A catheter for insertion into and treatment of tissue in a patient comprises a radio frequency (RF) electrode having an elongated body that conducts electrical RF energy to a conductive tip. An insulating sleeve surrounding the elongated body prevents leakage of RF energy from the elongated body when the catheter is being inserted into the tissue of the patient. In a first mode of operation, the conductive tip is exposed outside the insulating sleeve and the RF electrode delivers first RF energy capable of producing sparks that erode the tissue of the patient and create a tunnel through which the catheter can advance into the tissue of the patient. In a second mode of operation, the insulating sleeve is retracted to expose a portion of the RF electrode. Second RF energy is delivered to the volume of tissue around the catheter to necrotize the tissue by heating without producing sparks.