Risk of pulmonary embolus with inferior vena cava thrombosis.

The authors have evaluated the risk of pulmonary embolism both as a primary event or as a secondary embolus despite adequate anticoagulation in 39 patients with phlebographically documented inferior vena caval (IVC) thrombosis. Twenty-six of these patients had thrombi characterized as free floating, and 13 had thrombi that were adherent to the IVC wall without a free-floating component. The incidence of initial pulmonary embolism confirmed by either pulmonary arteriography or high probability ventilation-perfusion lung scanning was 50 per cent (13/26) in those patients with free-floating IVC thrombi, but 15 per cent (2/13) in those with closely adherent mural thrombi (P less than 0.05). Pulmonary embolism despite adequate anticoagulation occurred in 27 per cent (7/26) of patients with free-floating clots, but in only 17 per cent (1/8) of cases with adherent thrombi (P greater than 0.05). These data strongly suggest that patients with documented free-floating inferior vena caval thrombi are at a significant risk for pulmonary embolism as an initial event and perhaps also as a recurrent embolus, even in the presence of adequate anticoagulation. When such thrombi are identified, the overall incidence of pulmonary embolus is high and conventional anticoagulant treatment with heparin may not be sufficient.