A method and system for ablating a tissue region. In an exemplary embodiment, the method includes positioning a medical device including a deformable and helical distal portion in contact with a tissue region, the a helical distal portion including a plurality of turns each having a diameter, the diameter of each turn being greater than the diameter of the next distal turn, compressing the helical distal portion against the tissue region, deforming the distal portion into a substantially concentric spiral, and activating one or more treatment elements and ablating the target tissue. The method may further include advancing the uncompressed helical distal portion into a hollow anatomical feature, such as a pulmonary vein, and activating one or more treatment elements and ablating the target tissue.
