Low dose heparin in the prevention of deep-vein thromboses in patients with acute myocardial infarction.

Patients with acute myocardial infarction of less than 48 hours duration were randomized into three groups. The "fully anticoagulated" group received heparin by intravenous infusion and warfarin sodium to maintain a whole blood clotting time of 30 to 90 minutes and a prothrombin index of 10% to 35%. The "low dose" heparin group received 500 units by intravenous infusion every 12 hours. The control group received no anticoagulants. The radioactive fibrinogen test was used to diagnose the presence of leg vein thromboses. The control group had an incidence of venous thrombosis of 29.7% compared with 13.9% in the low dose group and 11.3% in the fully anticoagulated group. Patients in the control group who had cardiac failure had a significantly higher incidence of venous thromboses (71.4%) when compared with patients not in failure (20.0%). In the two treatment groups no significant difference was observed in patients with and without cardiac failure. Patients with cardiac failure complicating an acute myocardial infarction have a high incidence of venous thromboses. Anticoagulants significantly reduce this incidence and low dose intravenous heparin is as efficacious as full anticoagulation.