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Abstract
Each year in the United States about 6 million people present to the emergency department with acute chest pain, half of them are admitted for evaluation although only 15-20% of these people are finally diagnosed as acute coronary syndrome.
Previous studies have found that between 2 percent and 8 percent of patients with acute myocardial infarction who present to the emergency department are sent home. The rate of discharge of such patients represents about 11,000 missed diagnoses of myocardial infarction per year.
The term acute coronary syndrome (ACS) refers to any group of clinical symptoms compatible with acute myocardial ischemia and includes unstable angina (UA), non ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI).
Unstable angina and NSTEMI are closely related conditions: their pathophysiologic origins and clinical presentations are similar, but they differ in severity. A diagnosis of NSTEMI can be made when the ischemia is sufficiently severe to cause myocardial damage that results in the release of a biomarker of myocardial necrosis into the circulation. In contrast, the patient is considered to have experienced UA if no such biomarker can be detected in the bloodstream hours after the initial onset of ischemic chest pain.
Clinical symptoms of myocardial ischemia are very important in diagnosis, but there are non specific symptoms in one-third of cases, especially in diabetics and elderly patients. ECG changes have a low sensitivity which is only about 50%.
For these reasons the role of cardiac biomarkers in diagnosing acute coronary syndrome patients is very important. The activity of CK-MB isoenzyme has been used as a gold standard, but because of sensitivity limitation, other biochemical markers have been attempted such as myoglobin, cardiac troponin cTnT and cTn I. Combination of several biochemical tests will increase the diagnostic accuracy.
Approximately 40%-60% of patients with definite ACS present with an initial negative troponin result. Some are presenting early after onset of an acute MI before cardiac troponins are detectable in blood, the remainder are presenting with acute myocardial ischemia without necrosis (i.e., unstable angina). Discriminating these 2 groups from each other and from patients with non ischemic chest pain is a major clinical challenge. Thus, a biomarker that reliably detects myocardial ischemia in the absence of necrosis, will be a very important tool in diagnosis.