INTRODUCTION AND EPIDEMIOLOGY
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.
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 About 1 in 500 children (age <18 years) are tested for VTE in EDs, with about 10% being diagnosed with VTE; the rate of diagnosis in children is rising, perhaps as a result of longer survival of children with chronic complex comorbidity and increased use of estrogen-containing oral contraceptives.2-4 VTE incidence varies slightly with geography across the United States but varies widely among hospitals.5 EDs with older, sicker patients diagnose more VTE cases. 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.6 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%.7
Morbidity from PE includes the post-PE syndrome, which occurs in about 25% of patients after PE and is characterized by chronic fatigue, dyspnea, exercise intolerance, and low perception of health status.8 An extreme form of post-PE syndrome, occurring in about 3% of PE patients, is chronic thromboembolic pulmonary hypertension, which causes disabling dyspnea.9 Morbidity from DVT includes PE and the postthrombotic syndrome, with the latter manifested as chronic leg swelling and pain; it occurs in about 20% of all ED patients with proximal DVT.10 Both PE and DVT have a spectrum of severity, with minor forms of the disease including distal PE (called subsegmental) and distal DVT (usually in the calf or saphenous veins).11
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 unprovoked (also called idiopathic).12 Provoked VTEs are a consequence of a triggering risk factor for clots, such as recent surgery, trauma, or any condition associated with limb or body immobility; active cancer can be a persistent provoking factor for VTE. 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).