A medical device including an ablation element. A thermally insulative sheath is included disposed within the ablation element. A fluid injection tube is disposed within a portion of the thermally insulative sheath. The ablation element passively transitions from a substantially linear geometric configuration to a substantially circular geometric configuration as the sheath is retracted proximally from a first position in which the sheath substantially encloses the fluid injection tube to a second position in which a portion of the fluid injection tube extends a distance away from the sheath.
