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Thrombotic pulmonary embolism is not an isolated disease of the chest but a complication of venous thrombosis. Deep venous thrombosis (DVT) and pulmonary embolism are therefore parts of the same process, venous thromboembolism. Evidence of leg DVT is found in about 70% of patients who have sustained a pulmonary embolism; in most of the remainder, it is assumed that the whole thrombus has already become detached and embolised. Conversely, pulmonary embolism occurs in up to 50% of patients with proximal DVT of the legs (involving the popliteal and/or more proximal veins), and is less likely when the thrombus is confined to the calf veins. Rarely, the source of emboli are the iliac veins, renal veins, right heart, or upper extremity veins; the clinical circumstances usually point to these unusual sites.
Risk factors, epidemiology, and risk stratification
As pulmonary embolism is preceded by DVT, the factors predisposing to the two conditions are the same and broadly fit Virchow's triad of venous stasis, injury to the vein wall and enhanced coagulability of the blood (table 1). The identification of risk factors not only aids clinical diagnosis of venous thromboembolism, but also guides decisions about prophylactic measures and repeat testing in borderline cases.
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Risk factors for venous thromboembolic disease
Primary “thrombophilic” abnormalities are usually discovered after the thromboembolic event. Therefore, the risk of venous thromboembolism is best assessed by recognising the presence of known “clinical” risk factors. However, investigations for thrombophilic disorders at follow up should be considered in those without another apparent explanation. In many patients, multiple risk factors are present, and the risks are cumulative.
The overall incidence and mortality of pulmonary embolism in the population is unknown because the clinical diagnosis is unreliable, many events are asymptomatic, variable methods of prophylaxis are applied, necropsy rates are low, and death certification is inaccurate. Nevertheless, DVT and pulmonary …