An introducer assembly 10 for introducing an implantable medical device 16, e.g. stent, comprises a carrier 18 e.g. catheter, a sheath 24, a handle assembly 30,32, the handle assembly 30,32 being manually operable to retract the sheath 24, a drive assembly 50 coupled between the carrier 18 and sheath 24 which provides retraction assistance. The driver assembly includes a spring element 52 coupled to a yoke 56. The yoke 56 is coupled to a gripper element 58. The yoke 56 is coupled to a first handle unit 30 of the introducer 10. The sprung element 52 is coupled to a proximal handle unit 32. A brake element 66 acts to prevent operation of the sprung element 52 when no manual force is being applied to attract a sheath 24 and the assembly 10. When manual retraction force is applied to the assembly 50 the gripper element 58 the brake element 66 releases a sprung element 52 so that the lighter can apply a force assistance to assist in the retraction of the sheath 24 and thereby to assist in the deployment of a medical device.
