Ostial renal nerve ablation

An ablation assembly comprising:

• an elongated member having a distal end and a proximal end and a length measured therebetween;
• an expandable member disposed at the distal end of the elongated member;
• at least one thermal element disposed on the expandable member;
• at least one electrically conductive wire connected to the at least one thermal element and extending substantially the length of the elongated member;
• and
• a ground electrode;
• wherein the at least one thermal element is configured to direct ablation energy along a localized electrical pathway between the at least one thermal element and the ground electrode to ablate nerve tissue between a first vessel in which the expandable member is located, and a second vessel adjacent the first vessel, without having to complete an electrical pathway to an exterior of the patient's body.

An ablation method using a catheter having an elongated shaft with a distal end and a proximal end, a ground electrode, and at least one thermal element connected to an expandable member positioned adjacent the distal end of the elongated shaft, the method comprising:

• positioning the distal end of the elongated shaft and the at least one thermal element in a first vessel;
• expanding the expandable member to position the at least one thermal element adjacent a wall of the first vessel;
• and
• conveying energy from the at least one thermal element to the ground electrode, thereby ablating tissue between the first vessel and a second vessel adjacent the first vessel.