TnI identifies tissue damage in only a few
The diagnostic tool supports intensive evaluation
The troponin I (TnI) test to determine the likelihood of future cardiac events in chest pain patients is less helpful than previously thought.1 (See the April 1998 issue of Cost Management in Cardiac Care for a series of articles on TnI.)
The diagnostic and prognostic measure of levels of cardiac TnI released when heart tissue is damaged has been thought to accurately assess the amount of damage to the heart from a myocardial infarction (MI) or an episode of unstable angina. But now, a study has looked at the broader patient population who arrive at an emergency department (ED) complaining of chest pain, some of whom may not have an MI or unstable angina but may have other, less significant cardiovascular disorders, such as chronic heart failure or stable angina.
Boston researchers studied a group of chest pain patients who came to the ED at Brigham and Women's Hospital. TnI levels were elevated in most of the patients who later had an MI or another major cardiac event, but a significant proportion of the MI patients did not have an abnormal test. Furthermore, TnI elevations were found in some patients who did not later have a major cardiac event.
Investigators collected data on TnI and creatine kinase-MB fraction (CK-MB) during the first 48 hours from onset of symptoms in more than 1,000 patients. They confirmed TnI's role as a marker for myocardial ischemic syndromes, but concluded that the study does not support the routine use of TnI as a diagnostic tool in the ED. The test, according to study authors, performed significantly better than CK-MB mass assay, however, for predicting major cardiac events among patients ruled out for MI.
Carisi Polancyzk, MD, lead author on the study, speculated that any kind of damage to the heart, including that caused by chronic conditions such as heart failure or inflammation, may cause tissue to release TnI. Normal TnI levels do not necessarily guarantee a benign course, but patients with such values may be appropriate for exercise testing before discharge. Polancyzk said that the test might be more beneficial if it were used in patients with EKG abnormalities and other symptoms typical of MIs. The investigators' conclusion: The assay is an independent predictor of major cardiac events, but the positive predictive value is not high - only a minority of low-risk patients who develop major cardiac events will be identified by TnI.
Reference
1. Polanczyk CA, Lee TH, Cook F, et al. Cardiac troponin I as a predictor of major cardiac events in emergency department patients with acute chest pain. J Am Coll Cardiol 1998;32:8-14.
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