A catheter apparatus for treatment of a human patient is described, the catheter apparatus having a central axis and comprising a shaping structure moveable between a delivery state having a first helical shape, and a deployed state having a second helical shape. The shaping structure is configured to have a reverse taper with a structural diameter that varies over the length of the shaping structure such that the structural diameter of the shaping structure at the proximal end is smaller than the structural diameter of the shaping structure at the distal end.