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Anticoagulation therapy is initiated in those at high risk of venous thromboembolism (VTE)

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Clinical Pearl 22-1

HIV+ pts have 40% increased risk to develop VTE vs an age-adjusted HIV cohort (Am J Emerg Med 2011;29:278); a variety of potential mechanisms have been proposed: protein S deficiency, antiphospholipid antibody (APA) syndrome, ↑ platelet activation/aggregation, & protease inhibitor use (Clin Appl Thromb Hemost 2004;10:277)

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  • High-risk pts generally fall into 1 or more of the following 3 categories: disruption in blood flow (atrial fibrillation, existing DVT/PE, immobilization, prolonged travel, heart failure); hypercoagulable state (genetic & acquired clotting abnormalities, cancer, pregnancy, drugs [thalidomide, estrogens], HIV, acute medical illness); or endothelial injury (prosthetic heart valves, recent surgery, endotoxins, hypoxia, indwelling catheters)
  • Common sites of thrombus formation
    • Deep leg veins (popliteal, saphenous, calf), left atrial appendage (common in atrial fibrillation), prosthetic heart valves; once formed, a deep venous thrombosis (DVT) may break loose & travel to the lungs, causing a pulmonary embolism (PE); a thrombus that forms in the left atrial appendage (or prosthetic valve) can embolize to the brain, resulting in a stroke

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Signs/Symptoms

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  • Deep venous thromboembolism (DVT) signs/symptoms are fairly nonspecific; swelling, redness, tenderness, or edema of affected limb; more specific signs are a palpable cord (typically popliteal vein), & Homan's sign (pain with dorsiflexion; 60–88% sensitive, 30–72% specific)
  • Pulmonary embolism (PE) symptoms include chest pain (CP), which may be pleuritic or substernal, dyspnea, tachycardia, & hemoptysis; often abrupt in onset, but can be gradual & persistent
    • May or may not have symptomatic DVT
  • Patient history required to identify risk factors & pretest probability of clot
  • Low-intermediate pretest probability of VTE should be augmented by quantitative methods prior to imaging: D-dimer (fibrin breakdown product) is nonspecific, but very sensitive; ↑ negative predictive value @ <500ng/mL; low pretest probability & negative D-dimer may be able to rule-out VTE
  • Those with high pretest probability may or may not benefit from D-dimer prior to imaging
    • Doppler ultrasound is typically 1st line for diagnosing DVT (inability to compress vein is diagnostic of clot); more sensitive imaging above the knee vs below the knee
    • Spiral CT or ventilation/perfusion scanning (V/Q) used to diagnose PE; patient-specific risk factors & facility protocol will dictate testing methods

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Table 22-1 Preclinical Assessment of DVT/PE Risk (Well's Criteria)

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