A rotatable operating head for removal of obstructive material from a target site in a body lumen or cavity is operably connected to a rotatable, translatable drive shaft, that is driven by a drive motor and received through an elongated catheter. The operating head includes a plurality of differential cutting blades, with at least one of the cutting blades being a stepped blade, the stepped blade comprising a raised cutting surface positioned adjacent, or in proximity to, a shoulder region.
