A catheter apparatus comprises an elongated catheter body having a distal end, a proximal end, and at least one fluid lumen extending longitudinally therein； and a plurality of flexible electrode segments on a distal portion of the catheter body adjacent the distal end, each pair of neighboring flexible electrode segments being spaced from each other longitudinally by a corresponding electrically nonconductive segment. Each flexible electrode segment comprises a sidewall provided with one or more elongated stiffness reductions extending through the sidewall, the one or more elongated stiffness reductions providing flexibility in the sidewall for bending movement relative to a longitudinal axis of the catheter body. The electrically nonconductive segment is substantially smaller in length than each of the corresponding pair of neighboring flexible electrode segments.
