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INTRODUCTION AND EPIDEMIOLOGY
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Pulmonary embolism (PE) occurs when clotted blood enters the pulmonary arterial circulation. Most PEs result from deep vein thrombosis (DVT) in the legs, arms, or pelvis and occasionally from the jugular vein or inferior vena cava. The term venous thromboembolism (VTE) includes PE and DVT.
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In the United States, approximately 200,000 people will have new or recurrent PE diagnosed each year, and twice that many will have DVT without confirmed PE.1 VTE collectively affects about 1 in 500 persons per year in North America, and about 1 in every 300 adult ED patients receive the diagnosis (Figure 56-1). The incidence of VTE increases with age, peaking at 1 in 100 per year at age 80. Based on autopsy data, PE is the second leading cause of sudden, unexpected, nontraumatic death in outpatients.2 The case fatality rate from PE depends on the hemodynamic severity of the PE, age, and comorbid conditions; the case fatality rate is 45% for PE with circulatory shock, but only about 4% to 5% of patients with PE have shock. In patients with hemodynamically stable PE who are less than 50 years old and without other comorbidities, the case fatality rate is 1%.3
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Morbidity from DVT includes PE and the postthrombotic syndrome. The latter is manifested as chronic leg swelling and pain and occurs in about 20% of all ED patients with proximal DVT.4 Both DVT and PE present across a spectrum of severity, with recognition of minor forms of the disease, including distal PE (called subsegmental) and distal DVT, usually in the calf or saphenous veins.5
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Blood clots occur when coagulation exceeds the removal by fibrinolysis. Thrombophilias are conditions that tip the balance of coagulation-fibrinolysis toward excessive clotting. Most guidelines categorize VTE as provoked (or secondary) or unprovoked (idiopathic).6 Provoked VTEs are acquired and often time-limited conditions, generally often following recent surgery, trauma, or any condition associated with limb or body immobility; active cancer is a VTE provoker that often persists. Other provoking factors generally include diseases or conditions that impede venous blood flow, infection, chronic disease, estrogen use, pregnancy or initial postpartum interval, and age >50 years (each year after 50 increases the risk). Unprovoked VTE patients have no known risk factors, suggesting an increased tendency to clot.
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Most VTEs diagnosed in the ED are unprovoked.3,7...