A self-expanding medical device delivery system includes a plurality of trigger wires. The trigger wires retain a self-expanding medical device by forming a bend about structural members located on the proximal portion of the medical device. The proximal portions of the trigger wires have a greater diameter than the distal portions of the trigger wires to provide increased bending strength. An operator releases the self-expanding medical device by withdrawing the trigger wires in the distal direction. In some embodiments, a small portion at the proximal end of each trigger wire has a smaller diameter than the rest of the proximal portion. In other embodiments, the proximal and distal portions of each trigger wire each have a greater diameter than the center of the trigger wire.