We performed a randomized , double-blind , placebo-controlled trial in which , after perioperative interruption of warfarin therapy , patients were randomly assigned to receive bridging anticoagulation therapy with low-molecular-weight heparin ( 100 IU of dalteparin per kilogram of body weight ) or matching placebo administered subcutaneously twice daily , from 3 days before the procedure until 24 hours before the procedure and then for 5 to 10 days after the procedure .