Study objective: To determine, during heparin therapy, the embolic risk associated with acute inferior vena cava thrombosis compared with noncaval thrombosis.
Design: Prospective controlled study.
Setting: University-affiliated general hospital.
Patients: Of 68 consecutive patients considered, 18 with cavographically proved inferior vena cava thrombosis and 45 with phlebography-proved noncaval proximal thrombosis met all other eligibility criteria and completed the study.
Interventions: All patients received adjusted continuous IV heparin therapy for ten days.
Measurements and results: All 63 patients underwent systematic baseline and "day 10" perfusion lung scanning and phlebocavography. None suffered pulmonary embolism within the ten days, but 11/63 patients showed thrombus extension on day 10 phlebocavograms. Retrospectively, no significant difference could be found between the groups with and without extension.
Conclusions: (a) The early embolic risk associated with heparin-treated venous thromboses appears low and does not seem to depend on the location (caval or more peripheral) of venous clots. (b) Thrombus extension may occur in spite of apparently "adequate" anticoagulation with heparin.