Current management of patients with acute coronary syndrome (ACS) and breathless-ness is based on a combination of clinical features, electrocardiogram (ECG), chest radiograph, and cardiac biomarkers. Initial categorization uses the ECG to divide patients into those with definitive changes such as ST-elevation, those with less specific changes such as ST-segment depression or T wave inversion, and those with no ECG abnormality. Patients with appropriate clinical features and ST-elevation ACS are categorized as ST-elevation myocardial infarction (STEMI). Management is based on immediate opening ofthe occluded artery by primary angioplasty or thrombolysis (7). Elevation ofbiomarkers such as cardiac troponin (8,9) at presentation or BNP (10-12) identifies a high-risk subset. To date, there are no clinically proven strategies that show these patients should be treated differently. Therefore, it is considered that immediate biomarker measurement will not alter patient management (7). Patients without STEMI will have a final diagnosis based on clinical features, ECG findings, and cardiac troponin measurement. In the general chest pain population, only a minority of patients present with STEMI, the majority having either low-risk unstable angina or nonischemic chest pain (Fig. 1) (13).
The clinical pathway of patients without STEMI is determined by biomarker measurement to define diagnosis and subsequent management strategy (14). There are three categories of patients that need to be identified. Patients with elevated troponin, nonspecific ECG changes, and appropriate clinical features have non-STEMI (NSTEMI). Exclusion ofNSTEMI is followed by further investigation to identify those patients with undetecta-ble troponin, nonspecific ECG changes, and appropriate clinical features who have unstable angina pectoris and those with a final diagnosis of nonischemic chest pain. The clinical environment in which diagnostic categorization occurs depends on the perceived risk of the patients. Patients considered at high risk of ischemic heart diseases are managed in a cardiac care environment whereas those at lower risk are managed in the emergency department (ED) or a chest pain evaluation unit. The difference is usually in the length of observation and intensity of the subsequent investigations.
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