An intravascular device delivery system, the system comprising: an elongated member, the elongated member including: a steerable catheter (116, 216, 316) having a proximal end, a distal end, and a longitudinal axis extending therebetween; and a flexible hypotube (114, 214, 314) positioned radially outside and circumferentially about the steerable catheter (116, 216, 316) and coaxial with the steerable catheter (116, 216, 316), the flexible hypotube (114, 214, 314) including at least one island cut and at least one slit cut to direct flexibility of the flexible hypotube (114, 214, 314), wherein the flexible hypotube (114, 214, 314) and the steerable catheter (116, 216, 316) are rotationally fixed to one another at a first key assembly, a first tab (152, 252, 352) engaging with a first slot to form the first key assembly, and the first slot having a first slot length configured to at least partially determine an amount of longitudinal displacement of the steerable catheter (116, 216, 316) relative to the flexible hypotube (114, 214, 314) as the steerable catheter (116, 216, 316) extends distally beyond a distal end of the flexible hypotube (114, 214, 314) as the first tab (152, 252, 352) moves longitudinally within the first slot, characterised in that the steerable catheter (116, 216, 316) has a body (253, 353), the body (253, 353) including a lumen (255, 355) contained within a wall of the body (253, 353) that extends along a least a portion of a longitudinal length of the steerable catheter (116, 216, 316), and one or more cuts made in an outer surface of the body (253, 353) through to the lumen (255, 355), the first tab (152, 252, 352) being inserted into the one or more cuts, and the cuts being configured to retain the first tab (152, 252, 352) in the body (253, 353) of the steerable catheter (116, 216, 316) with at least a portion of the first tab (152, 252, 352) extending radially from the body (253, 353). an elongated member, the elongated member including: a steerable catheter (116, 216, 316) having a proximal end, a distal end, and a longitudinal axis extending therebetween; and a flexible hypotube (114, 214, 314) positioned radially outside and circumferentially about the steerable catheter (116, 216, 316) and coaxial with the steerable catheter (116, 216, 316), the flexible hypotube (114, 214, 314) including at least one island cut and at least one slit cut to direct flexibility of the flexible hypotube (114, 214, 314), a steerable catheter (116, 216, 316) having a proximal end, a distal end, and a longitudinal axis extending therebetween; and a flexible hypotube (114, 214, 314) positioned radially outside and circumferentially about the steerable catheter (116, 216, 316) and coaxial with the steerable catheter (116, 216, 316), the flexible hypotube (114, 214, 314) including at least one island cut and at least one slit cut to direct flexibility of the flexible hypotube (114, 214, 314), wherein the flexible hypotube (114, 214, 314) and the steerable catheter (116, 216, 316) are rotationally fixed to one another at a first key assembly, a first tab (152, 252, 352) engaging with a first slot to form the first key assembly, and the first slot having a first slot length configured to at least partially determine an amount of longitudinal displacement of the steerable catheter (116, 216, 316) relative to the flexible hypotube (114, 214, 314) as the steerable catheter (116, 216, 316) extends distally beyond a distal end of the flexible hypotube (114, 214, 314) as the first tab (152, 252, 352) moves longitudinally within the first slot, characterised in that the steerable catheter (116, 216, 316) has a body (253, 353), the body (253, 353) including a lumen (255, 355) contained within a wall of the body (253, 353) that extends along a least a portion of a longitudinal length of the steerable catheter (116, 216, 316), and one or more cuts made in an outer surface of the body (253, 353) through to the lumen (255, 355), the first tab (152, 252, 352) being inserted into the one or more cuts, and the cuts being configured to retain the first tab (152, 252, 352) in the body (253, 353) of the steerable catheter (116, 216, 316) with at least a portion of the first tab (152, 252, 352) extending radially from the body (253, 353).