A detachment system for delivering an embolic coil implant to a treatment site is provided. A pull wire through a lumen of the detachment system that engages a loop wire can include a slack section. The slack section can be one or more bends, a spiral coil, or a stretchable material. The slack section is effective to inhibit premature detachment of the implantable medical device by inhibiting movement of the distal end of the pull wire when the detachment system is traversing a microcatheter.