A cutting device for tissue separation includes a cutting edge using electrical energy such as RF power that is coupled to, but thermally insulated from, a catheter in an elongated medical device. Thermal insulation between a ring-type cutting device and the catheter is provided by a gap, slots within the ring, and/or slanted slots within the ring. In one embodiment, tissue separation occurs by rotation of a ring-type electrically-powered cutting edge having internal cross-bar elements. In an alternate embodiment, tissue separation occurs by longitudinal movement of an offset electrically-powered cutting edge that is pressed against tissue by an inflatable balloon. In a further alternate embodiment, a cutting edge is coupled longitudinally to a catheter, is provided electrical energy by wired connection to the braided catheter, but is thermally isolated from the catheter.