Epidemiology, pathophysiology and natural history of venous thromboembolism.

Venous thromboembolism is a relevant social and health care problem for its high incidence, pulmonary embolism-related mortality, and long-term sequels which may be disabling. In the United States, there are at least 100,000 deaths per year from pulmonary embolism, found in over 10% non selected autopsy findings. The use of noninvasive diagnostic procedures has improved our knowledge on venous thromboembolism, with reference to surgery in particular. Deep vein thrombosis represents one of most common postoperative complications. Fatal pulmonary embolism is observed at least in one over thousand operated patients. From data of literature and in the authors' experience, the incidence of pulmonary embolism is decreasing in last years. Deep vein thrombosis is caused by several factors associated with Virchow's triad. Its evolution is site-related. While deep vein thrombosis of the calf can be considered a "benign" pathological condition for the incidence and severity of the embolic complication, as well as for the long-term outcomes, when the proximal venous trunks are involved, it is related to a high incidence of severe pulmonary embolism and relevant postphlebitic sequels. Pulmonary embolism is often the first manifestation of thromboembolism. Mobilization of thrombi is easier in the first phases, when they do not adhere as yet to the venous wall. Of 52 consecutive cases of pulmonary embolism, 21% occurred in the absence of signs or symptoms of deep vein thrombosis. In rare cases, thrombosis may be massive with total block of venous return flow and onset of ischemia. These forms have a severe prognosis apart from the embolic complication.