Patient Care Endocrinology & Cardiology - October 2007 - (Page 22)

I Troponins of cTn in the absence of pathology. The author has observed healthy patients who experienced extreme levels of anxiety and agoraphobia in response to receiving a misdiagnosis of acute coronary syndrome (ACS) that was based on an elevated cTn level. Although older assays were less sensitive and specific, with reports of false-positive results caused by circulating hemagglutinins, the assays currently in use do not have these drawbacks. Other problems do occur, however. The formation of macromolecular complexes is one example. As can be seen with various enzymes such as amylase, creatine phospho- Express Stop In patients with chest pain, the negative predictive value of the cardiac troponin level determined at 6 hours is quite good. kinase BB, and lactate dehydrogenase, autoantibodies can bind to the cTn and produce false elevations, in part due to slower degradation. Elevated rheumatoid factor levels can produce false elevations in cTn. If these antibodies bind to the same site as the monoclonal antibodies used in the assay, this phenomenon can produce false-negative test results as well. It is interesting that, in a rat model, autoantibodies were shown to trigger left ventricular (LV) dysfunction and heart failure. MI and ACS Measurement of cTn is now the standard for the diagnosis of MI. As with markers used in the past to make the diagnosis, the amount of cTn released into the circulation correlates with the size of the infarction. When reperfusion of the infarcted artery has occurred, whether by thrombolytic therapy or percutaneous transluminal coronary intervention, the time course of cTn release is altered. The peaks are higher, earlier, and narrower. As a result, the level of cTn measured in plasma after reperfusion may be greater than that expected for a similarsized infarction that had not been reperfused. Because the release of cTn may be prolonged due to the gradual release of the structural pool of the protein, cTn measurement may be less precise for the diagnosis of a myocardial reinfarction. Current American College of Cardiology/American Heart Association (ACC/AHA) guidelines suggest that this measurement not be utilized unless approximately 18 hours have passed since the original infarction.1 A few studies have suggested that earlier increases after a repeat infarction are meaningful, but only a small number of patients were included in these series. As a result of the way in which cTn is used to make a diagnosis of MI, a significant shift has occurred in the frequency and distribution of MI. Approximately 30% of patients previously diagnosed as having unstable angina based on negative CPK-MB assays are now classified as having non-STsegment elevation MI (NSTEMI). The classification of these patients as having an MI appears justified by the observation that a positive test for cTn confers a 4-fold increased risk of death or non-fatal MI compared to a cTn negative test. Multiple studies have demonstrated that cTn measurement is a highly accurate predictor of shortand long-term morbidity and mortality in ACS. As a result, the management of patients who present to the emergency department (ED) with chest pain is modified substantially by the results of this test. The negative predictive value of cTn determined at 6 hours is quite good. Because of the excellent positive predictive value, cTn measurement has been used to determine therapy in ACS. The test results identify a high-risk group, and these patients are much more likely to benefit from aggressive antithrombotic therapy with glycoprotein (GP) IIb/IIIa inhibitors or clopidogrel (Plavix), as well as an early invasive strategy. 22 PATIENT CARE ENDOCRINOLOGY & CARDIOLOGY www.patientcareonline.com http://www.patientcareonline.com

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Patient Care - Endocrinology & Cardiology - October 2007 Research Digest Contents Medicine in the News Recognizing and Managing Patients with the Metabolic Syndrome and Prediabetes Using Troponins to Evaluate Cardiac Injury The 15-Minute Visit Classified Advertising Clinical Clips

Patient Care Endocrinology & Cardiology - October 2007

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