Objective: To determine the outcome of withholding anticoagulation from patients with suspected acute pulmonary embolism in whom computed tomographic (CT) findings are interpreted as negative for pulmonary embolism. Patients and Methods: This retrospective cohort study included 1512 consecutive patients referred from August 7, 1997, to November 30, 1998, for CT because of clinically suspected acute pulmonary embolism. All patients were examined by electron beam CT, and scanning was performed in a cephalocaudad direction from the top of the aortic arch to the base of the heart with 3-mm collimation, 2-mm table incrementation, and an exposure time of 0.2 second (130 peak kV, 620 mA, and standard reconstruction algorithm). Contrast material was infused at a rate of 3 to 4 mL/s through an antecubital vein with an automated injector. Findings on CT were interpreted as either positive or negative. The main outcome measures were deep venous thrombosis, pulmonary embolism, and vital status within 3 months after the CT scan and the cause of death based on medical record review, mailed patient questionnaires, and telephone interviews. Results: In 1010 patients (67%) CT scans were interpreted as negative for acute pulmonary embolism. Seventeen patients were excluded because they received anticoagulation. Of the remaining 993 patients, deep venous thrombosis or pulmonary embolism developed in 8; 118 patients died, 3 of pulmonary embolism. Nineteen patients were known to be alive, but additional clinical information could not be obtained. The 3-month cumulative incidence of overall deep venous thrombosis or pulmonary embolism was 0.5% (95% confidence interval, 0.1%-1.0%) and of fatal pulmonary embolism, 0.3% (95% confidence interval, 0.0%-0.7%). Conclusions: The incidence of (1) overall deep venous thrombosis or pulmonary embolism or (2) fatal pulmonary embolism among patients with suspected acute pulmonary embolism, negative CT results, and no other evidence of venous thromboembolism is low. Withholding anticoagulation in these patients appears to be safe.
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