An intravascular electrode system includes an expandable anchor and a flexible substrate which carries at least one electrode. The anchor is positioned in a blood vessel and expanded to an expanded position to bias the electrode in contact with the vessel wall. The flexible substrate may be longitudinally withdrawn from its position between the anchor and the vessel wall without removing the anchor from the blood vessel. A second flexible substrate may be longitudinally inserted into position between the anchor and vessel wall as replacement for the first substrate.