Natural history of venous thromboembolism.

Venous thromboembolism (VTE) originates in systemic venous thrombosis and has different etiological mechanisms and natural history from arterial thrombosis. VTE typically originates as deep venous thrombosis in a lower extremity, where it may give rise to acute symptoms “upstream” from the obstructed vein, result in pulmonary embolism, and/or cause chronic venous obstruction. Pulmonary embolism may result in acute respiratory symptoms, cardiovascular collapse and, uncommonly, may also cause chronic disease.