A catheter includes a body having a proximal region that extends along a longitudinal axis, a distal region predisposed into a loop via shaping wire, and a neck region between the proximal and distal regions. The loop is disposed in a plane generally orthogonal to the longitudinal axis. An activation wire is coupled to the distal region and to an actuator in a manner that allows a user to adjust the radius of the loop. The activation and shaping wires are contained within a tube-shaped constraint, such as a spring coil, within the neck in order to the neck from nodding when the activation wire is activated.
