Coronary Artery Disease
A proposed strategy for utilization of creatine kinase-MB and troponin I in the evaluation of acute chest pain

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Abstract

In recent years, cardiac troponins have attracted great interest as a marker for myocardial injury. However, there are limited data on strategies for use of creatine kinase (CK)-MB and troponin I (cTnI) in clinical practice. We sought to develop a testing strategy using prospectively collected clinical data including serial CK-MB and cTnI levels from 1,051 patients aged ≥30 years admitted to a teaching hospital for acute chest pain. Diagnostic performance was evaluated for peak values of CK-MB and cTnI obtained during the first 24 hours for the combined end point of acute myocardial infarction and/or major cardiac events within 72 hours. The overall diagnostic accuracy was similar for both cardiac markers alone, and for the combination of cTnI and CK-MB (receiver-operating characteristic curve 0.84, 0.86, and 0.87, respectively). In the multivariate analysis, models including cardiac markers showed that both CK-MB and cTnI added information to clinical data to predict the combined end point, but cTnI added significantly less. Using recursive partitioning analysis, we developed a strategy that would restrict routine cTnI use to patients with normal CK-MB results and findings on the electrocardiogram consistent with ischemia. This strategy would divide patients with suspected myocardial ischemia into 4 groups with risks for the combined end point of 4%, 13%, 26%, and 85%. Thus, cTnI adds information to CK-MB mass and clinical data for predicting major cardiac events, but this contribution is mainly in patients with evidence of myocardial ischemia on their electrocardiograms.

Section snippets

Patient population

Eligible patients included all 1,139 emergency department patients aged ≥30 years who were admitted to the Brigham and Women’s Hospital between July 27, 1994, and June 30, 1995, for a chief complaint of acute chest pain that could not be explained by local trauma or abnormalities on chest roentgenograms. Eighty-eight patients were excluded because of incomplete cTnI or CK-MB data during the first 24 hours; therefore, 1,051 patients (92 %) constituted the study population.

Data collection

Data from the history,

Results

Among the 1,051 patients, acute myocardial infarction was diagnosed in 14%, and 37% were diagnosed as having unstable angina (Table I). At least 1 major cardiac event occurred within 72 hours from presentation for 9% of patients. The combined outcome of acute myocardial infarction and/or major cardiac events within 72 hours occurred in 19% of patients.

When CK-MB and cTnI results over the first 24 hours were compared for their diagnostic performance for this end point, cTnI was about as

Discussion

Our data indicate that cTnI does not appear to be a superior marker that should replace CK-MB, and that both assays need not be performed for all patients. Instead, our analysis supports a strategy that restricts routine cTnI use to patients with negative CK-MB results and electrocardiographic findings consistent with myocardial ischemia.

The results of our study are consistent with and extend the findings from previous research on cTnI in patients with unstable ischemic syndromes.1, 2, 3, 4, 5,

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    This study was supported by a grant from the Baxter Corporation, Chicago, Illinois.

    1

    Dr. Carisi Polanczyk is sponsored by a scholarship from Postgraduate Federal Agency (CAPES), Brasilia DF, Brazil.

    2

    Dr. Paula A. Johnson is the recipient of a Minority Faculty Development Award from the Robert Wood Johnson Foundation. %Manuscript received September 24, 1998; revised manuscript received and accepted December 15, 1998.

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