An interventional medical device system operable while within a body vessel is provided with a generally hollow tubular proximal portion, distal portion, and intermediate portion. The proximal portion and at least part of the distal portion remains outside of the body in use, with the remainder of the distal portion positioned within the body. The intermediate portion includes a spiral ribbon having adjacent turns, with at least one frangible bridge member between two adjacent turns. The proximal and distal portions are movable away from each other by elongating the spiral ribbon and, eventually, breaking the frangible bridge member. According to a method of using such a system to deploy an implantable medical device, such as an embolic coil, an actuation member is moved proximally with the proximal portion to disengage a bond or joint between the actuation member and the implantable medical device.