Table Pathophysiology of DVT Lower extremity DVT most often results from Impaired venous return (eg, in immobilized patients) Endothelial injury or dysfunction (eg, after leg fractures) Hypercoagulability Upper extremity DVT most often results from Endothelial injury due to central venous catheters, pacemakers, or injection drug use Upper extremity DVT occasionally occurs as part of superior vena cava (SVC) syndrome (compression or invasion of the superior vena cava by a tumor and causing symptoms such as facial swelling, dilated neck veins, and facial flushing) or results from a hypercoagulable state or subclavian vein compression at the thoracic outlet.