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Figure 1 Acute Coronary Syndromes
The top half of the figure illustrates the chronology of the interface between the patient and the clinician through the progression of plaque formation, onset, and complications of UA/NSTEMI, along with relevant management considerations at each stage. The longitudinal section of an artery depicts the "timeline" of atherogenesis from (1) a normal artery to (2) lesion initiation and accumulation of extracellular lipid in the intima, to (3) the evolution to the fibrofatty stage, to (4) lesion progression with procoagulant expression and weakening of the fibrous cap. An acute coronary syndrome (ACS) develops when the vulnerable or high-risk plaque undergoes disruption of the fibrous cap (5); disruption of the plaque is the stimulus for thrombogenesis. Thrombus resorption may be followed by collagen accumulation and smooth muscle cell growth (6). After disruption of a vulnerable or high-risk plaque, patients experience ischemic discomfort that results from a reduction of flow through the affected epicardial coronary artery. The flow reduction may be caused by a completely occlusive thrombus (bottom half, right side) or subtotally occlusive thrombus (bottom half, left side). Patients with ischemic discomfort may present with or without ST-segment elevation on the ECG. Among patients with ST-segment elevation, most (thick white arrow in bottom panel) ultimately develop a Q-wave MI (QwMI), although a few (thin white arrow) develop a non–Q-wave MI (NQMI). Patients who present without ST-segment elevation are suffering from either unstable angina (UA) or a non–ST-segment elevation MI (NSTEMI) (thick red arrows), a distinction that is ultimately made on the basis of the presence or absence of a serum cardiac marker such as CK-MB or a cardiac troponin detected in the blood. Most patients presenting with NSTEMI ultimately develop a NQMI on the ECG; a few may develop a QwMI. The spectrum of clinical presentations ranging from UA through NSTEMI and STEMI is referred to as the acute coronary syndromes. This UA/NSTEMI guideline, as diagrammed in the upper panel, includes sections on initial management before UA/NSTEMI, at the onset of UA/NSTEMI, and during the hospital phase. Secondary prevention and plans for long-term management begin early during the hospital phase of treatment. *Positive serum cardiac marker. Modified with permission from Libby P. Current concepts of the pathogenesis of the acute coronary syndromes. Circulation 2001;104:365 (7); © 2001 Lippincott, Williams & Wilkins; The Lancet, 358, Hamm CW, Bertrand M, Braunwald E. Acute coronary syndrome without ST elevation: implementation of new guidelines, 1533–8. Copyright 2001, with permission from Elsevier (8); and Davies MJ. The pathophysiology of acute coronary syndromes. Heart 2000;83:361–6 (9). © 2000 Lippincott, Williams & Wilkins. CK-MB = MB fraction of creatine kinase; Dx = diagnosis; ECG = electrocardiogram.
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