole blood samples were obtained at the time of admission in standard collection tubes without anticoagulants. Initially, the whole blood samples were used to measure myoglobin, CK-MB, and TnI on a near-patient point-of-care testing platform (Triage, Biosite, La Jolla, CA). The lowest detectable limits for these tests are as follows: myoglobin, 2.7 ng/mL; CK-MB, 0.75 ng/mL; and TnI, 0.19 ng/mL. Measurement for IMA was performed with the Albumin Cobalt Binding Test (Ischemia Technologies, Denver, CO) on a Roche Hitachi 911 platform (Roche Diagnostics, Indianapolis, IN). The lowest detectable limit for this test is reported by the manufacturer to be 10 to 18 U/mL.
Data analysis was performed using SPSS statistical analysis software (SPSS, Chicago, IL). Univariate analyses between groups were done using χ2 cross-tabulations for categorical data and the Student t test for continuous data. All P values are 2-sided, with values less than .05 considered significant.
Following the identification of patients with and without myocardial ischemia, calculation of the sensitivity, specificity, and positive and negative predictive values for IMA and for parallel testing with the aggregate triple screen of myocardial necrosis biomarkers (myoglobin, CK-MB, and TnI) was performed.
Am J Clin Pathol. 2005;123(1):140-145. © 2005 American Society for Clinical Pathology
Cite this: Ischemia-Modified Albumin Improves the Usefulness of Standard Cardiac Biomarkers for the Diagnosis of Myocardial Ischemia in the Emergency Department Setting - Medscape - Jan 01, 2005.