A medical manipulation assembly comprises a catheter including distal and proximal steerable portions with working channels. The assembly further comprises a steerable sheath through which the steerable portions extend. A distal steering mechanism, including a first lumen extending along a longitudinal axis of the catheter, bends the distal steerable portion. A proximal steering mechanism, including a second lumen extending along the axis and defined by a wall, bends the proximal steerable portion by rotational movement of the proximal steering mechanism independently of the distal steerable portion. The wall is rotatable about the axis. Distal pullwires extend between the distal steerable portion and the distal steering mechanism. Proximal pullwires extend between the proximal steerable portion and the proximal steering mechanism. The second lumen is axially aligned with an access lumen extending proximally from the proximal steering mechanism through which the distal and proximal working channels may receive a visualization instrument.