Embolic coil delivery systems and components with frangible release features

A system for delivering an embolic coil device, comprising:

• a flexible elongate delivery shaft having a distal region and defining a delivery shaft lumen;
• an embolic coil device detachably connected to said distal region of said elongate delivery shaft, wherein said embolic coil device includes coil windings that define a coil lumen;
• an elongate pull wire positioned at least partially within said delivery shaft lumen and at least partially within said coil lumen, wherein said pull wire includes a frangible segment positioned within said coil lumen;
• and
• wherein said frangible segment of said pull wire defines a predictable region of separation of the pull wire in response to tensile force applied to the pull wire so as to detach said embolic coil device from said delivery shaft.