A delivery system assembly includes an elongate outer tube, an elongate inner member extending within a lumen of the outer tube, and an articulation sheath surrounding the outer tube between a handle of the assembly and a distal-most portion of the outer tube. The outer tube is longitudinally moveable within the sheath; and an inner diameter of the sheath is preferably smaller than that of the handle and the distal-most portion of the outer tube. Navigation of the assembly through a venous system, for deployment of an implantable medical device, is facilitated by deflection of the sheath, to orient a distal-most portion of the outer tube, within which an entirety of the medical device is contained/loaded, and by subsequent advancement of the distal-most portion, with respect to the sheath, to move the distal end of the inner member, along with the contained/loaded device into proximity with a target implant site.